15627100
Phenomenology of spinless adjoints in two Universal Extra Dimensions
Abstract We discuss the phenomenology of ( 1 , 1 ) -mode adjoint scalars in the framework of two Universal Extra Dimensions. The Kaluza–Klein (KK) towers of these adjoint scalars arise in the 4-dimensional effective theory from the 6th component of the gauge fields after compactification. Adjoint scalars can have KK-number conserving as well as KK-number violating interactions. We calculate the KK-number violating operators involving these scalars and two Standard Model fields. Decay widths of these scalars into different channels have been estimated. We have also briefly discussed pair-production and single production of such scalars at the Large Hadron Collider.
15877
Invisible Higgs in theories of large extra dimensions
We discuss the possibility of detecting a Higgs boson in future collider experiments if large extra dimensions are realized in nature. In such a case, the Higgs boson can decay invisibly by oscillating into a graviscalar Kaluza-Klein (KK) tower. We show that the search for such a Higgs at an ee linear collider entails more complications than are usually thought of in relation to an invisibly decaying Higgs, the main sources of such complications being the simultaneous presence of a continuum graviton production and the broadening of the Higgs peak. We discuss possible ways of overcoming such difficulties, and conclude that the detection of such a Higgs boson might still be a problem beyond the mass range of 250-300 GeV.
54016829
Deciphering universal extra dimension from the top quark signals at the CERN LHC
Models based on Universal Extra Dimensions predict Kaluza-Klein (KK) excitations of all Standard Model (SM) particles. We examine the pair production of KK excitations of top- and bottom-quarks at the Large Hadron Collider. Once produced, the KK top/bottom quarks can decay to b-quarks, leptons and the lightest KK-particle, γ1, resulting in 2 b-jets, two opposite sign leptons and missing transverse momentum, thereby mimicing top-pair production. We show that, with a proper choice of kinematic cuts, an integrated luminosity of 100 fb−1 would allow a discovery for an inverse radius upto R−1 = 750GeV.
14197025
More on Violation of Angular-Momentum Selection Rules in Quantum Gravity
In a recent paper, we noticed that, in the s-channel scattering mediated by a graviton in the linearized Einstein theory, angular momentum seems not to be conserved in the graviton coupling to massive matter fields, due to the presence of a scalar component in the partial-wave expansion of the relevant amplitudes. The present Letter answers to some criticism by Han and Willenbrock, claiming that there is no problem in propagating a scalar component through a graviton exchange. We show explicitly that the partial-wave decomposition of the scattering amplitude contrasts with the rotation-group representations propagating through the graviton exchange in the considered processes. This phenomenon is crucially connected to the critical dependence of the trace of the graviton propagator on the effective dimension of the problem. In a recent work [1], we showed that angular-momentum selection rules are violated in the linearized limit of quantum gravity in the Einstein theory. In particular, we considered the scattering amplitudes of either massive fermion or massive gauge-boson pairs mediated by a graviton in the s-channel, and computed their non vanishing interferences with the amplitudes where a scalar field replaces the graviton. Since in the s-channel scattering of real particles only graviton components of angular momentum J = 2 propagate [2], a non vanishing interference with the scalar (J = 0) exchange 1 amplitude seems to point to a violation of the angular-momentum conservation in the graviton-matter vertex. Our statement was not based on special assumptions. It was derived in a straightforward way from the Feynman rules of the Einstein theory minimally coupled to massive fermion and vector-boson fields. In a following paper by Han and Willenbrock [3], it has been argued that our conclusion would be incorrect, since it is based on the wrong assumption that no J = 0 component is exchanged in the graviton propagator. The authors stress that in the s-channel amplitude mediated by a graviton, also an SO(3, 1) scalar component can propagate. The latter couples to the trace of the energy momentum tensor of the matter fields Tμν (that is non vanishing for massive fields). They conclude that there is no violation of angular-momentum selection rules in quantum gravity. In our paper [1], the crucial statement that only J = 2 graviton components contribute to the considered amplitudes was based on a previous work by van Dam and Veltman [2], and was not proved explicitly. The purpose of the present Letter is to clarify this issue, by showing that there are processes where there is a J = 0 component in the partial-wave decomposition of the s-channel amplitude, and, on the other hand, no J = 0 component propagates in the virtual graviton state. This fact will be shown to be crucially connected to the critical dependence of the trace of the graviton propagator tensor on the effective dimension of the analyzed problem. Let us consider the general form of the graviton propagator in the linearized Einstein theory. When contracted with conserved energy momentum tensors (i.e., for qμTμν = 0, with qμ the momentum flowing in the propagator), terms proportional to the momentum are not relevant, and the effective massless graviton propagator becomes∗ Gμναβ(q) = i Pμναβ q2 + iǫ ; Pμναβ = 1 2 (ημαηνβ + ημβηνα − ημνηαβ) , (1) The s-channel p1p1 → p2p2 scattering amplitude mediated by a graviton is then given by A = −i M P ( T f† μν Gμναβ(q) T i αβ ) (2) where T i(f) μν are the matrix elements of the conserved energy momentum tensor of the initial (final) states, and MP is the Planck mass. In this Letter, indices (μ, ν, α, β) are contracted according to the Minkowski metric ημν = Diag(1,−1,−1,−1).
119099061
Probing the violation of equivalence principle at a muon storage ring via neutrino oscillation
Abstract We examine the possible tests of violation of the gravitational equivalence principle (VEP) at a muon storage ring via neutrino oscillation experiments. If the gravitational interactions of the neutrinos are not diagonal in the flavour basis and the gravitational interaction eigenstates have different couplings to the gravitational field, this leads to the neutrino oscillation. If one starts with μ + beam then appearance of τ ± , e + and μ − in the final state are the signals for neutrino oscillation. We have estimated the number of μ − events in this scenario in ν μ – N deep inelastic scattering. Final state lepton energy distribution can be used to distinguish the VEP scenario from the others. A large area of VEP parameter space can be explored at a future muon storage ring facility with moderate beam energy.
657627
Virtual graviton exchanges at the Z pole in large extra dimensions
Abstract In the framework of quantum gravity propagating in large extra dimensions, the effects of virtual Kaluza–Klein gravitons on the imaginary part of the amplitude of the process e + e − →f f are analyzed at the Z pole. Notably, the interference of the almost-continuous spectrum of the KK gravitons with the standard model resonant amplitude is finite and predictable in terms of the fundamental D-dimensional Planck scale MD. We find that, while the virtual-graviton effect on total cross sections vanishes at tree-level, both angular and polarization asymmetries are modified by terms whose relative effect is at most of order 10−4 for MD>1 TeV. Possible shifts in MZ, due to the changes in Breit–Wigner line shape are also discussed.
118071488
Single Top Production and Extra Dimensions
In extra dimension theories, where the gauge bosons of the standard model propagate in the bulk of the extra dimensions, there are Kaluza‐Klein excitations of the standard model gauge bosons that can couple to the standard model fermions. In this paper we study the effects of the excited Kaluza‐Klein modes of the W on single top production at the Tevatron.
2536708
Flavor changing processes in quarkonium decays
We study the flavor changing processes Y-->B/(B) over bar X-s and J/psi-->D/(D) over bar X-u in B factories and tau-charm factories. In the standard model, these processes are predicted to be unobservable; so they serve as a probe of new physics. We first perform a model-independent analysis, then examine the predictions of the models, such as the top-color models, the MSSM with R-parity violation, and the two-Higgs-doublet model, for the branching ratios of Y-->B/(B) over bar X-s and J/psi-->D/(D) over bar X-u. We find that these branching ratios could be as large as 10(-6) and 10(-5) in the presence of new physics. [S0556-2821(99)00513-5].
118720377
Explaining the $B \to K^\ast \mu^+ \mu^-$ data with scalar interactions
Recent LHCb results on the decay $B \to K^\ast \mu^+ \mu^-$ show significant deviations from the SM estimates in some of the angular correlations. In this paper we study the possibility of explaining these deviations using new scalar interactions. We show that new dimension-6 four-quark operators of scalar and pseudo-scalar type can successfully account for the discrepancies even after being consistent with other experimental measurements. We also briefly discuss possible extensions of the Standard Model where these operators can be generated.
119399562
Nonuniversal correction to Z ---> b anti-b and single top quark production at Tevatron
New physics associated with the heavy top quark can affect top quark production and the partial decay width of $Z \rightarrow b \bar b$. In this paper, we examine the correlated effects of possible new physics on ${R_b}$ measured at LEP I and the single top quark production rate at Tevatron by using an effective lagrangian technique. We point out that certain operators in the effective lagrangian, constrained by the measured value of $R_b$, can lead to significant and potentially observable effects in single top production.
14242173
Vacuum stability in Split SUSY and Little Higgs models
We study the stability of the effective Higgs potential in the split supersymmetry and Little Higgs models. In particular, we study the effects of higher dimensional operators in the effective potential on the Higgs mass predictions. We find that the size and sign of the higher dimensional operators can significantly change the Higgs mass required to maintain vacuum stability in Split SUSY models. In the Little Higgs models the effects of higher dimensional operators can be large because of a relatively lower cutoff scale. Working with a specific model we find that a contribution from the higher dimensional operator with coefficient of O(1) can destabilize the vacuum.