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supersymmetry is a well - motivated way to extend the standard model  ( sm ) . most impressively , supersymmetry can stabilize the large disparity between the size of the electroweak scale and the planck scale  @xcite . in addition , the minimal supersymmetric extension of the sm  @xcite , the mssm , leads to an excellent unification of the @xmath1 , @xmath2 , and @xmath3 gauge couplings  @xcite near @xmath4  gev , a scale that is large enough that grand - unified theory  ( gut ) induced nucleon decay is not a fatal problem . the mssm also contains a new stable particle if @xmath5-parity is an exact symmetry . this new stable particle can potentially make up the dark matter . the main obstacles facing supersymmetric extensions of the sm come from the requirement that supersymmetry be ( softly ) broken . to preserve the natural supersymmetric hierarchy between @xmath6 and @xmath7 , every mssm operator that breaks supersymmetry should be accompanied by a dimensionful coupling of size less than about a tev . however , for a generic set of soft terms of this size , consistent with all the symmetries of the theory , the amount of flavor mixing and cp violation predicted by the model is much greater than has been observed . instead , the experimental constraints require that the soft terms be nearly flavor - diagonal in the super - ckm basis  @xcite , and that nearly all the independent cp violating phases be very small  @xcite , or finely - tuned to cancel  @xcite . from the low - energy perspective , it is not clear why this should be so . a number of approaches to the supersymmetric flavor and cp problems have been put forward , such as adding new flavor symmetries to the mssm  @xcite , or mediating supersymmetry breaking through gauge interactions  @xcite or the superconformal anomaly  @xcite . these models also face new difficulties . new flavor symmetries typically require additional matter fields and hence the complications that go with them . gauge mediation generates flavor - universal soft masses and trivially small @xmath8 terms , but does not fully solve the cp problem , and makes it difficult to generate both the @xmath9 and @xmath10 terms with the correct size . anomaly mediation in its most simple form suffers from tachyonic slepton soft masses  @xcite . a more radical approach to the flavor and cp problems is to push the scale of the soft supersymmetry breaking scalar couplings to be much larger than the electroweak scale  @xcite . if this is done while keeping the gauginos relatively light , it is possible to preserve gauge unification and a good dark matter candidate  @xcite . of course , supersymmetry would no longer directly solve the gauge hierarchy problem if the scalar superpartners are very heavy .    another way to address the supersymmetric flavor problem , and the one we consider in the present work , is to have the soft scalar masses and the @xmath8 terms vanish simultaneously at a scale @xmath0  @xcite . if this scale is much larger than the electroweak scale , and if the gaugino masses do not vanish at @xmath0 , non - zero values for the scalar soft terms will be generated by radiative effects as the theory is evolved to lower energies . since the scalar soft terms thus induced are family - universal , the resulting soft spectrum does not have a flavor problem . the supersymmetric cp problem is also improved but not solved by this approach . besides the ckm phases , the only remaining phases are those of the gaugino soft masses , and the @xmath9 and @xmath10 terms . if the gaugino soft mass phases are universal , there are three new phases of which two can be removed by making field redefinitions  @xcite . the remaining phase can be eliminated as well within particular models  @xcite . near - vanishing soft scalar terms can arise in a number of ways . the canonical examples are the no - scale models of gravity mediated supersymmetry breaking . in these models , the absence of scalar soft terms is related to the flatness of the hidden sector potential that allows the gravitino mass to be determined by loop - corrections due to light fields  @xcite . a more recent construction that leads to near - vanishing soft scalar operators is gaugino - mediated supersymmetry breaking  @xcite . here , the mssm chiral multiplets are separated from the source of supersymmetry breaking by an extra - dimensional bulk , while the gauge multiplets propagate in the bulk . locality in the extra dimension(s ) leads to gaugino masses that are much larger than the scalar soft terms . small scalar soft terms can also be obtained from strong conformal dynamics in either the visible or the hidden sectors . in these constructions , the conformal running suppresses the scalar soft terms exponentially relative to the gaugino soft masses  @xcite . the main difficulty with very small input scalar soft masses is that the lightest sm superpartner particle is usually a mostly right - handed slepton , which can be problematic for cosmology . this is nearly always the case if gaugino universality is assumed to hold above @xmath11 , and @xmath12 . on the other hand , if @xmath0 is an order of magnitude or more above @xmath11 ( with gaugino universality ) , the lightest superpartner becomes a mostly bino neutralino . a viable low - energy spectrum can be obtained in this way  @xcite . for @xmath13 , a neutralino lsp can be obtained by relaxing the requirement that all soft scalar terms vanish at @xmath0 . one such generalization that does not re - introduce a flavor problem is to allow the higgs soft masses @xmath14 and @xmath15 to be non - zero at @xmath0 . these soft masses contribute to the running of the slepton masses through a hypercharge fayet - iliopoulos @xmath16-term , and can push the slepton masses above that of the lightest neutralino  @xcite .    in the present work , we study the phenomenology of the mssm subject to vanishing scalar soft terms . we generalize our study by including non - vanishing higgs boson soft masses , as well as a higgs boson bilinear @xmath17 term . this does not reintroduce a flavor problem . inspired by grand - unified theories , we take our input scale to be @xmath11 , and demand universal gaugino masses at this scale . after imposing consistent electroweak symmetry breaking , the independent parameters of this theory , which we call higgs exempt no - scale ( hens ) supersymmetry , are m_1/2 ,  ,  m_h_u^2 ,  m_h_d^2 ,  sgn ( ) , where @xmath18 is the universal gaugino mass at @xmath11 , @xmath19 is the ratio of the higgs boson expectation values , @xmath14 and @xmath15 are the soft higgs masses at @xmath11 , and @xmath20 is the sign of the supersymmetric higgs bilinear @xmath9 term . the outline of this paper is as follows . in section  [ theo ] we motivate this scenario , and show how it can emerge in a number of different ways . section  [ mass ] discusses the low - energy mass spectrum of the model , the acceptable regions of parameter space , and the most important constraints on these regions . in section  [ dark ] we investigate the prospects for dark matter in the model , and discuss some of the potential signatures this might induce . section  [ coll ] contains an investigation of some of the potential collider signatures of the model at the tevatron and the lhc , as well as a discussion of the discovery prospects at these machines . finally , section  [ conc ] is reserved for our conclusions . while this work was in preparation , we became aware of refs . @xcite , which investigate the mass spectrum and dark matter prospects of gaugino mediation with unsuppressed higgs soft masses . there is some overlap between their work and the material in sections  [ mass ] and [ dark ] of this paper . however , unlike refs  @xcite , we allow negative higgs soft squared masses at the input scale  @xcite , and have a more extensive discussion of the phenomenological constraints . on the other hand , they consider specific details of gaugino mediated models , and discuss the possibility of gravitino dark matter in more detail than we do . our primary motivation for considering models with small scalar soft terms is data driven : they provide a simple and elegant reason for small flavor violations induced by supersymmetry . even so , it is comforting that this framework can arise from a number of theoretical constructions . in this section we describe some of these models , and discuss how they can be modified to allow for non - vanishing soft masses for the higgs fields .      vanishing scalar soft terms have traditionally been associated with no - scale models  @xcite . these models are attractive because the gravitino mass , and therefore the scale of supersymmetry breaking , is determined dynamically . the basic assumption underlying no - scale constructions is that the effective superspace khler density and superpotential have the form  @xcite & = & -3m_pl^2 + f(x ) + f^(x^ ) + g(,^),[g - noscale ] + & = & w(),where @xmath21 is a hidden sector field , @xmath22 represents a visible sector field , and @xmath23 is a holomorphic cubic function . with this form of the khler density and superpotential , the tree - level potential along the direction of the hidden sector field @xmath21 is flat , the gravitino mass , @xmath24 is undetermined , and no soft terms are generated for the visible sector scalars . supersymmetry breaking is communicated to the visible sector by non - trivial @xmath21-dependent gauge kinetic functions , which generate gaugino soft masses on the order of @xmath24 . the one - loop corrections from the gauginos lift the potential in the @xmath21 direction and fix the value of @xmath24 to lie close to the electroweak scale , which is determined dynamically by the large top yukawa coupling  @xcite . it is difficult to maintain @xmath25 in no - scale models if there are other larger scales in the theory because of the radiative corrections these contribute to the effective potential for @xmath24  @xcite . if such large scales exist , such as in a gut , the heavy sector must be completely sequestered from the supersymmetry breaking , since in the supersymmetric limit , they do not alter the effective potential . within a gut where the higgs superfields are components of complete multiplets that also contain heavy fields , it is therefore essential to prevent these gut multiplets from obtaining a supersymmetry breaking mass . having separated the higgs in this way , it is natural to sequester the other chiral multiplets as well . this is the origin of the vanishing scalar soft terms in no - scale models . gaugino masses can be induced by a non - minimal kinetic function for those and only those components of the gut vector multiplet that remain light . thus if the higgs multiplets are components of a larger gut multiplet , of which some components develop gut scale masses , it is not possible to generate soft masses for the higgs fields without destabilizing @xmath24 . on the other hand , soft higgs masses might be possible in more general unification scenarios in which the higgs fields do not belong to complete gut multiplets  @xcite . the form of the no - scale khler density and superpotential , eq . ( [ g - noscale ] ) , is an input to these models . such a form does arise to lowest order in several string- and m - theory constructions , but is typically corrected at higher orders  @xcite . more generally , a superspace khler density in which the visible and hidden sectors appear as disjoint terms , as in eq .  ( [ g - noscale ] ) , is said to be _ sequestered _ @xcite . a sequestered khler density and superpotential guarantees that no direct soft terms are generated . this is a necessary ingredient for anomaly mediation  @xcite . complete sequestering can be obtained geometrically by confining the visible and hidden sectors to branes separated by an extra - dimensional bulk  @xcite . a partial sequestration can also be realized if the mssm gauge multiplets are allowed to propagate in the bulk , as in gaugino mediated supersymmetry breaking  @xcite . if so , the gauginos will develop soft masses through their local couplings to the hidden sector , while the soft terms of the chiral multiplets will only be generated by loops passing across the bulk . the resulting supersymmetric spectrum at the compactification scale of the extra dimension is therefore close to the one we are interested in : non - zero gaugino masses , and much smaller soft scalar terms . by allowing the higgs multiplets to propagate in the bulk , non - zero higgs soft terms can be generated as well . this is perhaps the simplest way to realize the hens models we shall consider . sequestering can also be realized in four dimensions through strongly - coupled conformal dynamics in the hidden sector  @xcite . even without strong conformal running , the contributions to the gaugino masses and the trilinear @xmath8 are naturally suppressed relative to the gravitino mass if there are no singlets in the hidden sector . this is not true for the scalar soft masses , which are generated by terms like d^4^_i_j x^x _ i^*_j , [ softmass ] where @xmath26 is the messenger scale , @xmath21 is a hidden sector field , and @xmath27 is a visible field . operators of the form of eq . ( [ softmass ] ) can be suppressed relative to the gravitino mass by strong conformal dynamics in the hidden sector that couples at the renormalizable level to @xmath21  @xcite . if all such soft mass contributions are sufficiently suppressed , and if there are no hidden sector singlets , the visible sector is sequestered and the leading contribution to the soft terms comes from anomaly mediation . by allowing singlets in the hidden sector , both gaugino masses and @xmath8 terms can be generated that are much larger than the anomaly - mediated terms  @xcite . this is close to , but not quite , the spectrum we are interested in , because it is unclear how to avoid suppressing the higgs soft masses while squashing the rest .    a partial sequestration of soft terms , as well as an explanation for the yukawa hierarchy , can also be obtained from strong conformal dynamics in the visible sector  @xcite . in these constructions , there is a new gauge group @xmath28 that approaches a strongly - coupled fixed point in the ir . the mssm fields are not charged under @xmath28 , but they do couple to fields that are through cubic operators in the superpotential . as the theory flows towards the fixed point , the mssm fields develop large anomalous dimensions which suppress their corresponding ( physical ) yukawa couplings . since different ( linear combinations of ) fields develop distinct anomalous dimensions , related to their effective superconformal @xmath5 charges , a yukawa hierarchy can be generated in this way  @xcite . the conformal running also produces a general suppression of the soft scalar masses , as well as a hierarchy of trilinear @xmath8 terms that mirrors the yukawa couplings  @xcite . conversely , the gaugino masses are largely unaffected because they do not couple directly to the strongly - coupled sector . the third generation multiplets and the higgs multiplets must also be shielded from the conformal running effects to avoid suppressing the top quark yukawa coupling . as a result , the third generation and the higgs soft masses do not get suppressed . thus , the spectrum from visible sector conformal running is similar to one we shall consider , but augmented by third generation soft masses and @xmath8 terms . we expect the phenomenology of both scenarios to be similar over much of the allowed parameter space .      from the discussion above , we see that a hens soft mass spectrum can arise from gaugino mediation with the higgs multiplets in the bulk , or from conformal running in the hidden sector up to additional contributions to the third generation states . before proceeding , however , let us comment on our choice of @xmath11 as the input scale for the soft spectrum . in gaugino mediation , the input scale is on the order of the compactification scale , @xmath29 . , is less than the cutoff of the theory . ] for visible - sector conformal running , the input scale for the soft spectrum is the scale at which the conformal running ceases , which we will also call @xmath29 . our motivation to set @xmath30 is partly conventional , but is also motivated by gauge unification and our wish to strongly suppress the scalar soft masses .    in both cases , gauge unification can be preserved with @xmath31 , but the process will be more complicated than in the standard picture . in gaugino mediation , kaluza - klein states appear above @xmath29 and can lead to an accelerated power - law running  @xcite . with conformal dynamics in the visible sector , the sm gauge coupling beta functions will be modified by the large anomalous dimensions of the mssm fields . gauge unification will still occur , albeit at a lower scale , provided the conformal dynamics respects a global symmetry into which the sm gauge group can be embedded  @xcite . thus , in each case having @xmath29 below @xmath11 can induce an effective unification of the sm gauge couplings below the apparent unification scale @xmath32 . this is problematic for many gut completions of the mssm , which predict baryon and lepton number violation . typically , some additional structure is needed if @xmath29 is much smaller than @xmath11 . this motivates us to consider @xmath33 . it is clear that gauge unification can also be maintained with @xmath34 . if @xmath29 is larger than @xmath11 , the renormalization group running from @xmath29 down to @xmath11 will induce non - vanishing ( flavor - universal ) soft masses at @xmath11 . the size of these corrections from running above @xmath11 depends on the precise @xmath35 completion of the theory , but even for minimal @xmath35 models they can be significant , on the order of  @xcite a & & c_a ( ) m_1/2,[abovemg ] + m^2 & & c_m^2 ( ) m_1/2 ^ 2,where @xmath36 is the gut coupling , and @xmath37 and @xmath38 are dimensionless constants on the order of or slightly larger than unity . these contributions can be large enough for an acceptable low - energy spectrum to be obtained  @xcite . on the other hand , in both gaugino mediation and conformal sequestering , @xmath29 can not be more than about an order of magnitude above @xmath11 because the suppression of soft terms ( and yukawa couplings ) requires a separation of scales . let @xmath39 be the scale at which conformal running begins in the case of conformal dynamics , or the @xmath40 cutoff of the extra - dimensional gauge theory in gaugino mediation . presumably @xmath41 . the amount of suppression of the soft scalar terms from conformal running is expected to be an order - one power of @xmath42 , whereas the required suppression is typically on the order of @xmath43  @xcite . an even stronger upper bound on @xmath0 can be obtained if the conformal dynamics are responsible for the small electron yukawa coupling as in ref . the condition for this is y_e ( ) ( ) ^(_l+_e)/2 , where @xmath44 denote the anomalous dimensions of @xmath45 and @xmath46 , which are generally smaller than 2 . if we take this bound seriously , @xmath29 can be at most only slightly larger than @xmath11 . in gaugino mediation , flavor - mixing contact interactions between the mssm chiral multiplets and hidden sector operators , arising from bulk states with masses above the uv cutoff scale , are suppressed by a factor of @xmath47  @xcite . again this factor must be less than about @xmath43 to avoid various experimental flavor constraints , which translates into @xmath0 being within an order of magnitude larger than @xmath11 ( for @xmath48 ) .    given the above considerations , we will set @xmath30 throughout this paper , and not concern ourselves with the precise mechanism by which the scalar soft terms are suppressed . while beyond the scope of the present work , it also interesting to speculate that the breaking of the gut symmetry is related to the geometry of the extra dimension , or the escape from conformal running . such a construction would further justify our choice of @xmath30 . finally , let us also note that within particular models there is typically some residual flavor violation due to an incomplete suppression of the scalar terms at @xmath29 . the amount of flavor suppression can be close to the level probed by current experiments . however , without specifying a particular model , it is not possible to perform an analysis of the constraints due to flavor physics . thus , we assume as our starting point that at the scale @xmath49 , all scalar masses except those of the higgs bosons are precisely zero and that corrections to that assumption are inconsequential to the phenomenology discussed below . the essential features of the hens mass spectrum are well illustrated by a simple one - loop analysis . at this order , the ratio @xmath50 , @xmath51 , is scale invariant for all three gaugino masses . if the gauge couplings unify and the gaugino masses are universal at @xmath11 , it follows that at lower scales q , @xmath52 ^ 2 m_{1/2}$ ] . for @xmath53 , this gives    m_1 ( 0.43)m_1/2 ,  m_2 ( 0.83)m_1/2 ,  m_3 ( 2.6)m_1/2.[2:m12 ]    the one - loop running of the scalar soft masses is given by  @xcite ( 4)^2 x_i -8_ac^a_ig_a^2|m_a|^2 + g_1 ^ 2y_is , [ 2:msoftrun ] where @xmath54 depends on the soft masses and @xmath8 terms and is usually proportional to yukawa couplings , @xmath55 is the quadratic casimir for the representation @xmath56 under gauge group @xmath57 , and s = ( m_h_u^2-m_h_d^2 ) + tr_f(m_q^2 - 2m_u^2+m_e^2+m_d^2-m_l^2 ) , [ 2:sterm ] with the trace above running over flavors . at one - loop order , the rg equation for the @xmath58 term is particularly simple , ( 4)^2 = g_1 ^ 2s . because of this simple form , the effect of the @xmath58-term on the low - scale soft masses is to simply shift the value they would have with @xmath59 by the amount m_i^2 = -s_gut -(0.052)y_is_gut , where @xmath60 evaluated at @xmath11 .    neglecting yukawa effects , the low - scale slepton soft masses at @xmath61 are m_l^2 & & ^2 + ( 0.052)s_gut , [ 2:mslepton ] + m_e^2 & & ^2 - ( 0.052)s_gut . if mixing effects are small , the physical slepton masses will be close to @xmath62 and @xmath63 , up to the @xmath3 @xmath16-term contributions . the mass of the lightest neutralino is usually close to @xmath64 ( under the assumption of gaugino universality ) unless @xmath9 is relatively small .    comparing eq .   with eq . , we see that for @xmath65 , @xmath66 is less than @xmath64 and the lightest superpartner tends to be a mostly right - handed slepton . on the other hand , if @xmath67 , the right - handed slepton soft mass is pushed up relative to @xmath64 , allowing for a mostly bino neutralino lsp . for @xmath68 very large and negative , the lsp can be a mostly left - handed slepton . relative to the sleptons and the electroweak gauginos , the squarks and gluino are very heavy because the @xmath1 gauge coupling grows large in the infrared .      to confirm the simple analysis given above , we have performed a scan over the hens parameter space using suspect  2.34  @xcite . this code performs the renormalization group running at two - loop order with one - loop threshold effects , and includes radiative and mixing corrections to the physical particle masses . we take @xmath69  @xcite and @xmath70  gev  @xcite in our analysis . for each model parameter point we require consistent electroweak symmetry breaking , and superpartner masses above the lep  ii and tevatron bounds ( @xmath71  gev , @xmath72 , @xmath73 ) . we also impose the lower - energy constraints & & [ -8,24]10 ^ -4  @xcite + br(bs ) & & [ 3.0,4.0]10 ^ -4  @xcite + a _ & & [ -5,50]10 ^ -10  @xcitethese ranges correspond approximately to the @xmath74 allowed values , although we have allowed a slightly larger range for @xmath75 . the constraint from the muon magnetic moment is particularly interesting in hens scenarios , and we shall discuss it more extensively below . in the immediate analysis we do not include the lep  ii bound on the lightest higgs boson mass . we will discuss this constraint below as well .     and the differently colored regions in the figure indicate the identity of the lightest superpartner . the quantities @xmath14 and @xmath15 are evaluated at the input scale @xmath11.,scaledwidth=70.0% ]     and @xmath77 . the differently colored regions in the figure indicate the identity of the lightest superpartner . the quantities @xmath14 and @xmath15 are evaluated at the input scale @xmath11.,scaledwidth=70.0% ]     and @xmath77 . the differently colored regions in the figure indicate the identity of the lightest superpartner . the quantities @xmath14 and @xmath15 are evaluated at the input scale @xmath11.,scaledwidth=70.0% ]    figures  [ lsp-10 - 300 ] , [ lsp-10 - 500 ] , and [ lsp-30 - 500 ] show the allowed regions of @xmath78 and @xmath79 , for @xmath80 equal to @xmath81 , @xmath82 , and @xmath83 , subject to the constraints described above . the soft higgs masses in these plots are re - expressed in terms of the more convenient combinations @xmath84 , and @xmath85 , where @xmath86 denotes the signed square root ( @xmath87 ) . also shown in these plots is the identity of the lightest superpartner at each allowed parameter point . these figures confirm our previous approximate analysis . when @xmath68 is positive or zero , the lsp is a mostly right - handed stau or selectron . as @xmath68 becomes more negative , a neutralino becomes the lsp , while for very large and negative values of @xmath68 the lsp is a sneutrino . for extremely large positive or negative values of @xmath68 , one of the slepton soft masses becomes tachyonic . the allowed parameter region is cut off at larger positive values of @xmath88 because @xmath89 only has a negative solution , implying that electroweak symmetry breaking is not possible . reaches zero by the @xmath90 and the chargino mass constraints . ] note that in fig . [ lsp-10 - 500 ] , there is a thin strip along the upper border of the allowed region in which the lsp is a neutralino . in this strip , the @xmath9 term is smaller than @xmath64 and the neutralino lsp is mostly higgsino . for larger negative values of @xmath88 , @xmath91 and the parameter space gets cut off by the bound from @xmath90 . as @xmath88 becomes even smaller , electroweak symmetry breaking ceases to occur . the effects of the @xmath92 yukawa coupling and left - right mixing can be seen by comparing figs . [ lsp-10 - 500 ] and [ lsp-30 - 500 ] . in the models we are considering , the value of the yukawa - dependent term in eq .   for the right - handed stau soft mass is x_e_3 2|y_|^2m_h_d^2 . the left - right mixing is also proportional to the @xmath92 yukawa . as @xmath19 increases , so too does the @xmath92 yukawa , and therefore also the yukawa effect on the running and the mixing . left - right mixing tends to push the lighter stau mass lower , and for this reason it is more difficult to obtain a neutralino lsp at larger values of @xmath19 . however , there is also a competing effect from the influence of the @xmath92 yukawa on the running of @xmath93 . when @xmath15 is large and negative , the @xmath94 term increases the value of @xmath93 at low energies . thus , a selectron or an electron sneutrino is the lsp in some parts of the parameter space .    in parts of the parameter space shown in figs . [ lsp-10 - 300]-[lsp-30 - 500 ] the value of @xmath14 is large and negative , while the slepton soft masses are considerably smaller in magnitude ( but positive ) . in these regions , it is likely that the standard mssm minimum is only metastable , and that a deeper charge - breaking minimum exists at large field values  @xcite . the precise constraints on the existence of such non - standard global minima depend on the details of the thermal history of the universe  @xcite , and we do not investigate them in the present work . however , a necessary condition is that the lifetime of the metastable mssm vacuum at @xmath95 should be greater than the age of the universe . while beyond the scope of the present work , it is possible that some regions of the parameter space shown in figs .  [ lsp-10 - 300]-[lsp-30 - 500 ] , especially the lower left region and at larger values of @xmath19 , may not be populated after a more detailed analysis . since the sleptons in hens models are relatively light , the corrections to the anomalous magnetic moment of the muon , @xmath97 can be significant  @xcite . currently , the measured value of @xmath98 exceeds the sm prediction by about two standard deviations  @xcite , a _ = a_^exp - a_^sm = ( 2210)10 ^ -10 . this result is suggestive of new physics .    in the mssm , there are additional contributions to @xmath99 from loops involving a virtual chargino and muon sneutrino , and loops with a virtual neutralino and smuon . for the hens scenarios we are studying , in which all masses scale predominantly with @xmath18 and the gaugino masses are universal ( and assumed real and positive ) , the leading supersymmetry contribution to @xmath98 is proportional to @xmath19 , scales roughly as @xmath100 , and has a sign equal to the sign of the @xmath9 term , @xmath20  @xcite . given the tension between the measured value of @xmath75 and the sm prediction , @xmath101 is strongly favored . indeed , we find that negative @xmath20 is only possible for very large values of @xmath18 . conversely , if @xmath20 is positive the new supersymmetric contribution can help to explain this possible discrepancy between the sm prediction and experiment .     as a function of @xmath18 for several ranges of @xmath19 , and @xmath101 . the spread of points come from scanning over the acceptable input values of @xmath14 and @xmath15 . the red points indicate @xmath102 , the green points @xmath103 , the blue points @xmath104 , and the magenta points @xmath105 . , scaledwidth=70.0% ]    the value of @xmath106 is shown as a function of @xmath18 in fig . [ g2-mu ] . in generating this figure , we have taken @xmath101 , and have scanned over input values of @xmath14 and @xmath15 at @xmath11 . the distribution for @xmath107 looks the same , except the sign of @xmath108 is opposite . with @xmath109 , the new physics contribution is frequently too large , and from this we obtain a lower bound on @xmath18 as a function of @xmath19 . for @xmath110 , this bound is @xmath111 , while for @xmath112 , it increases to @xmath113 .       plane of solutions that respect the bounds of @xmath114 and @xmath115 . due to uncertainty in the top quark mass , and the theoretical uncertainty in the computation of @xmath116 , a more conservative constraint on this theoretically computed value of @xmath116 is @xmath117 , which is also shown in the figure.,scaledwidth=70.0% ]    a further constraint on hens models , and one we have not yet imposed , is that the sm higgs boson mass should exceed the lep  ii bound  @xcite , m_h > 114.4  . this bound also applies to the lightest cp - even higgs boson in much of the parameter space of the mssm . however at tree - level in the mssm , the lightest cp - even higgs boson has a mass below @xmath118 . it is only because of large loop corrections to the mass , predominantly due to the scalar tops , that this higgs state can be raised above the lep  ii bound . with vanishing input scalar soft masses , the stop masses scale with @xmath18 . the higgs boson mass bound therefore imposes a further lower bound on the universal input gaugino mass . the combined bounds on @xmath18 as a function of @xmath19 from the conditions @xmath119 and @xmath120  gev are shown in fig . [ tanb - m12 ] . we impose a slightly weaker @xmath117 lower bound on the higgs boson mass than the @xmath121 lep  ii bound to account for various uncertainties associated with the theoretical computation of @xmath116 . we have taken @xmath122 in our analysis . at smaller @xmath19 , less than about 15 , the higgs mass bound imposes the stronger constraint , while the upper bound on @xmath75 is more significant for values of @xmath123 . for any value of @xmath19 , @xmath18 must be greater than about @xmath124  gev if we impose the weaker higgs mass bound ( @xmath125  gev ) , and larger than about @xmath126  gev to satisfy the stronger bound ( @xmath127  gev ) . note that as @xmath18 grows , the phenomenological constraints on the model tend to weaken , but usually at the cost of increased fine - tuning in the higgs sector  @xcite . in the previous section , we found that in a large region of the hens parameter space a slepton or a sneutrino is the lsp . such an lsp can be problematic for cosmology . if the lsp is a charged slepton , the very strong constraints that exist for charged stable particles imply that such a scenario is all but ruled out  @xcite . these bounds do not apply to a sneutrino lsp , but in this case the direct detection rate is much too high ( for a mass of @xmath128 )  @xcite . without invoking some additional and interesting mechanisms that allow the sneutrino as a more viable lsp  @xcite , we will focus on the case of a neutralino lsp . also , a slepton as the lightest superpartner particle , charged or not , may still provide a consistent picture of dark matter if the gravitino is the lsp  @xcite . we will comment briefly on that possibility later . we investigate the relic density of neutralino lsps at various points in the allowed parameter space with the aid of darksusy  4.1  @xcite . this computer program performs a fully relativistic computation of the relic density , and includes all relevant coannhilation channels . figures  [ 10 - 300 ] and [ 10 - 500 ] show the neutralino lsp relic density for @xmath110 , @xmath129  gev and @xmath126  gev , and @xmath130 for the full range of allowed input values of @xmath14 and @xmath15 at @xmath49 . in both figures the black plus signs indicate the regions in which the lightest neutralino is not the lsp , but that are otherwise allowed . the red triangles correspond to parameter points where the neutralino relic density is acceptably small , @xmath131 . this is to be compared with the observed dark matter density  @xcite , h^2 = 0.1045^+0.0072_-0.0095  ( ) . in the blue , green , and magenta regions , the neutralino relic density exceeds @xmath132 . these regions can still be consistent with the wmap measurements if there is a late - time injection of entropy into the universe after the neutralinos have frozen out  @xcite .    , @xmath129  gev , and @xmath133 . the region in which the lightest neutralino is not the lsp is denoted by the black plus signs . the red triangles indicate parameter points where the neutralino lsp relic density is less than @xmath131 . in the blue and green regions , the neutralino lsp relic density exceeds this value.,scaledwidth=70.0% ]    , @xmath134  gev , and @xmath133 . the region in which the lightest neutralino is not the lsp is denoted by the black plus signs . the red triangles indicate parameter points where the neutralino lsp relic density is less than @xmath131 . in the blue , green , and magenta regions , the neutralino lsp relic density exceeds this value.,scaledwidth=70.0% ]    the shape of the neutralino relic density contours in figs .  [ 10 - 300]-[10 - 500 ] can be understood in terms of the mass spectrum of the model . in most of the parameter space , the lightest neutralino is predominantly bino . the main annihilation channels in this bulk region are @xmath135-channel slepton exchanges . this is not efficient enough to reduce the relic density to an acceptable level for the values of @xmath18 that are relevant , although it does come close for @xmath129  gev .    along the left and right edges of the neutralino region , the mass of the neutralino lsp approaches that of the lightest slepton . this near degeneracy allows for coannihilation between the neutralino lsp and the lightest slepton to become effective , pushing the neutralino relic density to a value well below the wmap value . moving away from these edges towards the bulk region , the coannihilation efficiency falls off quickly , roughly as @xmath136 $ ] , and the neutralino density goes up . in this transitional region , where slepton coannihilation is only moderately efficient , the correct dark matter density is obtained . the strip of low relic density along the top of the neutralino lsp region arises because the @xmath9 parameter becomes small . in this strip , the neutralino lsp develops a significant higgsino component allowing it to annihilate effectively through gauge bosons , and by coannihilation with the lightest chargino .    , @xmath134  gev , and @xmath133 . the region in which the lightest neutralino is not the lsp is denoted by the black plus signs . the red triangles indicate parameter points where the neutralino lsp relic density is less than @xmath131 . in the blue , green , and magenta regions , the neutralino lsp relic density exceeds this value.,scaledwidth=70.0% ]    in the regions where the lightest neutralino is not the lightest sm superpartner ( denoted by black plus signs in figs . [ 10 - 300]-[10 - 500 ] ) the lightest superpartner is always a slepton . on the left - hand side of the neutralino region , this particle is either a tau or an electron sneutrino , as illustrated in figs . [ lsp-10 - 300]-[lsp-30 - 500 ] . on the right , the lightest superpartner is a mostly right - handed stau or selectron . the annihilation of sleptons is very efficient in the early universe . if such a particle were stable , the relic density in the regions discussed above would be on the order of @xmath137 . a relic density of heavy charged particles of this size is firmly ruled out by direct searches  @xcite . even for a stable sneutrino , a relic density of this size is ruled out by dark matter direct detection searches  @xcite . a charged or neutral slepton lighter than the lightest neutralino may still be acceptable provided the gravitino is the true lsp . since the gravitino couples very weakly to the mssm states , the slepton nlsp would freeze out as if it were the lsp , and decay into gravitinos at a much later time . the final gravitino density produced by these decays is determined by the quasi - stable nlsp density , @xmath138 , through the relation  @xcite _ 3/2^decay h^2 = _ h^2 , where @xmath24 is the gravitino mass . in the parameter regions we are considering , this density is too small to account for all the dark matter if nlsp decays are the only source of relic gravitinos . however , there are other possible sources of relic gravitinos , such as thermal production after inflationary reheating  @xcite and non - thermal production through heavy particle decays  @xcite that can bring the total gravitino relic density up to the value needed to explain all the dark matter . let us also note that this scenario is constrained by the requirement that the late - time decays not overly disrupt the predictions of big - bang nucleosynthesis or the black - body spectrum of the cosmic microwave background radiation . these constraints are relatively weak for a sneutrino nlsp , but they are quite severe for a charged slepton ( or neutralino ) nlsp , and require @xmath139  mev for most of the range of nlsp masses we are considering  @xcite .    we have also examined the effect of varying @xmath19 on the predictions for dark matter within the model . smaller values of this ratio , @xmath140 , do not change the qualitative features of the picture described above . for @xmath141 , there are a couple of important changes . most importantly , larger values of @xmath19 induce more mixing between the left- and right - handed staus , which has the effect of lowering the mass of the lightest stau . because of this , for @xmath112 and @xmath134  gev there is no longer an acceptable region of parameter space in which the lightest neutralino is both the lightest superpartner , and mostly higgsino . in fig . [ 30 - 500 ] we plot the neutralino lsp relic density for @xmath142 , @xmath143 , and @xmath133 . the thin slice of acceptable @xmath144 arises due to the coannihilation of the lsp with a light slepton . the prospects for direct and indirect detection of neutralino dark matter were investigated using darksusy  4.1  @xcite . for the most part , the direct and indirect detection signals within our scenario are very similar to those of a generic msugra model with a mostly bino lsp  @xcite . in general , these potential signals are very weak . however , much stronger signals can arise when the neutralino lsp has a significant higgsino component .     and @xmath134  gev . the black plus signs indicate the parameter region that is consistent with various phenomenological constraints , but need not have a neutralino lsp . the red , green , blue , magenta points indicate parameter points for which a neutralino is the lsp , for several ranges of @xmath145.,scaledwidth=70.0% ]    dark matter in the local halo can be detected directly by its elastic scattering with heavy nuclei . the most strongly constrained neutralino - nucleus cross - sections are the spin - independent ones . it is conventional to express the experimental limits on these cross - sections in terms of an effective neutralino - proton cross - section . the values of the effective spin - independent cross - sections in the present model , for @xmath110 and @xmath18 = 500  gev , are shown in fig . [ dd-10 - 500 ] .. ] except in a thin strip at the top of the allowed region , where the neutralino lsp is predominantly higgsino , these cross - sections are much smaller than the current experimental bound ( for a standard set of assumptions about the local halo density ) of @xmath146  pb  @xcite for the range of neutralino masses we consider here . the scattering cross - sections in the higgsino region are within an order of magnitude this bound .     and @xmath129 ,  500 , and 700  gev , as well as for @xmath112 and @xmath147 , as a function of the ratio @xmath148 . the current experimental limit for standard assumptions about the local halo density is @xmath146  pb for the range of neutralino masses we consider here  @xcite . , scaledwidth=70.0% ]    spin - independent scattering between a neutralino and a nucleon is mediated predominantly by the exchange of cp - even higgs bosons and squarks . in the allowed parameter regions discussed above , the squarks tend to be much heavier than the neutralino lsp , thereby suppressing their contribution . thus , the leading contribution to the spin - independent neutralino - nucleon cross - section usually comes from cp - even higgs exchange . since the neutralino higgs vertices are proportional to the higgsino component of the neutralino , the effective cross - section depends sensitively on the ratio @xmath148 . this is illustrated in fig . [ dd - mu - m1 ] for @xmath110 and @xmath149  gev , as well as for @xmath112 and @xmath147 . the dependence on other parameters such as @xmath150 and @xmath151 is much weaker .     and @xmath134  gev . a detector threshold of 1gev is assumed . the best current bound is @xmath152 coming from super - kamiokande  @xcite . future sensitivities from icecube and antares are @xmath153 . , scaledwidth=70.0% ] relic neutralinos can also be searched for indirectly by looking for their annihilation products in regions where they tend to clump , and have a local density much larger than the average value . in these particularly dense patches , the rate of neutralino annihilation can become large enough that their products are potentially observable . the most stringent of these indirect detection constraints on neutralino dark matter usually comes from their annihilation in the core of the sun and the earth .- channel cp - odd higgs resonance . ] the neutrinos produced by this process can lead to a signal , in the form of a muon flux , in neutrino telescopes . the best current bound on such a muon flux comes from the super - kamiokande experiment  @xcite , and is on the order of @xmath152 . this sensitivity or bound is expected to be tightened to @xmath154 in the next few years by icecube  @xcite and antares  @xcite . the values of @xmath155 due to annihilation in both the core of the earth and the sun in the present model with @xmath110 and @xmath134  gev are shown in fig . [ muflux ] as a function of the ratio @xmath148 , assuming a detector threshold of @xmath156 . as for the direct detection signal , the largest indirect detection signal is obtained when @xmath148 is on the order of unity and the neutralino lsp has a significant higgsino component . in fact , for @xmath157 , the signal as at or slightly above the super - kamiokande bound . for larger values of @xmath148 the signal falls off very quickly to values that are well below the reach of upcoming experiments . in hens scenarios , the sleptons and the electroweak gauginos are generally very light relative to the squarks and the gluino . if the lightest neutralino is the lsp , which we assume throughout this section , the distinguishing feature of these scenarios at colliders are multi - lepton events with missing @xmath158 . in this section we discuss the prospects for discovery and identification of hens models at the tevatron and the lhc . the most promising search channel at the tevatron is the trilepton signal with missing @xmath158  @xcite . this can be induced , for example , by the electroweak production of @xmath159 , with subsequent cascades of the form @xmath160 and @xmath161 . for @xmath162 , the significant source of susy events comes from the electroweak production of gauginos , making this channel a copious and clean one . in hens scenarios , the @xmath163 and @xmath164 states tend to be mostly wino and have two - body decays into left - handed sleptons . because of this feature , the branching fractions of the abovementioned decay cascades can be significant , leading to a sizeable trilepton cross - section . indeed , the mass spectrum derived from hens models is close to being optimal for trilepton production .    to estimate the effective tevatron trilepton cross - sections , we have simulated susy production from @xmath165 collisions at @xmath166  tev using isajet  7.74  @xcite . following the treatment in ref . @xcite , we use the isajet subroutines calsim and calini ( in the isaplt package ) as a simple detector model with coverage in the range @xmath167 , and calorimeter cells of size @xmath168 . to simulate energy resolution uncertainties , the electromagnetic calorimeter cells are smeared by an amount @xmath169 , while the hadronic calorimeter cells are smeared by an amount @xmath170 . we define jets as hadronic clusters with @xmath171  gev within a cone of size @xmath172 , and use the getjet subroutine to perform the clustering . isolated leptons are defined to be @xmath173 s or @xmath9 s having @xmath174  gev , with net visible hadronic activity @xmath175  gev within a cone of size @xmath176 about the lepton direction . we focus on a particular set of cuts , corresponding to the hc2 set in ref . @xcite , that is well - suited to the hens mass spectrum  @xcite . in each event , we require three isolated leptons with @xmath177 , and @xmath178 . in addition to this , the total missing @xmath158 must exceed @xmath179  gev , the invariant mass of same - flavor opposite - sign dileptons must lie in the range @xmath180 , and the transverse invariant mass between each lepton and the missing @xmath158 vector must lie outside the range @xmath181 . the dilepton invariant mass veto is designed to remove background events from off - shell @xmath182 and @xmath183 decays , while the @xmath184 veto removes leptons from @xmath23 decays . with these cuts , the sm background is estimated to be @xmath185  @xcite , and is due mostly to the remaining @xmath186 and @xmath187 events in which both off - shell gauge bosons decay leptonically .     and @xmath110 . the estimated background is @xmath188 , scaledwidth=70.0% ]    in fig . [ tevscan ] we show the trilepton cross - section subject to the cuts for @xmath129  gev and @xmath110 . this value of @xmath18 is about as small as possible within the model given the lower bound on the light higgs boson mass , and represents a best - case scenario at the tevatron . note that for considerably larger values of @xmath19 , the constraint from the anomalous magnetic moment of the muon requires larger values of @xmath18 as well , as can be seen in fig . [ tanb - m12 ] . like in the previous plots , the values of @xmath14 and @xmath15 in fig . [ tevscan ] are those at the input scale , @xmath30 .    the dependence of the trilepton cross - section on @xmath14 and @xmath15 can be understood in terms of the mass spectrum . except in the upper - right portion of the allowed parameter space , the effective cross - section increases smoothly from bottom to top as the value of @xmath9 decreases . in most of the parameter space , @xmath9 is larger than @xmath189 and the @xmath163 and @xmath190 states are mostly wino . as @xmath9 approaches @xmath189 , these states develop a larger higgsino fraction and their masses are reduced by the mixing . the heavier chargino and neutralino states become lighter as well . on account of these effects , the total gaugino cross section is increased leading to more trilepton events . this pattern is broken in the upper right corner of the parameter space because the mass of the @xmath163 state approaches the left - handed slepton masses from above , again due to higgsino mixing . when this mass difference becomes small , the branching fraction for @xmath191 goes down . the leptons produced by the cascades become relatively soft as well . since this decay mode plays a prominent role in the trilepton signal subject to the hc2 cuts , the effective cross - section falls off rapidly when the decay fraction is suppressed . the effective cross - section in this region can be increased by using slightly weaker lepton @xmath192 cuts , such as the sc2 set discussed in ref . @xcite , but at the expense of an increase in background . the effective trilepton cross - sections shown in fig . [ tevscan ] fall within the range of @xmath193 . given the estimated background of @xmath194 , the signal significance level is marginal . for example , the poisson probability @xmath195 for a total of ten events , corresponding to the maximal expected signal and background with @xmath196 , is about @xmath197 . while this is unfortunately not enough for a discovery , an excess of clean trilepton events at the tevatron would provide a tantalizing hint of a light hens scenario . we also note that other event signatures involving leptons can be searched for in these scenarios . of particular noteworthiness is the same - sign dilepton signature , which has small standard model background . if nature is supersymmetric and has a hens spectrum , the prospects for discovery at the lhc with @xmath198 of data are excellent provided @xmath18 is less than about 700  gev . to quantify this , we focus on six inclusive lhc susy search channels , classified by the number of isolated leptons in the event : @xmath199 ; @xmath200 ; @xmath201 ; @xmath202 ; @xmath203 ; @xmath204  @xcite . ( here , @xmath205 and @xmath206 refer to opposite - sign and same - sign dileptons , respectively . ) besides an excess of events in these channels , which is expected in many susy scenarios , the relative numbers of events within different channels can point towards small input scalar soft masses . supersymmetric events at the lhc were simulated using isajet  7.74  @xcite . we use the isajet subroutines calsim and calini ( in the isaplt package ) as a simple detector model with coverage in the range @xmath207 , and calorimeter cells of size @xmath208 . a gaussian smearing of the calorimeter cells is included to simulate energy resolution uncertainties . the electromagnetic calorimeter cells are smeared by an amount @xmath209 , where @xmath210 denotes addition in quadrature . hadronic calorimeter cells are smeared by an amount @xmath211 for @xmath212 , and @xmath213 for @xmath214 . we define jets as clusters with @xmath215  gev and @xmath212 within a cone of size @xmath172 , and use the getjet subroutine to perform the clustering . isolated leptons are defined to be @xmath173 s or @xmath9 s having @xmath216  gev and @xmath217 , with total visible activity @xmath218  gev within a cone of size @xmath219 about the lepton direction .    for all channels studied , we choose a cut energy @xmath220 and demand that each event have at least two hard jets , @xmath221 , with @xmath222 , as well as missing transverse energy @xmath223 . this cut substantially reduces the sm backgrounds relative to the susy signals . would be preferable to reduce the large sm backgrounds in the @xmath224 channel . however , the @xmath225 susy signal is still easily distinguishable from the large background for the parameter points we consider here . ] we also require that the transverse sphericity of the event satisfies @xmath226 to reduce the dijet background  @xcite . in zero - lepton events , we demand that the transverse angle between the missing momentum vector and the nearest jet must lie in the range @xmath227 . in the one - lepton channel , we require a single isolated lepton with @xmath228 , as well as @xmath229 to reduce the leptonic @xmath23 background . for events with two or more isolated leptons , we demand that @xmath230 for the two hardest leptons .     and @xmath110 for the five sample points described in the text . for comparison , the sm backgrounds are estimated to be about @xmath231 , @xmath232 , @xmath233 , @xmath234 , @xmath235 , and @xmath236 for the @xmath225 , @xmath237 , @xmath238 , @xmath239 , @xmath240 and @xmath241 channels respectively  @xcite.,scaledwidth=70.0% ]    the cross sections after cuts for @xmath242 and @xmath110 are given in fig . [ lhcbar ] for five sample points . for comparison , the sm backgrounds are estimated to be about @xmath243 , @xmath244 , @xmath245 , @xmath246 , @xmath247 , and @xmath248 for the @xmath225 , @xmath237 , @xmath238 , @xmath239 , @xmath240 , and @xmath241 channels respectively  @xcite . the locations of the sample points , @xmath249 and @xmath250 , in the @xmath251 plane are listed in the appendix , and are also indicated in figs .  [ 10 - 500-scan-3l ] and [ 10 - 500-scan-1l ] . among the five sample points , @xmath8 and @xmath252 have a neutralino relic density within the wmap allowed range , while the other points lead to relic densities that are too large ( but could be acceptable with a non - standard cosmology ) . at point e , the @xmath9 term is on the same order as @xmath253 , but it is greater than @xmath254 at the other sample points . thus , except for point e , the lsp is a mostly bino neutralino , while the lightest chargino and the next - to - lightest neutralino are predominantly wino . at point e where @xmath255 , all the chargino and neutralino states are fairly light and have significant higgsino components , which , as we shall discuss below , is the reason for the increase in the @xmath240 and @xmath241 rates . cross - sections after cuts at the lhc for @xmath256 and @xmath110 . the estimated background is @xmath247.,scaledwidth=70.0% ]    in each of the six search channels , the susy signal is easily distinguishable from the background with @xmath257 of luminosity at the lhc . a more challenging task beyond an initial discovery is to distinguish this class of models from other ( susy ) scenarios and to deduce the model parameters . the number of leptonic events relative to the number of @xmath224 events is useful in this regard . compared to a generic msugra input spectrum with @xmath258 , the ratio of @xmath259 events to @xmath224 events is much larger for a given value of @xmath18 . for example , in msugra with @xmath260 , the ratio of @xmath261 to @xmath259 events is greater than four , whereas this ratio is close to unity for all five sample points considered . the ratio of the number of @xmath224 events to the number of @xmath262 events is also much larger in a generic msugra framework than it is here . this is the consequence of having left - handed sleptons lighter than the @xmath163 and @xmath164 states , which are in turn light enough to be generated by squark decays . for example , cascade chains such as @xmath263 have a significant branching probability , and are a rich source of leptons . the dependence of the effective @xmath240 cross - section on the input higgs soft mass parameters is shown in fig . [ 10 - 500-scan-3l ] . for the most part , this dependence is fairly mild except in the upper right portion of the allowed region . here , the @xmath9 term approaches the bino mass @xmath64 , and in the thin tail extending to the right , @xmath9 even falls below @xmath64 . in this region , all the neutralinos and charginos are significantly lighter than the squarks and gluinos . as a result , the decay cascades initiated by the strong superpartners are frequently very long , involving several chargino and neutralino states . at each step in the cascade chain there is a chance of producing a lepton , and thus the total fraction of events containing multiple leptons is very high . for example , the decay chain @xmath264 is kinematically allowed when @xmath9 is small , and has a significant branching fraction . the preponderance of leptons can be so high that the number of @xmath225 and @xmath237 events ( and even to some extent some @xmath265 events ) are significantly suppressed . this can be seen in fig . [ 10 - 500-scan-1l ] , which shows the @xmath237 effective cross section for @xmath147 and @xmath110 . note that the small @xmath9 region is strongly constrained by direct and indirect searches for dark matter , and will be probed by upcoming experiments , as was discussed above . cross - sections after cuts at the lhc for @xmath256 and @xmath110 . the estimated background is @xmath244.,scaledwidth=70.0% ]    in the leftmost portion of the allowed region of fig . [ 10 - 500-scan-3l ] , there is also a net decrease in the cross section , which occurs in the other leptonic channels as well . within this region , leptons typically originate from decays of the mostly wino @xmath163 and @xmath164 states into left - handed sleptons and sneutrinos , which subsequently decay into the neutralino lsp . however , these left - handed states are only slightly heavier than the lsp , so the lepton emitted from the slepton decays tends to be soft , making it less likely to pass the lepton @xmath192 cuts . a particularly distinctive signature of the hens models are inclusive @xmath241 events . we find effective cross - sections above @xmath266 for @xmath110 and @xmath147 , which is sufficient for a @xmath196 lhc discovery given the sm background of about @xmath236  @xcite . there is a sharp increase in the @xmath241 cross - section in the small @xmath9 region at the upper right of the parameter space . the dominant sources of this increase are cascades initiated by right - handed squarks of the type described previously . furthermore , because the left - handed sleptons are lighter than @xmath267 but heavier than @xmath268 and @xmath269 in this region , superpartner cascades such as @xmath270 accompanied by many leptons have a non - trivial branching fraction and can produce three leptons from the single squark parent . is very small in this part of the parameter space . however , the other two leptons in the cascade tend to be quite hard . ] as a result , @xmath241 rates greater than @xmath271 can occur . we have also investigated the exclusive clean trilepton channel . it does not appear to be as promising as the inclusive channels .     and @xmath112 for the five sample points described in the text . for comparison , the sm backgrounds are estimated to be about @xmath231 , @xmath232 , @xmath233 , @xmath234 , @xmath235 , and @xmath236 for the @xmath225 , @xmath237 , @xmath238 , @xmath239 , @xmath240 and @xmath241 channels respectively  @xcite.,scaledwidth=70.0% ]    varying @xmath19 does not qualitatively affect our findings . the cross sections after cuts for @xmath242 and @xmath112 are given in fig . [ lhcbar30 ] for five sample points , @xmath272 . details of these sample points are given in the appendix . the cross sections in all six channels are similar to those in fig . [ lhcbar ] with @xmath110 . in particular , the ratio of @xmath225 to @xmath237 events is still close to unity , and the @xmath240 and @xmath241 rates are observably large . the main difference that occurs at larger values of @xmath19 is that there is no small @xmath9 region . since the entire mass spectrum in hens models scales with @xmath18 , so too do the event rates . we have checked that for @xmath18 as large @xmath273 , corresponding to a gluino mass of @xmath274 , the inclusive event rates in all channels other than the @xmath225 and @xmath241 are large enough that a discovery with @xmath275 of lhc data is feasible . on the other hand , the event rates become even larger for smaller values of @xmath18 , making discovery even easier . supersymmetry has been recognized as a viable theory of physics beyond the standard model for many years now . it was quickly realized that it was not only viable , but also potentially useful in the quest to understand stability of the electroweak potential , radiative electroweak symmetry breaking , grand unification , dark matter , and baryogenesis . in subsequent years , there has been much effort devoted to understanding how supersymmetry breaking is to be achieved without creating additional phenomenological problems , such as too large fcnc . there are two particularly simple alternatives that keep the good features of supersymmetry while ( mostly ) dismissing the bad features . one approach is to raise the scalar masses significantly higher than the supersymmetric fermion masses . this is the idea of split supersymmetry discussed in the introduction . one drawback of this scenario is the apparent finetuning in the electroweak sector . the approach we pursue in this article is in some sense the opposite of split supersymmetry . here , rather than introduce a huge hierarchy of scalar masses over fermion masses , we wish to zero out the superpartner scalar masses at some scale ( i.e. ,  splat supersymmetry " ) . the simplest model of all scalar masses having a zero boundary condition does not work . however , applying a small alteration to the most minimal idea , namely that the higgs bosons are exempt from zero boundary condition requirement , preserves the good features of these theories , while satisfying the phenomenological requirements described in the text . this idea of higgs exempt no - scale ( hens ) supersymmetry has many phenomenological implications worthy of consideration at current and future experimental facilities . for example , we have found that the scenario can accommodate the tantalizing ( but small ) deviation of @xmath276 of the muon compared to the sm prediction . it also suggests a near maximal leptonic signal for the tevatron , and thus provides an excellent benchmark theory for the tevatron to either discover this form of supersymmetry or rule out large regions of parameter space in a clean way . furthermore , the lhc signatures are of many multi - lepton events . perhaps the most distinctive of them is the inclusive @xmath241 channel which can effectively rule out hens models up to gaugino mass scales that are uncomfortably large from the normal finetuning point of view . for the most part , this form of supersymmetry is rather straightforward for the lhc to find . an important exception is the lightest higgs boson , whose mass is pressured in this scenario to be low , and thus perhaps close to the current bound of @xmath121 . given the difficulties of finding a higgs boson less than @xmath277  @xcite , discovering the higgs boson might be one of the more challenging steps in confirming the complete structure of this theory . * acknowledgements *    we would like to thank p. kumar for discussions , and for contributions at the early stages of this work . we also wish to thank g. kane , s. martin , a. pierce and s. thomas for helpful discussions . this work is supported in part by the department of energy and the michigan center for theoretical physics . in this appendix , we list the relevant properties of the sample points @xmath278 chosen for @xmath110 and @xmath242 . the locations of these points in the @xmath279 plane are shown in figs . [ 10 - 500-scan-3l ] and [ 10 - 500-scan-1l ] . we also list properties of the points @xmath280 corresponding to @xmath112 and @xmath147 . .model parameters and particle masses for sample points @xmath278 , all with @xmath110 and @xmath147 . all dimensionful quantities in the table are listed in gev units . the @xmath144 values are valid computations for the assumption of standard thermal cosmological evolution and stable lightest neutralino . viability of points @xmath17 and @xmath16 require alterations to the standard assumptions . [ 10 - 500table ] [ cols="^,^,^,^,^,^",options="header " , ]      for reviews , see for example h.  e.  haber and g.  l.  kane , phys . * 117 * , 75 ( 1985 ) ; s.  p.  martin , hep - ph/9709356 ; d.  j.  h.  chung et al . , phys . * 407 * , 1 ( 2005 ) [ hep - ph/0312378 ] ; m.  a.  luty , hep - th/0509029 . s.  dimopoulos and h.  georgi , nucl . b * 193 * , 150 ( 1981 ) . s.  dimopoulos , s.  raby and f.  wilczek , phys . d * 24 * , 1681 ( 1981 ) . see for example , f.  gabbiani , e.  gabrielli , a.  masiero and l.  silvestrini , nucl . b * 477 * , 321 ( 1996 ) [ hep - ph/9604387 ] , m.  misiak , s.  pokorski and j.  rosiek , adv . high energy phys . * 15 * , 795 ( 1998 ) [ hep - ph/9703442 ] . m.  dugan , b.  grinstein and l.  j.  hall , nucl . b * 255 * , 413 ( 1985 ) . m.  leurer , y.  nir and n.  seiberg , nucl . b * 398 * , 319 ( 1993 ) [ hep - ph/9212278 ] . y.  nir and n.  seiberg , phys . b * 309 * , 337 ( 1993 ) [ hep - ph/9304307 ] . m.  leurer , y.  nir and n.  seiberg , nucl . b * 420 * , 468 ( 1994 ) [ hep - ph/9310320 ] . m.  dine , r.  g.  leigh and a.  kagan , phys . d * 48 * , 4269 ( 1993 ) [ hep - ph/9304299 ] . l.  j.  hall and h.  murayama , phys . lett .   * 75 * , 3985 ( 1995 ) [ hep - ph/9508296 ] . r.  barbieri , g.  r.  dvali and l.  j.  hall , phys . b * 377 * , 76 ( 1996 ) [ hep - ph/9512388 ] . r.  barbieri , l.  j.  hall and a.  romanino , phys . b * 401 * , 47 ( 1997 ) [ hep - ph/9702315 ] . for a review , see g.  f.  giudice and r.  rattazzi , phys .  rept .   * 322 * , 419 ( 1999 ) [ hep - ph/9801271 ] , and references therein . l.  randall and r.  sundrum , nucl . b * 557 * , 79 ( 1999 ) [ hep - th/9810155 ] . g.  f.  giudice , m.  a.  luty , h.  murayama and r.  rattazzi , jhep * 9812 * , 027 ( 1998 ) [ hep - ph/9810442 ] . n.  arkani - hamed and s.  dimopoulos , jhep * 0506 * , 073 ( 2005 ) [ hep - th/0405159 ] . g.  f.  giudice and a.  romanino , nucl . b * 699 * , 65 ( 2004 ) [ erratum - ibid . b * 706 * , 65 ( 2005 ) ] [ hep - ph/0406088 ] . n.  arkani - hamed , s.  dimopoulos , g.  f.  giudice and a.  romanino , nucl . b * 709 * , 3 ( 2005 ) [ hep - ph/0409232 ] . see also a.  pierce , phys . d * 70 * , 075006 ( 2004 ) [ hep - ph/0406144 ] . a.  arvanitaki and p.  w.  graham , phys . d * 72 * , 055010 ( 2005 ) [ hep - ph/0411376 ] . a.  masiero , s.  profumo and p.  ullio , nucl . b * 712 * , 86 ( 2005 ) [ hep - ph/0412058 ] . b.  thomas , phys . d * 72 * , 023519 ( 2005 ) [ hep - ph/0503248 ] . n.  arkani - hamed , a.  delgado and g.  f.  giudice , nucl .  phys . b * 741 * , 108 ( 2006 ) [ hep - ph/0601041 ] . u.  chattopadhyay , d.  das , p.  konar and d.  p.  roy , hep - ph/0610077 . m.  ibe , t.  moroi and t.  t.  yanagida , hep - ph/0610277 . r.  mahbubani and l.  senatore , phys . d * 73 * , 043510 ( 2006 ) [ hep - ph/0510064 ] . d.  e.  kaplan , g.  d.  kribs and m.  schmaltz , phys . d * 62 * , 035010 ( 2000 ) [ hep - ph/9911293 ] ; z.  chacko , m.  a.  luty , a.  e.  nelson and e.  ponton , jhep * 0001 * , 003 ( 2000 ) [ hep - ph/9911323 ] . for a review , see a.  b.  lahanas and d.  v.  nanopoulos , phys . * 145 * , 1 ( 1987 ) ; a.  b.  lahanas , cern - th-7092 - 93 _ lectures given at international school of subnuclear physics : 31th course : from supersymmetry to the origin of space - time , erice , italy , 4- 12 jul 1993 _    m.  a.  luty and r.  sundrum , phys . d * 65 * , 066004 ( 2002 ) [ hep - th/0105137 ] . m.  luty and r.  sundrum , phys . d * 67 * , 045007 ( 2003 ) [ hep - th/0111231 ] . m.  ibe , k.  i.  izawa , y.  nakayama , y.  shinbara and t.  yanagida , phys . d * 73 * , 015004 ( 2006 ) [ hep - ph/0506023 ] . m.  ibe , k.  i.  izawa , y.  nakayama , y.  shinbara and t.  yanagida , phys . d * 73 * , 035012 ( 2006 ) [ hep - ph/0509229 ] . m.  schmaltz and r.  sundrum , hep - th/0608051 . m.  schmaltz and w.  skiba , phys . d * 62 * , 095005 ( 2000 ) [ hep - ph/0001172 ] . m.  schmaltz and w.  skiba , phys . d * 62 * , 095004 ( 2000 ) [ hep - ph/0004210 ] . d.  e.  kaplan and t.  m.  p.  tait , jhep * 0006 * , 020 ( 2000 ) [ hep - ph/0004200 ] . w.  buchmuller , j.  kersten and k.  schmidt - hoberg , jhep * 0602 * , 069 ( 2006 ) [ hep - ph/0512152 ] . s.  komine and m.  yamaguchi , phys . d * 63 * , 035005 ( 2001 ) [ hep - ph/0007327 ] . c.  balazs and r.  dermisek , jhep * 0306 * , 024 ( 2003 ) [ hep - ph/0303161 ] . w.  buchmuller , l.  covi , j.  kersten and k.  schmidt - hoberg , [ hep - ph/0609142 ] . for a recent discussion of negative values of @xmath281 in msugra , see : j.  l.  feng , a.  rajaraman and b.  t.  smith , phys . d * 74 * , 015013 ( 2006 ) [ hep - ph/0512172 ] . e.  cremmer , s.  ferrara , c.  kounnas and d.  v.  nanopoulos , phys . b * 133 * , 61 ( 1983 ) . j.  r.  ellis , a.  b.  lahanas , d.  v.  nanopoulos and k.  tamvakis , phys . b * 134 * , 429 ( 1984 ) . j.  r.  ellis , c.  kounnas and d.  v.  nanopoulos , nucl . b * 241 * , 406 ( 1984 ) . j.  r.  ellis , c.  kounnas and d.  v.  nanopoulos , nucl . b * 247 * , 373 ( 1984 ) . see , for example , n.  weiner , hep - ph/0106097 ; c.  csaki , g.  d.  kribs and j.  terning , phys . d * 65 * , 015004 ( 2002 ) [ hep - ph/0107266 ] . e.  witten , phys . b * 155 * , 151 ( 1985 ) . g.  camara , l.  e.  ibanez and a.  m.  uranga , nucl . b * 689 * , 195 ( 2004 ) [ hep - th/0311241 ] . k.  choi , a.  falkowski , h.  p.  nilles and m.  olechowski , nucl . b * 718 * , 113 ( 2005 ) [ hep - th/0503216 ] . a.  e.  nelson and m.  j.  strassler , jhep * 0009 * , 030 ( 2000 ) [ hep - ph/0006251 ] . a.  e.  nelson and m.  j.  strassler , jhep * 0207 * , 021 ( 2002 ) [ hep - ph/0104051 ] . t.  kobayashi and h.  terao , phys .  rev . d * 64 * , 075003 ( 2001 ) [ hep - ph/0103028 ] . t.  kobayashi , h.  nakano , t.  noguchi and h.  terao , phys . d * 66 * , 095011 ( 2002 ) [ hep - ph/0202023 ] . k.  r.  dienes , e.  dudas and t.  gherghetta , phys . b * 436 * , 55 ( 1998 ) [ hep - ph/9803466 ] ; k.  r.  dienes , e.  dudas and t.  gherghetta , nucl . b * 537 * , 47 ( 1999 ) [ hep - ph/9806292 ] . a.  e.  nelson and m.  j.  strassler , phys . d * 56 * , 4226 ( 1997 ) [ hep - ph/9607362 ] . s.  p.  martin and m.  t.  vaughn , phys . d * 50 * , 2282 ( 1994 ) [ hep - ph/9311340 ] . a.  djouadi , j.  l.  kneur and g.  moultaka , [ hep - ph/0211331 ] . w.  m.  yao _ et al . _ [ particle data group ] , j.  phys . g * 33 * , 1 ( 2006 ) . e.  brubaker _ [ tevatron electroweak working group ] , hep - ex/0608032 . e.  barberio _ et al . _ [ heavy flavor averaging group ( hfag ) ] , hep - ex/0603003 . see , for example , j.  a.  casas , a.  lleyda and c.  munoz , nucl . b * 471 * , 3 ( 1996 ) [ hep - ph/9507294 ] . a.  kusenko , p.  langacker and g.  segre , phys . d * 54 * , 5824 ( 1996 ) [ hep - ph/9602414 ] . m.  carena , m.  quiros and c.  e.  m.  wagner , phys . b * 380 * , 81 ( 1996 ) [ hep - ph/9603420 ] . t.  falk , k.  a.  olive , l.  roszkowski , a.  singh and m.  srednicki , phys . b * 396 * , 50 ( 1997 ) [ hep - ph/9611325 ] . r.  barate _ [ lep working group for higgs boson searches ] , phys . b * 565 * , 61 ( 2003 ) [ hep - ex/0306033 ] . d.  e.  morrissey and j.  d.  wells , phys . d * 74 * , 015008 ( 2006 ) [ hep - ph/0512019 ] . see r.  barbieri and g.  f.  giudice , nucl . b * 306 * , 63 ( 1988 ) , and references thereto . a.  gould , b.  t.  draine , r.  w.  romani and s.  nussinov , phys . b * 238 * , 337 ( 1990 ) ; a.  de rujula , s.  l.  glashow and u.  sarid , nucl . b * 333 * , 173 ( 1990 ) ; s.  dimopoulos , d.  eichler , r.  esmailzadeh and g.  d.  starkman , phys .  rev . d * 41 * , 2388 ( 1990 ) . t.  falk , k.  a.  olive and m.  srednicki , phys . b * 339 * , 248 ( 1994 ) [ hep - ph/9409270 ] . l.  j.  hall , t.  moroi and h.  murayama , phys . b * 424 * , 305 ( 1998 ) [ hep - ph/9712515 ] . n.  arkani - hamed , l.  j.  hall , h.  murayama , d.  r.  smith and n.  weiner , phys . d * 64 * , 115011 ( 2001 ) [ hep - ph/0006312 ] . d.  hooper , j.  march - russell and s.  m.  west , phys . b * 605 * , 228 ( 2005 ) [ hep - ph/0410114 ] . t.  asaka , k.  ishiwata and t.  moroi , phys . d * 73 * , 051301 ( 2006 ) [ hep - ph/0512118 ] . s.  gopalakrishna , a.  de gouvea and w.  porod , jcap * 0605 * , 005 ( 2006 ) [ hep - ph/0602027 ] .    for a nice review of these scenarios , see : j.  l.  feng , annals phys . * 315 * ( 2005 ) 2 . p.  gondolo , j.  edsjo , p.  ullio , l.  bergstrom , m.  schelke and e.  a.  baltz , jcap * 0407 * , 008 ( 2004 ) [ astro - ph/0406204 ] . d.  n.  spergel _ et al . _ , [ astro - ph/0603449 ] . for some recent examples , see g.  gelmini , p.  gondolo , a.  soldatenko and c.  e.  yaguna , phys . d * 74 * , 083514 ( 2006 ) [ hep - ph/0605016 ] . d.  e.  morrissey and j.  d.  wells , hep - ph/0606234 . d.  s.  akerib _ et al . _ , nucl . instrum . a * 559 * , 390 ( 2006 ) . j.  r.  ellis , a.  d.  linde and d.  v.  nanopoulos , phys . b * 118 * , 59 ( 1982 ) . see , for example , m.  dine , r.  kitano , a.  morisse and y.  shirman , phys . d * 73 * , 123518 ( 2006 ) [ hep - ph/0604140 ] , and references therein . see , for example , h.  baer , a.  belyaev , t.  krupovnickas and j.  ofarrill , jcap * 0408 * , 005 ( 2004 ) [ hep - ph/0405210 ] ; j.  r.  ellis , k.  a.  olive , y.  santoso and v.  c.  spanos , phys .  rev . d * 71 * , 095007 ( 2005 ) [ hep - ph/0502001 ] . s.  desai _ et al . _ [ super - kamiokande collaboration ] , phys . d * 70 * , 083523 ( 2004 ) [ erratum - ibid . d * 70 * , 109901 ( 2004 ) ] [ hep - ex/0404025 ] . p.  a.  toale [ icecube collaboration ] , [ astro - ph/0607003 ] . j.  hossl [ antares collaboration ] , _ prepared for idm 2004 : 5th international workshop on the identification of dark matter , edinburgh , scotland , united kingdom , 6 - 10 sep 2004 _    see , for example , h.  baer and x.  tata , phys . d * 47 * , 2739 ( 1993 ) ; s.  mrenna , g.  l.  kane , g.  d.  kribs and j.  d.  wells , phys . d * 53 * , 1168 ( 1996 ) [ hep - ph/9505245 ] ; v.  d.  barger , c.  kao and t.  j.  li , phys . b * 433 * , 328 ( 1998 ) [ hep - ph/9804451 ] ; e.  accomando , r.  arnowitt and b.  dutta , phys . b * 475 * , 176 ( 2000 ) [ hep - ph/9811300 ] ; v.  d.  barger and c.  kao , phys . d * 60 * , 115015 ( 1999 ) [ hep - ph/9811489 ] ; j.  d.  lykken and k.  t.  matchev , phys . d * 61 * , 015001 ( 2000 ) [ hep - ph/9903238 ] . k.  t.  matchev and d.  m.  pierce , phys .  rev . d * 60 * , 075004 ( 1999 ) [ hep - ph/9904282 ] ; k.  t.  matchev and d.  m.  pierce , phys . b * 467 * , 225 ( 1999 ) [ hep - ph/9907505 ] . h.  baer , m.  drees , f.  paige , p.  quintana and x.  tata , phys . d * 61 * , 095007 ( 2000 ) [ hep - ph/9906233 ] . f.  e.  paige , s.  d.  protopopescu , h.  baer and x.  tata , hep - ph/0312045 . h.  baer , c.  h.  chen , f.  paige and x.  tata , phys . d * 52 * , 2746 ( 1995 ) [ hep - ph/9503271 ] . h.  baer , c.  h.  chen , f.  paige and x.  tata , phys . d * 53 * , 6241 ( 1996 ) [ hep - ph/9512383 ] . atlas detector and physics performance . technical design report . 2 , cern - lhcc-99 - 15 , atlas - tdr-15 , may 1999 .
one of the most straightforward ways to address the flavor problem of low - energy supersymmetry is to arrange for the scalar soft terms to vanish simultaneously at a scale @xmath0 much larger than the electroweak scale . 
 this occurs naturally in a number of scenarios , such as no - scale models , gaugino mediation , and several models with strong conformal dynamics . 
 unfortunately , the most basic version of this approach that incorporates gaugino mass unification and zero scalar masses at the grand unification scale is not compatible with collider and dark matter constraints 
 . however , experimental constraints can be satisfied if we exempt the higgs bosons from flowing to zero mass value at the high scale . 
 we survey the theoretical constructions that allow this , and investigate the collider and dark matter consequences . 
 a generic feature is that the sleptons are relatively light . because of this 
 , these models frequently give a significant contribution to the anomalous magnetic moment of the muon , and neutralino - slepton coannihilation can play an important role in obtaining an acceptable dark matter relic density . 
 furthermore , the light sleptons give rise to a large multiplicity of lepton events at colliders , including a potentially suggestive clean trilepton signal at the tevatron , and a substantial four lepton signature at the lhc . 
 mctp-06 - 32 +    higgs boson exempt no - scale supersymmetry + and its collider and cosmology implications +    jason l. evans , david e. morrissey , james d. wells +    michigan center for theoretical physics ( mctp ) + physics department , university of michigan , ann arbor , mi 48109