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in the minimal supersymmetric extension of the standard model ( mssm ) @xcite , radiative corrections involving supersymmetric ( susy ) particles modify the tree level relation between fermion masses and their yukawa couplings @xcite . in this paper we review the sources and behavior of these susy yukawa corrections and describe their phenomenological effects . the behavior of the susy yukawa corrections is most easily derived in the context of an effective field theory ( eft ) , in which we take the low energy effective theory of the mssm below the susy scale to be a two higgs doublet model ( 2hdm ) and absorb the effects of susy radiative corrections into the parameters of the eft . at tree level , the fermion yukawa couplings and masses arise from the lagrangian , @xmath2      + { \rm h.c . } \ ] ] where we use third generation quark notation and the higgs doublets are @xmath3 the higgs vacuum expectation values ( vevs ) are constrained by @xmath4 and their ratio is parameterized by @xmath5 . the fermion masses arise from replacing the higgs fields with their vevs : @xmath6 so that @xmath7 and @xmath8 . at tree level , down - type fermions receive their masses from @xmath9 while up - type fermions receive their masses from @xmath10 . this is a consequence of the holomorphicity of the superpotential in unbroken susy ; if susy were unbroken , it would be true to all orders in the eft .    in a model with more than one higgs doublet , tree - level flavor - changing neutral higgs couplings can be eliminated if the right - handed fermion singlets with each value of hypercharge are allowed to couple to only one higgs doublet @xcite . under this requirement , called `` natural flavor conservation '' , there are two different configurations possible for the couplings of the two higgs doublets @xmath9 and @xmath10 of a 2hdm to quarks : in the type i 2hdm all the quarks couple to @xmath9 and none to @xmath10 , while in the type ii 2hdm the down - type right - handed quark singlets couple to @xmath9 while the up - type right - handed quark singlets couple to @xmath10 . the most general 2hdm without natural flavor conservation , in which the right - handed fermion singlets with each value of hypercharge couple to both higgs doublets , is called the type iii 2hdm . in unbroken susy , the higgs couplings take the form of a type ii 2hdm . however , susy must be broken in nature . when susy is broken , non - holomorphic higgs couplings to fermions arise at one loop in the eft . we first consider down - type fermions . at one loop , diagrams such as those in fig . [ fig : mssmdiags2 ]    give rise to a correction to the coupling of @xmath11 quarks to @xmath9 and a non - holomorphic coupling of @xmath11 quarks to @xmath10 : @xmath12 examining eq . [ eq : effectivel ] , we see that in the eft , the right - handed down - type quarks couple to both @xmath9 and @xmath10 . thus,_the low energy effective theory of the mssm is a type iii 2hdm_.    the @xmath11 quark mass at one loop is obtained by inserting the higgs vevs into eq . [ eq : effectivel ] : @xmath13 solving for @xmath14 we find , @xmath15 here @xmath16 because of the loop suppression . however , the third term in eq . [ eq : mbcorr ] is enhanced by a factor of @xmath0 , and thus can be quite large at large @xmath0 @xcite . this @xmath0 enhanced correction to @xmath14 has significant phenomenological consequences at large @xmath0 because it modifies the relation between @xmath14 and @xmath17 . at tree level ( so that @xmath18 ) and generate the down - type quark masses at one loop through susy breaking terms . ] at tree level , @xmath19 . at one loop , @xmath17 can be significantly smaller or larger than the tree - level value , depending on the sign of @xmath20 .    in the up - type fermion sector , an analogous calculation gives , @xmath21 in particular , there is no @xmath0 enhancement and the corrections to the relation between @xmath22 and @xmath23 are small . these corrections can still be important ; for example , they enter the mssm higgs mass calculation at the two loop level and lead to a few gev change in the upper bound on @xmath24 in some regions of parameter space @xcite . we now examine the behavior of @xmath25 as the susy mass scale is varied . it is easy to see from , e.g. , the first diagram in fig . [ fig : mssmdiags2 ] that @xmath25 are independent of @xmath26 . this diagram scales like @xmath27 , where the factor of @xmath28 comes from a helicity flip in the gluino line , the factor of @xmath29 comes from the dimensionful higgs - squark - squark coupling , and the factor of @xmath30 comes from the three - point loop integral ( here @xmath26 is the largest of the masses in the loop and we neglect external momenta ; see eq . [ eq : iabc ] ) . thus if all the soft susy breaking parameters and the @xmath29 parameter are scaled by a common factor , @xmath25 are unchanged ; i.e. , they do not decouple with @xmath26 when the ratios between susy parameters are held fixed . these susy yukawa corrections are also universal ; i.e. , they are independent of the external momenta and thus process - independent . in general , there are additional contributions to physical processes at one loop that depend on the external momenta ; however , these are suppressed by powers of @xmath31 .    although @xmath25 do not decouple with @xmath26 , they do not represent a violation of the decoupling theorem @xcite : in the limit of large pseudoscalar higgs mass @xmath32 , the effects of @xmath25 appear only in the couplings of the heavy higgs bosons , as we will now illustrate . because in the type iii 2hdm the right - handed down - type fermions couple to both higgs doublets , there is no longer a special yukawa basis for the higgs fields . we are then free to write them in a new basis chosen such that one of the doublets has zero vev ( the `` vev basis '' ) : @xmath33 where @xmath34 is the standard model ( sm ) higgs vev and we have performed the rotation ( @xmath35 ) @xmath36 note that in the vev basis @xmath37 contains the goldstone bosons while @xmath38 contains @xmath39 and @xmath40 . the two cp - even neutral higgs mass eigenstates @xmath41 and @xmath42 are given in terms of @xmath43 and @xmath44 by @xmath45 in the limit of large @xmath32 , @xmath46 goes to zero : @xmath47 so @xmath48 . thus in the limit of large @xmath32 , @xmath37 contains the goldstone bosons , the sm higgs vev , and the light higgs boson @xmath41 , while @xmath38 contains all the heavy higgs states , @xmath49 , @xmath40 and @xmath42 . the effective lagrangian in the vev basis can be written as , @xmath50 where @xmath51 and @xmath52 are the yukawa couplings in the vev basis . inserting the higgs vevs we obtain the @xmath11 quark mass : @xmath53 in particular , @xmath54 is fixed by the @xmath11 quark mass , while @xmath52 is unconstrained . thus the coupling of @xmath37 to quarks must be sm - like while that of @xmath38 is unconstrained and can contain the effects of @xmath25 . in the decoupling limit @xcite of large @xmath32 , @xmath48 so the @xmath55 coupling approaches its sm value , while the effects of @xmath25 are confined to the heavy higgs bosons in @xmath38 . we now write down the susy radiative corrections to the down - type mass - yukawa relation ( keeping only the @xmath0 enhanced contributions ) @xcite : @xmath56 where the correction @xmath57 is given by   is proportional to the product @xmath58 , it has been suggested in ref . @xcite to use the sign of @xmath57 and the sign of @xmath29 ( measured in some other process ) to determine the sign of @xmath28 and test the anomaly - mediated susy breaking scenario @xcite , which predicts a negative @xmath28 . ] @xmath59 here @xmath60 and @xmath61 is a loop integral , @xmath62/ \nonumber \\      & & [ ( a^2-b^2)(b^2-c^2)(a^2-c^2 ) ] ,      \label{eq : iabc}\end{aligned}\ ] ] which is positive for any @xmath63 and goes like @xmath64 .    solving eq . [ eq : mbyb ] for @xmath17 @xcite , we find @xmath65 where we have not expanded the denominator to one loop order . it was proven in ref . @xcite that eq . [ eq : ybmb ] includes a resummation of terms of order @xmath66 to all orders of perturbation theory . in particular , @xmath57 in eq . [ eq : ybmb ] gets no @xmath0 enhanced corrections at higher orders of the form @xmath67 . the remaining higher order corrections to @xmath57 are not @xmath0 enhanced and are thus insignificant compared to the one loop piece ( eq .  [ eq : deltab ] ) . the proof in ref . @xcite that eq . [ eq : ybmb ] receives no higher order @xmath0 enhanced contributions relies on the facts ( 1 ) that @xmath0 enters the calculation at higher orders only multiplied by @xmath14 , e.g. , from the @xmath68 term in the bottom squark mass matrix ; and ( 2 ) that no factors of @xmath69 can arise from the loop diagrams to cancel the @xmath14 factor multiplying @xmath0 , because the yukawa coupling operator is dimension four . expanding eq . [ eq : ybmb ] to one loop order , we have @xmath70 an expression of this form arises in on - shell diagrammatic one - loop calculations , in which @xmath57 enters through the @xmath11 quark mass counterterm . although eqs . [ eq : ybmb ] and [ eq : ybmb1loop ] are equivalent at one loop , they differ at higher orders : eq . [ eq : ybmb1loop ] does not contain a resummation of terms of order @xmath66 to all orders of perturbation theory . , in which the @xmath11 mass operator is renormalized , because the @xmath11 mass operator is not dimension four . see ref . @xcite for details . ] in our eft analyses in the remainder of this paper we will use eq . [ eq : ybmb ] in order to take advantage of the resummation of higher order terms . the remainder of this paper is organized as follows . we examine the effect of the susy yukawa corrections on the process @xmath71 in sec . [ sec : hbb ] and on the @xmath72 coupling in sec . [ sec : h+tb ] . in sec . [ sec : fcnceft ] we describe how flavor - changing neutral higgs interactions arise in the eft from the susy yukawa corrections , and in sec .  [ sec : fcncproc ] we summarize recent results for specific flavor changing processes . in sec . [ sec : ckm ] we discuss the renormalization of the ckm matrix . in sec . [ sec : resum ] we briefly discuss resummation of the susy yukawa corrections to flavor changing processes . finally in sec . [ sec : conclusions ] we give a summary and outlook . accurate knowledge of the @xmath71 branching ratio is important for determining the reach of the upcoming higgs searches at the tevatron and lhc @xcite . also , once a light higgs boson is discovered , precision measurements of its branching ratios ( e.g. , at a future @xmath74 linear collider ) can be used to distinguish a sm higgs boson from a mssm higgs boson in some regions of parameter space @xcite . the susy yukawa corrections can have a significant effect on these branching ratios @xcite . for example , the ratio @xmath75 is sensitive to the susy yukawa corrections to @xmath71 . coupling also receives @xmath0 enhanced susy yukawa corrections , but they are proportional to electroweak gauge couplings and are expected to be much smaller than the corrections to the @xmath55 coupling . ] at tree level , the ratio @xmath75 is the same in the sm and the mssm ( @xmath76 ) . further , in the mssm the @xmath55 and @xmath77 couplings have the same dependence on the cp - even higgs mixing angle @xmath78 , so that @xmath75 is also insensitive to the radiative corrections to @xmath78 . thus in the context of the mssm , a deviation of @xmath75 from its sm value provides a direct window onto the susy yukawa corrections @xcite . we begin by computing the susy corrections to @xmath71 in the eft approach ; that is , we assume @xmath79 and neglect the external momenta . in the next section . ] using eqs . [ eq : effectivel ] and [ eq : ybmb ] , the @xmath55 coupling is given by @xcite @xmath80      \label{eq : ghbbeft}\end{aligned}\ ] ] where the tree level coupling is @xmath81 and @xmath82 . as shown in sec . [ sec : intro ] , the susy radiative corrections to @xmath83 should decouple in the limit of large @xmath32 . indeed , we have , @xmath84 so that @xmath83 approaches its sm value as expected in the decoupling limit @xcite .      up to this point we have neglected the effects of the external momenta on @xmath71 . these give contributions of order @xmath85 , where @xmath86 . these contributions can be sizeable because of the @xmath0 enhancement , especially when the susy scale is relatively low . for example , for @xmath87 , @xmath88 is of order one even for @xmath89 tev . in order to treat the external momenta correctly , we must do an on - shell diagrammatic calculation . we focus here on the susy - qcd contributions to @xmath83 , for which diagrammatic calculations are available in refs . enhanced contributions . ] for compactness we give here an approximate formula expanded in powers of @xmath90 and @xmath91 , where we have taken @xmath92 and @xmath93 . defining @xmath94 $ ] , we have @xcite @xmath95 the first term in eq .  [ eq : dg / g ] was found before in the eft calculation ; it remains constant as @xmath96 at fixed @xmath32 . the remaining terms are neglected in the eft approach ; they decouple as @xmath96 but remain constant as @xmath97 at fixed @xmath26 . because of their @xmath30 dependence they can be identified as coming from higher dimensional operators that were neglected in our eft calculation . the correction @xmath98 decouples in the limit that both @xmath32 and @xmath96 . the susy - electroweak corrections to @xmath71 are of order @xmath99 instead of order @xmath100 and arise from the second diagram of fig . [ fig : mssmdiags2 ] . the susy - electroweak yukawa corrections are easily calculated in the eft approach ( see eq . [ eq : deltab ] ) . there are also large corrections to @xmath41 decays at order @xmath99 from the radiative corrections to the cp - even higgs mixing angle @xmath78 @xcite . these corrections are usually taken into account by inserting the radiatively corrected value of @xmath78 into the tree level higgs couplings to fermions .    at tree level , the off - diagonal elements of the cp - even higgs mass matrix are @xmath101 @xcite . when @xmath32 is small and @xmath0 is large , @xmath102 can be quite small , of the same order as its one loop radiative corrections . then it is possible to tune the radiatively corrected @xmath103 to zero by a careful choice of the mssm parameters , thereby driving the mixing angle @xmath78 to zero . if @xmath104 , the @xmath55 and @xmath77 couplings both vanish at tree level . however , the susy - qcd yukawa corrections to the @xmath55 coupling are nonzero , because they depend on the @xmath41 couplings to bottom squarks which remain finite at @xmath104 . thus at @xmath104 , the @xmath77 coupling vanishes while the @xmath55 coupling is nonzero due to the susy - qcd yukawa corrections . if we then vary the supersymmetric parameters , we can tune @xmath78 so that the tree level value of the @xmath55 coupling cancels its susy - qcd yukawa corrections . then the corrected @xmath55 coupling vanishes while the @xmath77 coupling is again nonzero . thus the @xmath55 and @xmath77 couplings vanish at different values of @xmath78 , or equivalently , at different points in susy parameter space . this behavior was first pointed out in ref . @xcite . of course , an on - shell diagrammatic calculation is needed to take into account terms of order @xmath85 from the external momenta . in ref . @xcite a partial on - shell diagrammatic calculation was performed , which includes an on - shell calculation of the corrections to @xmath78 and the on - shell susy - qcd corrections to @xmath71 , but does not include the @xmath105 susy - electroweak yukawa corrections to @xmath71 . a full one - loop diagrammatic calculation of the susy - electroweak corrections to @xmath71 was performed in ref . @xcite , although compact explicit expressions are not available . a similar calculation is in progress @xcite . the @xmath0 enhanced susy yukawa corrections modify the @xmath72 coupling through , e.g. , the first diagram of fig . [ fig : mssmdiags2 ] with @xmath107 ( @xmath108 ) replaced by @xmath109 ( @xmath110 ) and taking the charged higgs states in @xmath9 , @xmath111 . these corrections have important implications for the charged higgs boson search through @xmath112 at the tevatron @xcite because the reach in @xmath113 and @xmath0 depends on the effective @xmath114 and @xmath11 yukawa couplings . the one loop susy yukawa corrections to @xmath112 can be very large , of order the tree level amplitude , so that reliable calculations require a resummation or improvement . using the eft approach , we have at large @xmath0 @xcite @xmath115 with @xmath57 as in eq . [ eq : deltab ] . as described in sec . [ sec : intro ] , in this result @xmath57 gets no @xmath0 enhanced corrections at higher orders of the form @xmath116 @xcite . the remaining higher order corrections to @xmath57 are not @xmath0 enhanced . the susy yukawa corrections to the @xmath72 coupling have also been computed diagrammatically in refs . @xcite ( susy - qcd ) and @xcite ( susy - electroweak ) , giving results of the form @xmath117 this is equivalent to eq . [ eq : h+tbresum ] at one loop level , but in eq . [ eq : h+tbnoresum ] @xmath57 receives @xmath0 enhanced radiative corrections at higher orders . in ref . @xcite the tree - level input parameters were carefully chosen to keep the one - loop corrections in eq . [ eq : h+tbnoresum ] small . this is analogous to using running quark masses to absorb qcd corrections ; however it does not take into account the higher order @xmath0 enhanced susy corrections . the @xmath0 enhanced susy yukawa corrections lead to flavor changing neutral higgs interactions in the eft . this was first pointed out in ref . @xcite for @xmath1-@xmath118 mixing and expanded upon in ref . @xcite for leptonic @xmath1 meson decays . similar results have been found in diagrammatic calculations for a number of processes ; these will be discussed in sec .  [ sec : fcncproc ] . in this section we describe how flavor changing neutral higgs interactions arise in the eft .    as shown in sec . [ sec : intro ] , for @xmath119 the low energy effective theory of the mssm is the type iii 2hdm . in the type iii 2hdm , there is no natural flavor conservation and flavor changing neutral higgs couplings arise in general @xcite . in three generation notation , eq . [ eq : leffvevbasis ] becomes @xmath120 where we again use the vev basis , eq . [ eq : vevbasis ] . here @xmath121 are fermion generation indices and @xmath122 are general yukawa matrices , not necessarily diagonal . the down - type quark mass matrix is obtained by replacing the higgs fields with their vevs : @xmath123 note that @xmath124 does not appear in eq . [ eq:3genmass ] because @xmath38 has zero vev . diagonalizing the mass matrix in eq . [ eq:3genmass ] diagonalizes the yukawa matrix @xmath125 , which parameterizes the down - type fermion couplings to @xmath37 . the yukawa matrix @xmath126 , which parameterizes the down - type fermion couplings to @xmath38 , is not in general diagonal in the fermion mass basis . rewriting eq . [ eq:3genyuks ] in the fermion mass basis , we have @xmath127 clearly , the couplings of @xmath37 to down - type fermions are flavor diagonal , while those of @xmath38 are not . the off - diagonal elements in @xmath126 give flavor changing couplings of the states in @xmath128 ( @xmath40 and @xmath44 ) to down - type fermions . note that the flavor changing effects of the susy yukawa corrections in physical processes should decouple at large @xmath32 , for which @xmath129 and @xmath130 . there are two potential sources of flavor changing neutral higgs couplings in the mssm : minimal and non - minimal flavor violation . in the mssm with minimal flavor violation , the sfermion mass matrices are flavor - diagonal in the same basis as the quark and lepton mass matrices . then the only source of flavor changing is the ckm matrix , as in the sm . in this case the flavor changing neutral higgs couplings arise from one loop diagrams that contain a generation - changing @xmath131 , @xmath49 , or chargino coupling and an associated ckm matrix element . non - minimal flavor violation occurs when the sfermion mass matrices are not flavor - diagonal in the same basis as the quark and lepton mass matrices . when the sfermion mass matrices are diagonalized , flavor changing gluino - squark - quark and neutralino - sfermion - fermion couplings arise . non - minimal flavor violation is present in the most general mssm , and can lead to large flavor - changing effects in contradiction to experiment in , e.g. , @xmath132-@xmath133 mixing . this is the susy flavor problem , which must be solved in any realistic mssm scenario . attempts to solve the susy flavor problem include flavor - blind susy breaking scenarios ( e.g. , minimal supergravity ) , in which the sfermion mass matrices are flavor diagonal in the same basis as the quark and lepton mass matrices at the susy - breaking scale . however , a small amount of non - minimal flavor violation is typically regenerated as the sfermion and fermion mass matrices are run down to the electroweak scale . if non - minimal flavor violation is present in the mssm , then the flavor changing neutral higgs couplings receive contributions from one loop diagrams that contain a flavor - changing gluino or neutralino coupling , in addition to the contributions present in the minimal flavor violation scenario . the susy contributions to @xmath134 are well known @xcite . in particular , the chargino - top squark contribution to the amplitude is proportional to @xmath0 . it is possible to obey the experimental constraint on @xmath134 and still have large flavor changing effects in other processes from the chargino - top squark loop by choosing heavy enough chargino and top squark masses @xcite .    recently in ref . @xcite the higher order @xmath0 enhanced contributions to @xmath134 were resummed , following the formalism of ref . these higher order contributions can be large and can modify the regions of mssm parameter space excluded by @xmath134 @xcite . because the sm amplitude for @xmath136 is helicity suppressed , contributions from neutral higgs boson exchange in the 2hdm or mssm can compete with the sm amplitude at large @xmath0 . in the mssm with large @xmath0 , the dominant contribution to the amplitude comes from @xmath41 , @xmath42 and @xmath40 exchange with a flavor changing susy bubble in the external @xmath137 quark line , and grows with @xmath138 @xcite . in the mssm with minimal flavor violation the flavor changing susy bubble is a chargino - top squark loop ; if non - minimal flavor violation is present , additional contributions come from a gluino - bottom squark and neutralino - bottom squark loop . all other one - loop susy contributions have at most a @xmath139 enhancement . in the type ii 2hdm with large @xmath0 , penguin and box diagrams give a contribution to the amplitude that grows with @xmath139 and is of the same order as the sm contribution @xcite .    in the mssm , @xmath135 can be enhanced by three orders of magnitude over the sm rate because of the @xmath138 enhancement in the amplitude . this has been demonstrated in an eft calculation in ref . @xcite and in diagrammatic calculations in refs . the experimental sensitivity is best in the channel @xmath140 ; here the sm predicts @xmath141 @xcite , while the current experimental bound is @xmath142 ( 95% cl ) @xcite . at large @xmath0 and low @xmath32 , there are regions of susy parameter space in which @xmath143 can exceed its current upper bound @xcite ; thus susy parameter space is already being probed by this decay . future experiments at the tevatron run ii should improve the experimental bound by a factor of 40 with 2 fb@xmath144 of data @xcite , and further at an extended run ii . at the lhc this decay is expected to be observed at the sm rate after three years of running at low luminosity @xcite . @xmath1-@xmath118 mixing has been analyzed in the context of the effective type iii 2hdm in refs . @xcite . in the eft , a tree - level neutral higgs boson exchange diagram with flavor changing couplings at each vertex contributes to @xmath1-@xmath118 mixing . if the tree - level relations for mssm higgs boson masses and couplings are used , then the three tree - level eft diagrams involving @xmath41 , @xmath42 and @xmath40 exchange sum to zero @xcite . however , the tree - level relations for the mssm higgs boson masses and couplings are in general a poor approximation , and when radiative corrections to these masses and couplings are included the neutral higgs mediated contributions to @xmath1-@xmath118 mixing no longer cancel . in the sm , the radiative corrections to the ckm matrix are very small electroweak effects . in the mssm , however , there are @xmath0 enhanced flavor changing loop diagrams that may yield significant corrections to the ckm matrix . in ref . @xcite the down - type quark mass matrix was run down from a high scale and the @xmath0 enhanced susy corrections were included at the scale where the susy particles were integrated out ; diagonalizing the quark mass matrices then yielded the radiatively corrected ckm matrix . here we describe the source of the susy corrections to the ckm matrix in the eft .    when we diagonalized the down - type quark mass matrix in eq . [ eq:3genmass ] , the one loop susy corrections were implicitly included . writing the one loop corrections explicitly , we have @xmath145 in the vev basis this becomes , @xmath146 comparing this to eq . [ eq:3genyuks ] , @xmath125 is given by @xmath147 diagonalizing the down - type quark mass matrix diagonalizes @xmath125 . since @xmath148 are not in general diagonal in the same basis as the tree - level yukawa matrix @xmath149 , they yield an additional rotation of the mass matrix . this additional rotation is a correction to the ckm matrix .    at present , the ckm elements are not predicted by theory and must be input from experiment . if the ckm elements are measured solely through @xmath150 couplings to quarks , the susy corrections can simply be absorbed into the bare elements and are undetectable . however , if the ckm elements derived from @xmath150-quark - quark , @xmath49-quark - quark , and especially chargino - squark - quark couplings can be compared , the susy corrections may become apparent . we expect the chargino - squark - quark couplings to receive large corrections relative to the @xmath150-quark - quark couplings because susy - breaking effects will lead to different results for the flavor changing susy bubble diagrams in the external down - type quark and down - type squark lines . the susy radiative corrections that lead to flavor changing neutral higgs couplings are enhanced by @xmath0 and can be quite large , as we have seen . as in the flavor conserving case , these @xmath0 enhanced corrections should be resummed . such a resummation has been performed recently in ref . @xcite for higher - order corrections to @xmath134 , following the results in ref . @xcite . however , it is unclear whether this procedure will work in general because it is unclear whether the proof in ref . @xcite that all higher order @xmath0 enhanced terms are automatically resummed if the relation in eq . [ eq : ybmb ] is used is applicable to the flavor changing case . for example , factors of @xmath151 or @xmath152 can in principle arise at higher orders . this issue should be clarified before the resummation procedure is applied to additional flavor changing processes . it is clear that the @xmath0 enhanced susy corrections to the relation between down - type fermion masses and their yukawa couplings has the potential to be a good handle on the mssm at large @xmath0 . these corrections lead to large effects in both higgs physics and @xmath1 physics . because these effects can be quite large , reliable calculations are needed . in higgs boson decays , the external momenta are on the order of the electroweak scale and their effects should be included through diagrammatic calculations ; these are available for the susy - qcd corrections to @xmath71 and calculations are in progress for the susy - electroweak corrections to both @xmath71 and @xmath153 . in addition , resummation of higher order @xmath0 enhanced contributions beyond the one loop level is very important in some regions of parameter space . this resummation is well known and straightforward in the eft approach but should also be incorporated into the diagrammatic calculations . in flavor changing processes such as rare @xmath1 meson decays and ckm matrix renormalization , it is not entirely clear how the resummation should be done . finally , the susy corrections to the ckm matrix may have a significant effect on the @xmath49 and chargino couplings to ( s)fermions relative to the @xmath131 couplings . in short , the @xmath0 enhanced susy corrections to the relation between down - type fermion masses and their yukawa couplings offer a wide range of challenges and opportunities for mssm phenomenology . i am grateful to the members of the university of minnesota theoretical physics institute for organizing an excellent symposium and workshop where this work was presented , and to the other workshop participants for many lively discussions . i also thank u.  nierste and t.  plehn for fruitful discussions . fermilab is operated by universities research association inc .   under contract de - ac02 - 76ch03000 with the u.s . department of energy . h.  e.  haber , g.  l.  kane , phys . * 117 * , 75 ( 1985 ) . l.  j.  hall , r.  rattazzi , u.  sarid , phys . * d50 * , 7048 ( 1994 ) ; r.  hempfling , phys . rev .  * d49 * , 6168 ( 1994 ) ; m.  carena , m.  olechowski , s.  pokorski , c.  e.  m.  wagner , nucl . * b426 * , 269 ( 1994 ) . j.  f.  gunion , h.  e.  haber , nucl . * b272 * , 1 ( 1986 ) ; * b278 * , 449 ( 1986 ) [ e : * b402 * , 567 ( 1993 ) ] ; j.  f.  gunion , h.  e.  haber , g.  kane , s.  dawson , _ the higgs hunter s guide _ ( addison - wesley , reading , ma , 1990 ) [ e : hep - ph/9302272 ] . s.  l.  glashow , s.  weinberg , phys .  rev . * d15 * , 1958 ( 1977 ) ; e.  a.  paschos , phys . * d15 * , 1966 ( 1977 ) . d.  atwood , l.  reina , a.  soni , phys . rev .  * d55 * , 3156 ( 1997 ) . m.  carena , s.  mrenna , c.  e.  m.  wagner , phys . rev .  * d60 * , 075010 ( 1999 ) . f.  borzumati , g.  r.  farrar , n.  polonsky , s.  thomas , nucl . b555 * , 53 ( 1999 ) . m.  carena , h.  e.  haber , s.  heinemeyer , w.  hollik , c.  e.  m.  wagner , g.  weiglein , nucl . * b580 * , 29 ( 2000 ) . t.  appelquist , j.  carazzone , phys . rev .  * d11 * , 2856 ( 1975 ) . h.  e.  haber , y.  nir , nucl . phys .  * b335 * , 363 ( 1990 ) ; h.  e.  haber , in the proceedings of the workshop on electroweak symmetry breaking , budapest , hungary , july 11 - 13 , 1994 , p. 1 - 16 [ hep - ph/9501320 ] . d.  m.  pierce , j.  a.  bagger , k.  matchev , r.  j.  zhang , nucl . * b491 * , 3 ( 1997 ) . g.  d.  kribs , phys . rev .  * d62 * , 015008 ( 2000 ) . l.  randall , r.  sundrum , nucl . phys .  * b557 * , 79 ( 1999 ) ; g.  f.  giudice , m.  a.  luty , h.  murayama , r.  rattazzi , jhep * 9812 * , 027 ( 1998 ) . m.  carena , d.  garcia , u.  nierste , c.  e.  m.  wagner , nucl . b577 * , 88 ( 2000 ) . m.  carena , s.  mrenna , c.  e.  m.  wagner , phys . rev .  * d62 * , 055008 ( 2000 ) . h.  e.  logan , hep - ph/0012202 ; m.  carena , h.  e.  haber , h.  e.  logan , s.  mrenna , fermilab - pub-00/334-t , in preparation . k.  s.  babu , c.  kolda , phys . lett .  * b451 * , 77 ( 1999 ) . h.  e.  haber , m.  j.  herrero , h.  e.  logan , s.  pearanda , s.  rigolin , d.  temes , phys . * d63 * , 055004 ( 2001 ) . a.  dabelstein , nucl . phys .  * b456 * , 25 ( 1995 ) . j.  a.  coarasa , r.  a.  jimnez , j.  sol , phys . b389 * , 312 ( 1996 ) . g.  l.  kane , g.  d.  kribs , s.  p.  martin , j.  d.  wells , phys . * d53 * , 213 ( 1996 ) ; w.  loinaz , j.  d.  wells , phys . * b445 * , 178 ( 1998 ) ; h.  baer , j.  d.  wells , phys . rev .  * d57 * , 4446 ( 1998 ) . s.  heinemeyer , w.  hollik , g.  weiglein , eur . j.  * c16 * , 139 ( 2000 ) . h.  e.  haber , m.  j.  herrero , h.  e.  logan , s.  pearanda , d.  temes , in preparation . f.  abe et al . 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-6.5 cm fermilab - conf-01/010-t 0.25 cm hep - ph/0102029 5.7 cm in the minimal supersymmetric extension of the standard model ( mssm ) , fermion masses and yukawa couplings receive radiative corrections at one loop from diagrams involving the supersymmetric particles . 
 the corrections to the relation between down - type fermion masses and yukawa couplings are enhanced by @xmath0 , which makes them potentially very significant at large @xmath0 . 
 these corrections affect a wide range of processes in the mssm , including neutral and charged higgs phenomenology , rare @xmath1 meson decays , and renormalization of the ckm matrix . we give a pedagogical review of the sources and phenomenological effects of these corrections .