arXiv subjects

Gaber Faisel

Publications and source records attributed to Gaber Faisel.

At least 19 recordsLinked to original sources

arXiv2026

Flavor Violations in $B$-Mesons within Non-Minimal SU(5)

Recent anomalies in $B$-meson decays, such as deviations in $R_{D^{(*)}}$ and $B\to Kν{\barν}$, suggest possible lepton flavor universality violation and new exotic interactions. In this work, we explore these anomalies within a non-minimal SU(5) grand unified theory (GUT) framework, which introduces a 45-dimensional Higgs representation predicting exotic scalar particles, including the leptoquark $R_2$ and diquark $S_6$. The $R_2$ leptoquark addresses charged current anomalies in $b\to cτν$ transitions, the $S_6$ diquark contributes to nonleptonic neutral current processes, such as $B\to Kπ$, while at the loop level, diagrams involving the exchanges of the leptoquark, diquark, and the Standard Model particles contribute to $B\to Kν{\barν}$, offering solutions to longstanding puzzles.

hep-ph↗

arXiv2026

Fermionic Dark Matter and New Scalar Production in $e^+e^- \to H^+H^-$ at Colliders

We investigate the pair production process $e^+e^- \to H^+H^-$ in the framework of the scotogenic model. The production mechanism receives contributions at tree level from photon and $Z$-boson exchange, as well as from $t$-channel exchange of the new singlet right-handed fermions $N_{1,2,3}$. where neutrino masses are generated radiatively and one of the singlet right-handed fermions serves as a viable dark matter candidate. We evaluate the individual contributions of these diagrams and compute the total production cross section after imposing all relevant theoretical and experimental constraints on the model parameters, including those associated with dark matter relic abundance and direct detection limits. Our results demonstrate that the dominant contribution to the cross section originates from the exchange of the singlet fermions $N_{1,2,3}$, particularly from the dark matter component of the spectrum. In addition, we examine the dependence of the cross section on the center-of-mass energy for several benchmark scenarios in the allowed parameter space. These predictions can be probed at future high-energy $e^+e^-$ colliders, providing a sensitive test of the scotogenic framework and the role of fermionic dark matter, as well as enabling more stringent constraints on the model parameters.

hep-ph↗

arXiv2025

Dark Higgs in Hidden Sector as a Probe for Dark Matter

This study presents a sensitivity analysis of exotic Higgs boson decays at the electron--positron stage of the Future Circular Collider (FCC-ee), performed within the FCCAnalyses framework. The analysis investigates Higgs boson production in association with a Z boson in electron--positron collisions at a center-of-mass energy of 240~GeV. The Higgs boson is assumed to decay into a pair of long-lived scalar particles, while the Z boson decays leptonically. A hadronic final state is considered, in which the long-lived scalars subsequently decay into bottom--antibottom quark pairs. The simulation chain is implemented using the FCCAnalyses framework, with event generation performed using \textsc{MadGraph} and \textsc{Pythia}, and detector effects modeled with \textsc{Delphes}. Displaced vertices arising from the decays of long-lived particles are reconstructed using the FCCAnalyses implementation of the \textsc{LCFIPlus} secondary vertex finding algorithm, enhanced with extended features such as customized track selection. The final event selection requires the reconstruction of a Z boson together with at least two displaced vertices. This strategy efficiently suppresses Standard Model backgrounds while retaining at least three expected signal events, including statistical uncertainties, over most of the explored parameter space. The study considers scalar masses of 20~GeV and 60~GeV and mixing angles of $10^{-5}$, $10^{-6}$, and $10^{-7}$. The results demonstrate that FCC-ee will be sensitive to long-lived scalars with decay lengths ranging from approximately 1~mm to 10~m, with optimal sensitivity around a decay length of 0.3~m.

hep-ex↗

arXiv2023

CP Asymmetry in $τ\to Kπν_τ $ within Non-Minimal $SU(5)$

Direct CP asymmetry in semi-leptonic $τ$ decays is an intriguing hint for new physics beyond the standard model. We investigate the CP asymmetry in $τ^- \to K_S^0 π^- ν_τ$ and $τ^- \to K^- π^0 ν_τ$ decays in non-minimal SU(5) model, with 45-dimensional Higgs multiplet. We show that the associate color-triplet scalar is a natural example of a scalar leptoquark that mediates the transition $τ\to s \bar u ν_τ$, and accounts for the 2.8 $σ$ discrepancy between the $A_{\rm CP}(τ^- \to K_S^0 π^- ν_τ)$ experimental results and the SM expectation. Furthermore, it predicts a sizable $A_{\rm CP}(τ^- \to K^- π^0 ν_τ)$, of order ${\cal O}(10^{-3})$, which can be accessible in current and near future experiments.

hep-ph↗

arXiv2022

Thermodynamic and cosmological parameters of early stages of the Universe

The early Universe was characterized by the presence of heavy particles that decoupled at different temperatures leading to different phases of the Universe. This had a consequences on the time evolution of the thermodynamic and the cosmological parameters characterizing each phase of the early Universe. In this study, we derive the analytic expressions of the equations governing the time evolution of these parameters in the early eras of the Universe namely, the radiation era, the quark-gluon plasma era, the hadron era and the mixed era. The parameters under concern include the energy density, the entropy density, the temperature, the pressure in addition to Hubble parameter and the scale factor. Having these expressions allows us to give estimations of the times corresponding to the beginning and ending of each era of the Universe as will be presented in this work.

hep-ph↗

arXiv2021

Phenomenology of the Hidden SU(2) Vector Dark Matter Model

We investigate the phenomenology of an extension of the Standard Model (SM) by a non-abelian gauge group $SU(2)_{HS}$ where all SM particles are singlets under this gauge group, and a new scalar representation $ϕ$ that is singlet under SM gauge group and doublet under $SU(2)_{HS}$. In this model, the dark matter (DM) candidates are the three mass degenerate dark photons $A_{i}$ $(i=1,2,3)$ of $SU(2)_{HS}$; and the hidden sector interacts with the (SM) particles through the Higgs portal interactions. Consequently, there will be a new CP-even scalar $η$ that could be either heavier or lighter than the SM-like Higgs. By taking into account all theoretical and experimental constraints such as perturbativity, unitarity, vacuum stability, non-SM Higgs decays, DM direct detection, DM relic density, we found viable DM is possible in the range from GeV to TeV. Within the viable parameters space, the both of the triple Higgs coupling and the di-Higgs production at LHC14 could be enhanced or reduced depending on the scalar mixing and the mass of the scalar particle $η$.

hep-ph↗

arXiv2021

Exploring charm decays with missing energy in leptoquark models

We investigate the possibility that scalar leptoquarks generate consequential effects on the flavor-changing neutral-current decays of charmed hadrons into final states with missing energy ($\not\!\!E$) carried away by either standard model or sterile neutrinos. We focus on scenarios involving the $R_2$, $\tilde R_2$, and $\bar S_1$ leptoquarks and take into account various pertinent constraints, learning that meson-mixing ones and those inferred from collider searches can be of significance. We find in particular that the branching fractions of charmed meson decays $D\to M\!\not\!\!E$, $M=π,ρ$, and $D_s\to K^{(*)}\!\not\!\!E$ and singly charmed baryon decays $Λ_c^+\to p\!\not\!\!E$ and $Ξ_c\toΣ\!\not\!\!E$ are presently allowed to attain the $10^{-7}$-$10^{-6}$ levels if induced by $R_2$ and that the impact of $\tilde R_2$ is comparatively much less. In contrast, the contributions of $\bar S_1$, which couples to right-handed up-type quarks and the sterile neutrinos, could lead to branching fractions as high as order $10^{-3}$. This suggests that these charmed hadron decays might be within reach of the BESIII and Belle II experiments or future super charm-tau factories and could serve as potentially promising probes of leptoquark interactions with sterile neutrinos.

hep-ph↗

arXiv2021

Exploring new physics contributions to $CP$ violation in $τ^- \to K^-π^0ν_τ $

A general analysis of possible violation of CP in processes like $τ\to Kπν$, for unpolarized $τ$ is presented. In this paper, we derive the new contributions to the effective Hamiltonian governs $\vertΔS \vert=1$ semileptonic tau decays in the framework of two Higgs doublet model with generic Yukawa structure and Leptoquarks models. Within these models, we list all operators, in the effective Hamiltonian and provide analytical expression for their corresponding Wilson coefficients. Moreover, we analyze the role of the different contributions, originating from the scalar, vecor and tensor hadronic currents, in generating direct CP asymmetry in the decay rate of $τ^-\to K^-π^0ν_τ$. We show that non vanishing direct CP asymmetry in the decay rate of $τ^-\to K^-π^0ν_τ$ can be generated due to the presence of both, the weak phase in the Wilson coefficient corresponding to the tensor operator and the strong phase difference resulting from the interference between the form factors expressing the matrix elements of the vector and tensor hadronic currents. After taking into account all relevant constraints, we find that the generated direct CP asymmetry is of order $10^{-8}$ which is several orders of magnitude larger than the standard model prediction. We show also that, in two Higgs doublet model with generic Yukawa structure , direct local or non integrated CP violation can be as large as $0.3$ % not far from experimental possibilities. This kind of asymmetry can be generated due to the interference between vector and scalar contributions with different weak phases which is not the case in the SM.

hep-ph↗

arXiv2020

Beyond SM Physics and searches for SUSY at the LHC

This is the written version of a talk given by S.K. at the $10^{th}$ International Conference on High Energy and Astroparticle, Constantine, Algeria. We briefly review the Standard Model (SM) and the major evidences and main direction of physics beyond the SM (BSM). We introduce supersymmetry, as one of the well-motivated BSM. Basic introduction to Minimal Supersymmetric Standard Model (MSSM) is given. We analyze the thermal relic abundance of lightest neutralino, which is the Lightest Supersymmetric Particle (LSP) in the MSSM. We show that the combined Large Hadron Collider (LHC) and relic abundance constraints rule out most of the MSSM parameter space except a very narrow region. We also review non-minimal SUSY model, based on the gauge group $SU(3)_C \times SU(2)_L \times U(1)_Y \times U(1)_{B-L}$ (BLSSM), where an Inverse Seesaw mechanism of light neutrino mass generation is naturally implemented. The phenomenological implications of this type of model at the Large Hadron Collider (LHC) are analyzed.

hep-ph↗

arXiv2019

New Physics signature in $D^0 (\bar{D}^0)\to f$ effective width asymmetries

Violation of charge conjugation-parity ($\rm CP$) symmetry plays a major rule in the dominance of matter in our universe. A kind of $\rm CP$ violation results from the asymmetry of the life time measured in $M^0$ and $\bar M^0$, here $M$ is a heavy meson, decays to final states which is referred in the literature as $A_Γ^f$. In this paper, we give an estimation of the upper bound on $|A_Γ^f|$ for the Cabibbo Favored $D^0 \rightarrow K^- π^+$ decay process in different models. We show that in the standard model, $|A_Γ^f| \lesssim\mathcal{O} (10^{-10})$. Recently a bound on $A_Γ^f$ has been obtained: $(A^f_Γ)^{Exp.}= (1.6 \pm 1)\times 10^{-4}$. This result motivates further studies on $A_Γ^f$ in beyond standard model physics. In the framework of two Higgs doublet model with generic Yukawa structure, we show that $|A_Γ^{f}|\lesssim \mathcal{O} (10^{-7})$ which is several orders of magnitude smaller than the current experimental value. Finally, in the framework of left-right symmetric models in which the mixing between the left and the right gauge bosons is allowed and the left-right symmetry is not manifest at unification scale, we find that $A_Γ^f$ can be as large as $|A_Γ^f|\lesssim\mathcal{O} (10^{-5})$ which is one order of magnitude smaller than the experimentally measured value by LHCb collaborators.

hep-ph↗

arXiv2019

Rare nonleptonic $\bar{B}_s^0$ decays as probes of new physics behind $b\to sμ\barμ$ anomalies

The anomalous results of recent measurements on various $b\to sμ^+μ^-$ processes could be initial evidence of physics beyond the standard model (SM). Assuming this to be the case, we entertain the possibility that the underlying new physics also affects the rare nonleptonic decays of the $\bar B_s^0$ meson. We consider in particular new physics arising from the interactions of a heavy $Z'$ boson and investigate their influence on the decay modes $\bar B_s^0\to(η,η',ϕ)ω$, which receive sizable QCD- and electroweak-penguin contributions. These decays are not yet observed, and their rates are estimated to be relatively small in the SM. Taking into account the pertinent constraints, we find that the $Z'$ effects can greatly increase the rates of $\bar B_s^0\to(η,ϕ)ω$, by as much as two orders of magnitude, with respect to the SM expectations. We have previously shown that $\bar B_s^0\to(η,ϕ)π^0$, with similarly suppressed SM rates, could also undergo substantial $Z'$-induced enhancement. These rare modes can therefore serve as complementary probes of the potential new physics which may be responsible for the $b\to sμ^+μ^-$ anomalies.

hep-ph↗

arXiv2019

Direct CP violation in $D^+ \to K^0(\bar K^0) π^+$ decays as a probe for new physics

In this paper we investigate CP violation in charged decays of $D$ meson. Particularly, we study the direct CP asymmetry of the Cabibbo favored non-leptonic $D^+ \rightarrow \bar K^0 π^+$ and the doubly Cabibbo-suppressed decay mode $D^+ \rightarrow K^0 π^+$ within standard model, two Higgs doublet model with generic Yukawa structure and left right symmetric models. In the standard model, we first derive the contributions from box and di-penguin diagrams contributing to their amplitudes which are relevant to the generation of the weak phases essential for non-vanishing direct CP violation. Then, we show that these phases are so tiny leading to a direct CP asymmetry of order $10^{-11}$ in both decay modes. Regarding the two Higgs doublet model with generic Yukawa structure and after taking into account all constraints on the parameter space of the model, we show that the enhanced direct CP asymmetries can be 6 and 7 orders of magnitudes larger than the standard model prediction for $D^+ \rightarrow \bar K^0 π^+$ and $D^+ \rightarrow K^0 π^+$ respectively. Finally, within left right symmetric models, we find that sizable direct CP asymmetry of ${\mathcal O } (10^{-3})$ can be obtained for the decay mode $D^+ \rightarrow \bar K^0 π^+$ after respecting all relevant constraints.

hep-ph↗

arXiv2018

Connecting $b\to s\ell\bar\ell$ anomalies to enhanced rare nonleptonic $\bar{B}_s^0$ decays in $Z'$ model

The present data on a number of observables in $b\to sμ^+μ^-$ processes manifest some tensions with the standard model (SM). Assuming that these anomalies have a new physics origin, we consider the possibility that a $Z'$ boson is responsible for them. We further assume that its interactions with quarks also affect rare nonleptonic decays of the $\bar B_s^0$ meson which are purely isospin-violating and tend to be dominated by electroweak-penguin contributions, namely $\bar B_s^0\to(η,η',ϕ)(π^0,ρ^0)$. Most of these decays are not yet observed, and their rates are expected to be relatively small in the SM. Taking into account constraints from various measurements, including the evidence for $\bar B_s^0\toϕρ^0$ recently seen by LHCb, we find that the $Z'$ effects on $\bar B_s^0\to(η,ϕ)π^0$ can make their rates bigger than the SM predictions by up to an order of magnitude. For $\bar B_s^0\toη'π^0,(η,η')ρ^0$, the enhancement factors are at most a few. Since the $Z'$ contributions to the different channels depend on different combinations of its couplings, observations of more of these decays in future experiments, along with improved $b\to sμ^+μ^-$ data, will probe this $Z'$ scenario more thoroughly.

hep-ph↗

arXiv2017

CP violation in $D^0 \to K^+ π^- $

In this paper we study the direct CP asymmetry of the doubly Cabibbo-suppressed decay mode $D^0 \to K^+ π^- $ within standard model and two Higgs doublet model with generic Yukawa structure. In the standard model we derive the corrections to the tree level amplitude, generated from the box and di-penguin diagrams, required for generating the weak CP violating phases. We show that these phases are so tiny leading to a direct CP asymmetry of order $10^{-9}$. Regarding the two Higgs doublet model with generic Yukawa structure we derive the Wilson coefficients relevant to $D^0 \to K^+ π^- $. After taking into account all constraints on the parameter space of the model we show that charged Higgs couplings to quarks can lead to a direct CP asymmetry of order $10^{-3}$ which is $6$ orders of magnitude larger than the standard model prediction.

hep-ph↗

arXiv2017

New physics contributions to $\bar{B}_s \rightarrow π^0(ρ^0 )\,η^{(')} $ decays

The decay modes $\bar{B}_s \rightarrow π^0(ρ^0 )\,η^{(')} $ are dominated by electroweak penguins that are small in the standard model. In this work we investigate the contributions to these penguins from a model with an additional $U(1)'$ gauge symmetry and show there effects on the branching ratios of $\bar{B}_s \rightarrow π^0(ρ^0 )\,η^{(')} $. In a scenario of the model, where $Z^\prime$ couplings to the left-handed quarks vanish, we show that the maximum enhancement occurs in the branching ratio of $\bar B^0_s\to \,π^0\,η'$ where it can reach $6$ times the SM prediction. On the other hand, in a scenario of the model where $Z^\prime$ couplings to both left-handed and right-handed quarks do not vanish, we find that $Z^\prime$ contributions can enhance the branching ratio of $B^0_s\to\,ρ^0\,η$ up to one order of magnitude comparing to the SM prediction for several sets of the parameter space where both $ ΔM_{B_s}$ and $S_{ψϕ}$ constraints are satisfied. This kind of enhancement occurs for a rather fine-tuned point where $ ΔM_{B_s}$ constraint on $\mid S_{SM} (B_s) + S_{Z'} (B_s)\mid $ is fulfilled by overcompensating the SM via $S_{Z'} (B_s) \simeq -2 S_{SM} (B_s)$.

hep-ph↗

arXiv2017

Exploring high-mass diphoton resonance without new colored states

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 $\tilde s$, 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 $σ(pp\rightarrow\tilde{s}\rightarrowγγ)$ 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 $\tilde s$ which are potentially testable in upcoming LHC measurements.

hep-ph↗

arXiv2016

Analysis on a Nambu--Jona-Lasinio Model of Dynamical Supersymmetry Breaking

This is a report on our newly proposed model of dynamical supersymmetry breaking with some details of the analysis involved. The model in the simplest version has only a chiral superfield (multiplet), with a strong four-superfield interaction in the Kähler potential that induces a real two-superfield composite with vacuum condensate. The latter has supersymmetry breaking parts, which we show to bear nontrivial solution following basically a standard nonperturbative analysis for a Nambu--Jona-Lasinio type model on a superfield setting. The real composite superfield has a spin one component but is otherwise quite unconventional. We discuss also the parallel analysis for the effective theory with the composite. Plausible vacuum solutions are illustrated and analyzed. The supersymmetry breaking solutions have generated soft mass(es) for the scalar avoiding the vanishing supertrace condition for the squared-masses of the superfield components. We also present some analysis of the resulted low energy effective theory with components of the composite become dynamical. The determinant of the fermionic modes is shown to be zero illustrating the presence of the expected Goldstino. The model gives the possibility of constructing a supersymmetric standard model with all (super)symmetry breaking masses generated dynamically and directly without the necessity of complicated hidden or mediating sectors.

hep-th↗

arXiv2015

Effects of Two Inert Scalar Doublets on Higgs Interactions and Electroweak Phase Transition

We study some implications of the presence of two inert scalar doublets which are charged under a dark Abelian gauge symmetry. Specifically, we investigate the effects of the new scalars on oblique electroweak parameters and on the interactions of the 125 GeV Higgs boson, especially its decay modes $h\toγγ,γZ$, and trilinear coupling, all of which will be probed with improved precision in future Higgs measurements. Moreover, we explore how the inert scalars may give rise to strongly first-order electroweak phase transition and also show its correlation with sizable modifications to the Higgs trilinear coupling.

hep-ph↗