17475961
ZZH coupling: a probe to the origin of EWSB?
Abstract We argue that the ZZH coupling constitutes a simple probe of the nature of the scalar sector responsible for electroweak symmetry breaking. We demonstrate the efficacy of this measure through an analysis of four-dimensional models containing scalars in arbitrary representation of SU (2)× U (1), as well as extra-dimensional models with a non-factorizable geometry. A possible role for the t t H couplings is also discussed.
118117079
Mutual consistency of the MINOS and MiniBooNE Antineutrino Results and Possible CPT Violation
Discussing the recent MINOS data on muon anti-neutrino disappearance and the MiniBooNE data on muon anti-neutrino to electron anti-neutrino oscillation, we show that the while the respective best fits are inconsistent with each other, significant overlap of allowed regions does exist. Assuming only three neutrino species, the data indicates a discrepancy of mass levels and mixing angles between the neutrino and the antineutrino sectors. We show that the existing data can be reconciled with a model of explicit CPT violation in the neutrino sector and estimate the magnitude of the required violation.
118278744
Higgs Boson Signals in Three b-jet Final States at the Fermilab Tevatron
At the Fermilab Tevatron, final states with three tagged b-jets could play an important role in searches for a Higgs boson with mass in the range 100-300 GeV. These signals arise from gb fusion and we demonstrate their observability in the limit of a large b-quark Yukawa coupling. Rather promising discovery limits on such a coupling are obtained and consequent effects on the parameter space of the Higgs-boson sector in the MSSM are discussed.
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.
118845399
Vacuum stability constraints and LHC searches for a model with a universal extra dimension
If the new boson lying in the narrow mass range between 122 and 127 GeV is confirmed to be a Higgs boson, then stability of the electroweak vacuum in a minimal model with a universal extra dimension (mUED) will require a much lower cutoff for the theory than has been envisaged earlier. We show that this low cutoff leads to important changes in much of the minimal model with a universal extra dimension phenomenology studied till now. In particular, prospects for LHC searches for $n=1$ states are rather limited, while resonant $n=2$ states may go completely undetected. Prospects for detection at high energy ${e}^{+}{e}^{\ensuremath{-}}$ colliders are less affected.
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).
118592122
Probing light pseudoscalar, axial vector states through $\eta_{b} \to\tau^{+}\tau^{-}$
In this paper, we explore the decay ${\ensuremath{\eta}}_{b}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ as a probe for a light pseudoscalar or a light axial vector state. We estimate the standard model branching ratio for this decay to be $\ensuremath{\sim}4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$. We show that considerably larger branching ratios, up to the present experimental limit of $\ensuremath{\sim}8%$, are possible in models with a light pseudoscalar or a light axial vector state. As we do not include possible mixing effects between the light pseudoscalar and the ${\ensuremath{\eta}}_{b}$, our results should be reliable when the pseudoscalar mass is away from the ${\ensuremath{\eta}}_{b}$ mass.
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.
119363366
Flavor changing decays of Upsilon and J / psi
We study flavor changing processes $\Upsilon \to B/{\bar B} X_s$ and $J/\psi \to D/{\bar D} X_u$ in the B factories and the Tau-Charm factories. In the standard model, these processes are predicted to be unobservable, so they serve as a probe of the new physics. We first perform a model independent analysis, then examine the predictions of models; such as top color models and MSSM with R-parity violation ; for the branching ratios of $\Upsilon \to B/{\bar B} X_s$ and $J/\psi \to D/{\bar D} X_u$ . We find that these branching ratios could be as large as $10^{-6}$ and $10^{-5}$ in the presence of new physics.
204935588
Measuring beta in B ---> D(*)+ D(*)- K(s) decays
We consider the possibility of measuring both $\sin (2 \beta)$ and $\cos (2 \beta)$ in the KM unitarity triangle using the process $B^0 \to D^{*+}D^{*-}K_s$. This decay mode has a higher branching fraction (O(1%)) than the mode $B^0 \to D^{*+}D^{*-}$. We use the factorization assumption and heavy hadron chiral perturbation theory to estimate the branching fraction and polarization. The time dependent rate for $B^0(t) \to D^{*+} D^{*-} K_s$ can be used to measure $\sin (2 \beta)$ and $\cos(2 \beta)$ . Furthermore, examination of the $D^{*+} K_s$ mass spectrum may be the best way to experimentally find the broad $1^+$ p-wave $D_s$ meson.
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.