arXiv subjects

Amarjit Soni

Publications and source records attributed to Amarjit Soni.

At least 181 records · Page 10Linked to original sources

arXiv2000

Gauge Boson - Gauge Boson Scattering in Theories with Large Extra Dimensions

We consider the scattering amplitudes of the form V_1 V_2 -> V_3 V_4, where V_i=γ, Z, W or g(=gluon) are the Standard Model gauge bosons, due to graviton exchange in Kaluza-Klein theories with large extra dimensions. This leads to a number of experimentally viable signatures at high energy leptonic and hadronic colliders. We discuss the observability or future limits on the scale of the gravitational interactions (m_D), that may be obtained at an e+e- Next Linear Collider (NLC) and at the LHC, by studying some of these type of gauge boson scattering processes. We find that the attainable limits through these type of processes are: m_D > 3 TeV at the NLC and m_D > 6 TeV at the LHC.

hep-ph↗

arXiv1999

Dijet Production at Hadron Colliders in Theories with Large Extra Dimensions

We consider the production of high invariant mass jet pairs at hadron colliders as a test for TeV scale gravitational effects. We find that this signal can probe effective Planck masses of about 10 TeV at the LHC with center of mass energy of 14 TeV and 1.5 TeV at the Tevatron with center of mass energy of 2 TeV. These results are compared to analogous scattering processes at leptonic colliders.

hep-ph↗

arXiv1999

Graviton Production By Two Photon and Electron-Photon Processes In Kaluza-Klein Theories With Large Extra Dimensions

We consider the production of gravitons via two photon and electron-photon fusion in Kaluza-Klein theories which allow TeV scale gravitational interactions. We show that at electron-positron colliders, the processes l+l- -> l+ l- graviton, with l=e, mu, can lead to a new signal of low energy gravity of the form l+l- -> l+l- + missing energy which is well above the Standard Model background. For example, with two extra dimensions at the Next Linear Collider with a center of mass energy of 500 or 1000 GeV, hundreds to thousands such l+ l- graviton events may be produced if the scale of the gravitational interactions, M_D, is around a few TeV. At a gamma-electron collider, more stringent bounds may be placed on M_D via the related reaction e^-γ-> e^- graviton. For instance, if a 1TeV electron positron collider is converted to an electron-photon collider, a bound of ~10TeV may be placed on the scale M_D if the number of extra dimensions delta=2 while a bound of ~4TeV may be placed if delta=4.

hep-ph↗

arXiv1999

General analysis of B decays to two pseudoscalars for EWP, rescattering and color suppression effects

A general analysis for B decays to two pseudoscalars, involving ten modes, is presented. A simple model for final state interactions and rescattering effects is proposed. We show how the data can be used to deduce important information on electroweak penguins (EWP), rescattering and color suppression effects and on the CKM parameters in a largely model independent way by using chisquared-minimization. We find that the current data suggests the presence of color-suppressed tree at levels somewhat larger than simple theoretical estimates. Once the data improves the extraction of alpha and/or gamma may become feasible with this method as we illustrate with the existing data.

hep-ph↗

arXiv1999

Graviton Production By Two Photon Processes In Kaluza-Klein Theories With Large Extra Dimensions

We consider the production of gravitons via two photon fusion in Kaluza-Klein theories which allow TeV scale gravitational interactions. We find that the processes l+ l- to l+ l- + graviton, with l=electron or muon can put quite stringent bounds on such theories. For example, with two extra dimensions at the Next Linear Collider with a center of mass energy of 500 (1000) GeV attainable bounds on the scale of the gravitational interactions can reach about 6 (9) TeV.

hep-ph↗

arXiv1999

CP Violation in B Decays in a 2-Higgs Doublet Model for the Top Quark

In the absence of natural flavor conservation, multi-Higgs doublet models generally contain new sources of CP violation and anomalous charged Higgs Yukawa couplings. We present a charged-Higgs CP violation study of one such two-Higgs doublet model (2HDM) which treats the top quark differently from the other quarks. The phenomenological implications for the K-Kbar system and for B decays differ significantly from those of the standard model (SM) and of the 2HDM's with natural flavor conservation. In particular, the SM phase in this model could take a wide range of values, and the CP asymmetry in the "gold-plated" decay mode B to J/psi K_S could be quite different from and even of opposite sign relative to the SM prediction. A new mechanism is also noted for generating a large neutron electric dipole moment which is close to the present experimental limit.

hep-ph↗

arXiv1999

CP Violation in a two-Higgs doublet model for the top quark: B to psi K_S

We explore charged-Higgs CP-violating effects in an intriguing two-Higgs doublet model which accords special status to the top quark. In this model the heaviness of the top quark originates naturally from the much larger VEV of the second Higgs doublet compared to that of the first. The phenomenology of this model is quite distinct from that of the usual formulations of the two-Higgs doublet model. In particular, the model can easily account for the observed CP violation in the kaon sector even if the CKM matrix is real. The associated non-standard CP phase can be monitored through measurements of the time-dependent CP asymmetry in B to psi K_S in experiments at the upcoming B-factories.

hep-ph↗

arXiv1998

Light quark masses using domain wall fermions

We compute the one-loop self-energy correction to the massive domain wall quark propagator. Combining this calculation with simulations at several gauge couplings, we estimate the strange quark mass in the continuum limit. The perturbative one-loop mass renormalization is comparable to that for Wilson quarks and considerably smaller than that for Kogut-Susskind quarks. Also, scaling violations appear mild in comparison to other errors at present. Given their good chiral behavior and these features, domain wall quarks are attractive for evaluating the light quark masses. Our preliminary quenched result is m_s(2 GeV) = 82(15) MeV in the ${\bar{MS}}$ scheme.

hep-lat↗

arXiv1998

Extracting information on CKM phases, electro-weak penguins and new physics from B --> VV decays

We derive constraints for $B\to VV$ modes ($V= vector meson) that allow aquantitative assessment of the contributions from electroweak penguins (EWP) and/or new physics. Interplay of direct CP with oscillation studies then leads to the extraction of the angles alpha and gamma, using B--> K* omega rho and B--> rho omega (phi) respectively, if by using our constraint equations it can be experimentally demonstrated that color-suppressed EWP are small.

hep-ph↗

arXiv1998

Two body decays of the $b$-quark: Applications to direct CP violation, searches for electro-weak penguins and new physics

A systematic experimental search for two-body hadronic decays of the b-quark of the type b to quark + meson is proposed. These reactions have a well defined experimental signature and they should be theoretically cleaner compared to exclusive decays. Many modes have appreciable branching ratios and partial rate asymmetries may also be quite large (about 8-50%) in several of them. In a few cases electroweak penguins appear to be dominant and may be measurable. CP violating triple correlation asymmetries provide a clean test of the Standard Model.

hep-ph↗

arXiv1997

The Possibility of Large Direct CP Violation in B to K pi-Like Modes Due to Long Distance Rescattering Effects and Implications for the Angle gamma

We consider the strong rescattering effects that can occur in the decays such as B -> K pi, K* pi, K rho... and their impact on direct CP violation in these modes. First we discuss, in general, how the CPT theorem constrains the resulting pattern of partial rate asymmetries leading to different brands of direct CP. Traditional discussions have centered around the absorptive part of the penguin graph which has Delta I=0 in b -> s transitions and as a result causes ``simple'' CP violation; long-distance final state rescattering effects, in general, will lead to a different pattern of CP: ``compound'' CP violation. Predictions of simple CP are quite distinct from that of compound CP. Final states rescattering phases in B decays are unlikely to be small possibly causing large compound CP violating partial rate asymmetries in these modes. CPT theorem requires a cancellation of PRA due to compound CP amongst the $Kπ$ states themselves; thus there can be no net cancellation with other states such as K*π, Kρetc. Therefore, each class of such modes, namely K pi, K rho, K^*pi, K a_1 etc. can have large direct CP emanating from rescattering effects. Various repercussions for the angle $γ$ are also discussed.

hep-ph↗

arXiv1997

Desperately Seeking Non-Standard Phases via Direct CP Violation in $b\to sg^\ast$ Process

Attributing the recent CLEO discovery of $B \to η' + X_s$ to originate (primarily) from the fragmentation of an off-shell gluon ($g^*$) via $b \to s + g^*$, $g^* \to g + η'$, we emphasize that many such states ($X_g$) should materialize. Indeed the hadronic fragments ($X_g$) of $g^*$ states are closely related to those seen in $ψ\to γ(ϕ, ω) + X_g$. A particular final state of considerable interest is $X_g=K^+K^-$. Signals from such states in $B$ decays can be combined to provide a very sensitive search for CP violating phase(s) from non-standard physics. The method should work even if the contribution of these source(s) to the rates is rather small ($\sim10%$) to the point that a comparison between theory and experiment may find it extremely difficult to reveal the presence of such a new physics.

hep-ph↗

arXiv1997

Improving constraints on tan(beta)/m_H using B \to D tau \bar{nu}

We study the q^2 dependence of the exclusive decay mode B \to D tau \bar{nu} in type II two Higgs doublet models and show that this mode may be used to put stringent bounds on tan(beta)/m_H. There are currently rather large theoretical uncertainties in the q^2 distribution, but these may be significantly reduced by future measurements of the analogous distribution for B \to D(e,mu)\bar{nu}. We estimate that this reduction in the theoretical uncertainties would eventually (i.e., with sufficient data) allow one to push the upper bound on tan(beta)/m_H down to about 0.06 GeV^{-1}. This would represent an improvement on the current bound by about a factor of 7. We then apply the method of optimized observables which allows us to estimate the reach of an experiment with a given number of events. We thus find that an experiment with, for example, 10^3 events could set a 2σupper bound on tan(beta)/m_H of 0.07 GeV^{-1} or could differentiate at the 4.6σlevel between a 2HDM with tan(beta)/m_H = 0.1 GeV^{-1} and the SM.

hep-ph↗

arXiv1997

QCD corrections to b -> s gamma gamma induced decays: B -> X_s gamma gamma and B_s -> gamma gamma

We present a complete calculation of the Leading Order QCD corrections to the quark level decay amplitude for b -> s gamma gamma and study their relevance for both the inclusive branching ratio BR(B -> X_s gamma gamma) and for the exclusive decay channel B_s -> gamma gamma. In addition to the uncertainties in the short distance calculation, due to the choice of the renormalization scale, an appreciable uncertainty in both B_s -> gamma gamma and B -> X_s gamma gamma is introduced by the matrix element calculation. We also briefly discuss some long distance effects, especially those due to the eta_c resonance for the inclusive rate. Finally, the analysis of the IR singularities of the two photon spectrum in the inclusive case is given.

hep-ph↗

arXiv1997

B to eta' + X and The QCD Anomaly

Mechanisms for the observed large $Br(B \to η' +X_s)$ are examined. We propose that the dominant fraction of the $B \to η' +X_s$ rate is due mainly to $b \to s g^*$, where $g^*$ is an off-shell gluon, followed by $g^* \to gη'$ via the anomalous coupling of the $η'$ to two gluons. The calculated rate for $B \to η'+X_s$ is in rough accord with experiment using a fairly constant glue-glue-$η'$ form factor. This behavior of the form factor may be indicative of glueball dominance of the channel. Searches via the modes $η' h^+h^-$ ($h=π$ or $K$) may be worthwhile. Charmonia contributions [i.e $B \to η_c, ψ(\to η'+X) +X_s$] can only account for at most 20% of the central value of the signal. Implications for $B \to η' +X_d$ and for the corresponding $η$ modes are also given.

hep-ph↗

arXiv1997

Measuring the CP Angle βin Hadronic b\to s Penguin Decays

Asymmetric e^+e^- colliders running on the Υ(4S) (B factories) will much more readily measure CP-violating asymmetries in the decays of B_d^0 and B^\pm mesons than in the decays of B_s^0 mesons. As such, they will seemingly not be able to probe new phases in Bs-Bs(bar) mixing, i.e. in b\to s transitions. However, by measuring the CP angle βvia b \to s hadronic penguin decays such as B_d^0 \to η'\ks and B_d^0 \toϕ\ks, and comparing its value to that obtained in B_d^0 \toΨ\ks, it is possible to detect the presence of new physics in the b\to s flavour-changing neutral current. Recent CLEO results are encouraging in this regard. They suggest that the branching ratio of the b\to s penguin decay B_d^0 \to η'\ks is anomalously large, about 4 \times 10^{-5}, which will make it much easier to search for new physics in b\to s transitions.

hep-ph↗

arXiv1997

Mixing-induced CP Asymmetries in Radiative B Decays in and beyond the Standard Model

In the Standard Model (SM) the photon in radiative $\bar B^0$ and $\bar B_s$ decays is predominantly left-handed. Thus, mixing induced CP asymmetries in $b\to sγ$ and $b\to dγ$ are suppressed by $m_s/m_b$ and $m_d/m_b$, respectively, and are very small. In many extensions of the SM, such as the left-right symmetric model (LRSM), SU(2)xU(1) models with exotic fermions and SUSY, the amplitude of right-handed photons grows proportional to the virtual heavy fermion mass, which can lead to large asymmetries. As an example, in the LRSM, asymmetries larger than 50% are possible even when radiative decay rate measurements agree with SM predictions.

hep-ph↗

arXiv1997

Parity Violation in Bottom Quark Pair Production at Polarized Hadron Colliders

Parity violation induced by the chromo-anapole form factor of the bottom quark, generated from weak corrections, is studied in polarized hadron collisions. The forward-backward asymmetry in the bottom quark pair production at polarized $pp$ and $p\bar{p}$ colliders is evaluated in the Standard Model and in a Two Higgs Doublet Model to examine the effects of parity violation. In the models studied, promising results are found for polarized $p\bar{p}$ colliders.

hep-ph↗