Browsing by Author "Faisel, Gaber"

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Axigluon on like-sign charge asymmetry A(sl)(b), FCNCs and CP asymmetries in B decays
(ELSEVIER, 2011) Chen, Chuan-Hung; Faisel, Gaber
A non-universal axigluon in generalized chiral color models leads to flavor changing neutral currents (FCNCs) at tree level. We analyze phenomenologically the new contributions to B-q (q = d, s) mixing and the related CP asymmetries (CPAs) that are generated by axigluon exchange. We find that although Delta mB(q), can give a strict constraint on the parameters of b -> q transition, the precise measurement of sin 2 beta(0)(J/psi K) can further exclude the parameter space of d transition. The axigluon-mediated effects can enhance the like-sign dimuon charge asymmetry A(sl)(b) by one order of magnitude larger than the standard model prediction. Accordingly, large CPA sin 2 beta(J/psi phi)(s) and CPA difference sin 2 beta(0)(J Psi k) sin 2 beta(0)(phi k) are achieved. (C) 2011 Elsevier B.V. All rights reserved.
Charged Higgs contribution to (B)over-bar(s) -> phi pi(0) and (B)over-bar(s) -> phi rho(0)
(ELSEVIER SCIENCE, 2014) Faisel, Gaber
We study the decay modes (B) over bar (s) -> phi pi(0) and (B) over bar (s) -> phi rho(0) within the frameworks of two-Higgs doublet models type-II and type-III. We adopt in our study Soft Collinear Effective Theory as a framework for the calculation of the amplitudes. We derive the contributions of the charged Higgs mediation to the weak effective Hamiltonian governing the decay processes in both models. Moreover, we analyze the effect of the charged Higgs mediation on the Wilson coefficients of the electroweak penguins and on the branching ratios of (B) over bar (s) -> phi pi(0) and (B) over bar (s) -> phi rho(0) decays. We show that within two-Higgs doublet models type-II and type-III the Wilson coefficients corresponding to the electroweak penguins can be enhanced due to the contributions from the charged Higgs mediation leading into enhancement in the branching ratios of (B) over bar (s) -> phi pi(0) and (B) over bar (s) -> phi rho(0) decays. We find that, within two-Higgs doublet models type-II, the enhancement in the branching ratio of (B) over bar (s) -> phi pi(0) cannot exceed 18% with respect to the SM predictions. For the branching ratio of (B) over bar (s) -> phi rho(0), we find that the charged Higgs contribution in this case is small where the branching ratio of (B) over bar (s) -> phi rho(0) can be enhanced or reduced by about 4% with respect to the SM predictions. For the case of the two-Higgs doublet models type-III we show that the branching ratio of (B) over bar (s) -> phi pi(0) can be enhanced by about a factor 2 of its value within two-Higgs doublet models type-II. However, no sizeable enhancement with respect to the SM predictions can be obtained for both (B) over bar (s) -> phi pi(0) and (B) over bar (s) -> phi rho(0) decays. (C) 2014 The Author. Published by Elsevier B.V.
Constraining nonstandard neutrino-electron interactions due to a new light spin-1 boson
(SPRINGER, 2013) Chiang, Cheng-Wei; Faisel, Gaber; Lin, Yi-Fan; Tandean, Jusak
We consider nonstandard interactions of neutrinos with electrons arising from a new light spin-1 particle with mass of tens of GeV or lower and couplings to the neutrinos and electron. This boson is not necessarily a gauge boson and is assumed to have no mixing with standard-model gauge bosons. Adopting a model-independent approach, we study constraints on the flavor-conserving and -violating couplings of the boson with the leptons from a number of experimental data. Specifically, we take into account the (anti)neutrino-electron scattering and e(+)e(-) -> nu(nu) over bar gamma measurements and keep explicitly the dependence on the new particle mass in all calculations. We find that one of the two sets of data can provide the stronger constraints, depending on the mass and width of the boson. Also, we evaluate complementary constraints on its separate flavor-conserving couplings to the electron and neutrinos from other latest experimental results.
Effects of two inert scalar doublets on Higgs boson interactions and the electroweak phase transition
(AMER PHYSICAL SOC, 2015) Ahriche, Amine; Faisel, Gaber; Ho, Shu-Yu; Nasri, Salah; Tandean, Jusak
We study some implications of the presence of two new scalar weak doublets beyond the standard model which have zero vacuum expectation values and are charged under an extra Abelian gauge symmetry. The additional gauge sector does not couple directly to standard-model particles. We investigate specifically the effects of the scalars on oblique electroweak parameters and on the interactions of the 125 GeV Higgs boson, especially its decay modes h --> gamma gamma, gamma Z and trilinear self-coupling, all of which will be probed with improved precision in future Higgs measurements. Moreover, we explore how the new scalars may give rise to strongly first-order electroweak phase transition and also show its correlation with sizable modifications to the Higgs trilinear self-coupling.
Exploring high-mass diphoton resonance without new colored states
(ELSEVIER SCIENCE BV, 2017) Ahriche, Amine; Faisel, Gaber; Nasri, Salah; Tandean, Jusak
A new heavy resonance may be observable at the LHC if it has a significant decay branching fraction into a pair of photons. We entertain this possibility by looking at the modest excess in the diphoton invariant mass spectrum around 750 GeV recently reported in the ATLAS and CMS experiments. Assuming that it is a spinless boson, dubbed (s) over tilde, we consider it within a model containing two weak scalar doublets having zero vacuum expectation values and a scalar singlet in addition to the doublet responsible for breaking the electroweak symmetry. The model also possesses three Dirac neutral singlet fermions, the lightest one of which can play the role of dark matter and which participate with the new doublet scalars in generating light neutrino masses radiatively. We show that the model is consistent with all phenomenological constraints and can yield a production cross section sigma (pp -> (s) over tilde -> gamma gamma) of roughly the desired size, mainly via the photon-fusion contribution, without involving extra colored fermions or bosons. We also discuss other major decay modes of (s) over tilde which are potentially testable in upcoming LHC measurements. (C) 2017 The Author(s). Published by Elsevier B.V.
Exploring X-ray lines as scotogenic signals
(ELSEVIER, 2014) Faisel, Gaber; Ho, Shu-Yu; Tandean, Jusak
We consider some implications of X-ray lines from certain astronomical objects as potential effects of dark matter decay in the context of the scotogenic model, where neutrinos acquire mass radiatively via one-loop interactions with dark matter. As an example, we focus on the 3.5 keV line recently detected in the X-ray spectra of galaxy clusters, assuming that it stands future scrutiny. We explore the scenario in which the line originates from the slow decay of fermionic dark matter in the model. After obtaining anumber of benchmark points representing the parameter space consistent with the new data and various other constraints, we make predictions on several observables in leptonic processes. They include the effective Majorana mass in neutrinoless double-beta decay, the sum of neutrino masses, and the rate of flavor-changing decay mu -> e gamma, as well as the cross sections of e(+)e(-) collisions into final states containing nonstandard particles in the model. These are testable in ongoing or future experiments and thus offer means to probe the scotogenic scenario studied. (C) 2014 The Authors. Published by Elsevier B. V. This is an open access article under the CC BY license (http://creativecommons. org/licenses/by/3.0/). Funded by SCOAP(3).
Majorana versus Dirac mass from holomorphic supersymmetric Nambu-Jona-Lasinio model
(AMER PHYSICAL SOC, 2013) Dai, Yan-Min; Faisel, Gaber; Jung, v
dy the theoretical features in relation to dynamical mass generation and symmetry breaking for the recently proposed holomorphic supersymmetric Nambu-Jona-Lasinio model. The basic model has two different chiral superfields (multiplets) with a strongly coupled dimension five four-superfield interaction. In addition to the possibility of generation of Dirac mass between the pair established earlier, we show here the new option of generation of Majorana masses for each chiral superfield. We also give a first look at what condition may prefer Dirac over Majorana mass, illustrating that a split in the soft supersymmetry breaking masses is crucial. In particular, in the limit where one of the soft masses vanish, we show that generation of the Majorana mass is no longer an option, while the Dirac mass generation survives well. The latter is sensitive mostly to the average of the two soft masses. The result has positive implication on the application of the model framework towards dynamical electroweak symmetry breaking with Higgs superfields as composites. DOI: 10.1103/PhysRevD.87.085033
New physics effects in D+ -> K- pi(+) pi(+)
(IOP PUBLISHING LTD, 2015) Delepine, David; Faisel, Gaber; Ramirez, Carlos A.
In this paper, we study the Cabibbo favored three body non-leptonic D+ -> K-pi(+)pi(+) decay. We show that the corresponding direct charge parity (CP) asymmetry is extremely tiny in the framework of the Standard Model (SM) and is out of experimental range. Motivated by this result we extend the study of the CP asymmetries to include a generic model where the CPV weak phase equals 20 degrees in a(2), a model with extra gauge bosons within left-right (LR) grand unification models and a model with a charged Higgs boson. We show that the generic model can strongly enhance CP asymmetries-reaching up to 30% in some regions of the Dalitz plots and still being compatible with the existing experimental limit on the total CP asymmetry in this channel. Large CP asymmetries can be achieved in the non-manifest LR models where partial CP asymmetries up to a few % can be reached and the experimental limit on the total CP asymmetry already can be used to constraint these LR SM extensions. For the two Higgs doublets models the CP asymmetries are of order 10(-3).
Observation of CP violation in D-0 -> K-pi(+) as a smoking gun for new physics
(AMER PHYSICAL SOC., 2013) Delepine, David; Faisel, Gaber; Ramirez, Carlos A.
In this paper, we study the Cabibbo favored nonleptonic D-0 decays into K-pi(+) decays. First we show that, within the Standard Model (SM), the corresponding charge conjugation and parity (CP) asymmetry is strongly suppressed and out of the experimental range, even taking into account the large strong phases coming from final state interactions. We show also that although new physics models with extra sequential generation can enhance the CP asymmetry by a few orders of magnitude, the resulting CP asymmetry is still far from the experimental range. The most sensitive new physics models to this CP asymmetry come from nonmanifest left-right models, where a CP asymmetry up to 10% can be reached, and the general two-Higgs model extension of the SM, where a CP asymmetry of order 10(-2) can be obtained without being in contradiction with the experimental constraints on these models. DOI: 10.1103/PhysRevD.87.075017
Supersymmetric contributions to (B)over-bar(s) -> phi pi(0) and (B)over-bar(s) -> phi rho(0) decays in SCET
(SPRINGER, 2012) Faisel, Gaber
We study the decay modes (B) over bar (s) phi pi(0) and (B) over bar (s) phi rho(0) using Soft Collinear Effective Theory. Within Standard Model and including the error due to the SU(3) breaking effect in the SCET parameters we find that BR (B) over bar (s) phi pi(0) =7(-1-2)(+1+2) x 10(-8) and BR (B) over bar (s) -> phi pi(0) = 9(-1-4)(+1+3) corresponding to solution 1 and solution 2 of the SCET parameters respectively. For the decay mode (B) over bar (s) phi rho(0), we find that BR (B) over bar (s) phi rho(0) = 20.2(-1-12)(+1+9) x 10(-8) and BR (B) over bar (s) phi rho(0) = 34.0(-1.5-22)(+1.5+15) x 10(-8) corresponding to solution 1 and solution 2 of the SCET parameters respectively. We extend our study to include supersymmetric models with non- universal A- terms where the dominant contributions arise from diagrams mediated by gluino and chargino exchanges. We show that gluino contributions can not lead to an enhancement of the branching ratios of (B) over bar (s) -> phi pi(0) and (B) over bar (s) -> phi rho(0) In addition, we show that SUSY contributions mediated by chargino exchange can enhance the branching ratio of (B) over bar (s) -> phi pi(0) by about 14% with respect to the SM prediction. For the branching ratio of (B) over bar (s) -> phi rho(0), we find that SUSY contributions can enhance its value by about 1% with respect to the SM prediction.