arXiv subjects

Shaaban Khalil

Publications and source records attributed to Shaaban Khalil.

At least 37 records · Page 2Linked to original sources

arXiv2024

Higgs Quadruplet Impact on $W$ Mass Shift, Dark Matter, and LHC Signatures

The addition of a Higgs quadruplet to the standard model (SM) of quarks and leptons would shift the $W$ boson mass upward. It could also facilitate the production of dark matter through the conventional thermal freeze-out scenario via Yukawa interaction with the Higgs quadruplet or freeze-in production from the decay of SM Higgs. We investigate the same-sign lepton smoking gun signature of the double-charged scalar component of the Quadruplet Higgs at the LHC.

hep-ph↗

arXiv2024

Modular $A_4$ Symmetry With Three-Moduli and Flavor Problem

The modular $A_4$ symmetry with three moduli is investigated. We assign different moduli to charged leptons, neutrinos, and quarks. We analyze these moduli at their fixed points where a residual symmetry exists. We consider two possibilities for right-handed neutrinos. First, they are assumed to be singlets under modular symmetry. In this case, we show that the lepton masses and mixing can be obtained consistently with experimental observations. Second, they are assigned non-trivially under modular symmetry. We emphasize that a small deviation from their fixed point is required in this case. Finally, the quark masses and mixing are generated correctly around the fixed point of their modulus. In our analysis, we only consider the simple case of weight 2.

hep-ph↗

arXiv2023

Primordial Gravitational Waves in Generalized Palatini Gravity

Extended Palatini gravity is the metric-affine gravity theory characterized by zero torsion, nonzero metricity and a quadratic of the antisymmetric Ricci curvature. It reduces dynamically to general relativity plus a geometric Proca field. In this work, we study imprints of the geometric Proca field in the gravitational waves . Our results show that the geometric Proca leaves significant signatures in the gravitational wave signal, and gravitational wave energy density is large enough to be detectable by the next upgrade of the existing GW detectors. Our results, if confirmed observationally, will be an indication that the gravity could well non-Riemannian in nature.

gr-qc↗

arXiv2023

TeV-scale leptoquark searches at the LHC and their E$_6$SSM Interpretation

We perform a model-independent search for leptoquarks (LQs) at the Large Hadron Collider through their pair-production and subsequent decay into $t\bar t ττ$ intermediate states. We show that, assuming full luminosity of the Run 2, a fully hadronic signal emerging from this intermediate state can surpass in sensitivity the established searches relying on leptons in the final state. Our conclusion is supported by a thorough Monte-Carlo analysis, and we advocate the deployment of our proposed search channel in the proper experimental setting of the Run 3. Furthermore, in order to highlight the full scope of this approach for constraining LQ theories, we interpret our results in the context of the string-inspired Exceptional Supersymmetric Standard Model, which naturally predicts the $S_1-$type scalar LQ states that we analyse here.

hep-ph↗

arXiv2023

Light $Z'$ Signatures at the LHC

In this work, we discuss a distinctive $pp\to {\rm Higgs}\to Z'Z'\to 4l$ ($l=e,μ$) signal at the Large Hadron Collider (LHC), where the `Higgs' label refers to the SM-like Higgs state discovered in 2012 or a lighter one in the framework of a theoretical model embedding a spontaneously broken $U(1)'$ symmetry in addition to the Standard Model (SM) gauge group. The additional $U(1)'$ symmetry generates a very light $Z'$ state, with both vector and axial (non-universal) couplings to fermions, which are able to explain the so-called Atomki anomaly, compliant with current measurements of the Anomalous Magnetic Moments (AMMs) of electron and muon as well as beam dump experiments. We show that the cross section for this process should be sufficiently large to afford one with significant sensitivity during Run 3 of the LHC.

hep-ph↗

arXiv2022

Explaining the ${\mathcal{R}}(D)$ and ${\mathcal{R}}(D^{\ast})$ Anomalies in the $B-L$ Supersymmetric Standard Model with Inverse Seesaw

We investigate the ${\mathcal{R}}(D)$ and ${\mathcal{R}}(D^{\ast})$ anomalies in the context of the $B-L$ extension of the Minimal Supersymmetric Standard Model with Inverse Seesaw. We demonstrate that the lepton penguin $W^{\pm}l \barν_l $ ($l=e,μ,τ$) mediated by CP-even/odd right-handed sneutrinos, charginos and neutralinos can account for these anomalies simultaneously.

hep-ph↗

arXiv2022

Nested Radiative Seesaw Masses for Dark Matter and Neutrinos

The scotogenic model of neutrino mass is modified so that the dark Majorana fermion singlet $S$ which makes the neutrino massive is itself generated in one loop. This is accomplished by having $Z_6$ lepton symmetry softly broken to $Z_2$ in the scalar sector by a unique quadratic term. It is shown that $S$ is a viable freeze-in dark-matter candidate through Higgs decay.

hep-ph↗

arXiv2022

The 28 GeV Dimuon Excess in Lepton Specific 2HDM

We explore the Higgs mass spectrum in a class of Two Higgs Doublet Models (THDMs) in which a scalar SU(2)_L doublet interacts only with quarks, while the second one interacts only with leptons. The spectrum includes two CP-even Higgs bosons, either of which can account for the SM-like Higgs boson, and the spectra involving light Higgs bosons receive strong impacts from the LEP results and the current collider analyses. We find that a consistent spectrum can involve a CP-odd Higgs boson as light as about 10 GeV, while the lightest CP-even Higgs boson cannot be lighter than about 55 GeV when m_A ~ 28 GeV. These analyses can rather bound the low tan beta region which can also accommodate an observed excess in dimuon events at m_mumu ~ 28 GeV. A lepton-specific class of THDMs (LS-THDM) can predict such an excess through A -> mu mu decays, while the solutions can be constrained by the A -> tau tau mode. After constraining the solutions with the consistent ranges of sigma(pp -> bbA -> bb tau tau), a largest excess at about 1.5 sigma at 8 TeV center of mass (COM) energy and 2 sigma at 13 TeV COM is observed for tan beta ~ 12 and m_A ~ 28 GeV in the sigma(pp -> bbA -> bb mu mu) events.

hep-ph↗

arXiv2022

A combined approach to the analysis of space and ground experimental data within a simplified E6SSM

Within the Exceptional Supersymmetric Standard Model (E6SSM), we investigate striking signatures at the Large Hadron Collider (LHC) for a long-lived charged inert higgsino, which is degenerate with the inert neutralino at tree level and a mass splitting of order O(0.3) GeV is generated at the loop level, resulting in a lifetime of order O(0.02) nanoseconds. We focus on the most sensitive search for long-lived charged inert higgsino decays to the lightest neutral inert higgsino Dark Matter (DM) and very soft charged leptons, which are eventually stopped in the detector resulting in a disappearing-track signal. Furthermore, we study the displaced vertex signature of the inert chargino in the case where it is produced via the Z' portal. We illustrate how difficult it is to construct displaced vertices in this class of models, though some evidence of these could be gained at the High Luminosity LHC. Finally, we compare the spin independent and spin dependent cross sections of the lightest inert higgsino DM to those of current direct detection experiments, proving that it is possible to gain sensitivity to the active DM component of this scenario in the near future. The combination of these signatures with the one emerging from Z' production and decay via Drell-Yan, which can be characterised as belonging to the E6SSM via both the cross section and Forward-Backward Asymmetry, could point uniquely to this non-minimal realisation of supersymmetry. In fact, we remark that these evidences of the E6SSM can also be correlated to the features of standard SUSY cascades in terms of the amount of missing transverse energy present therein.

hep-ph↗

arXiv2022

The muon $g-2$ in an Aligned 2-Higgs Doublet Model with Right-Handed Neutrinos

In this note, we show how one can attribute the anomaly currently present in the measurement of the anomalous magnetic moment of the muon ($a_μ$) to the presence of an underlying Aligned 2-Higgs Doublet Model (A2HDM) with Right-Handed (RH) neutrinos, $ν_R$. The effects of the latter scenario are driven by one and two-loop topologies wherein a very light CP-odd neutral Higgs state ($A$) contributes significantly to $a_μ$. Over the region of parameter space of our new physics model which explains the aforementioned anomaly, also consistent with the most recent measurements of the electron anomalous magnetic moment ($a_e$), wherein the charged Higgs state $H^\pm$ plays a similar role, we predict an almost background-free hallmark signature of it, due to $H^\pm A$ production followed by Higgs boson decays yielding multi-$τ$ final states, which can be already be searched for at the Large Hadron Collider (LHC).

hep-ph↗

arXiv2021

Predestined Dark Matter Varieties in the Simplest Left-Right Model

In the simplest left-right extension of the Standard Model of particle interactions with one scalar bidoublet and one $SU(2)_R$ triplet for seesaw Majorana neutrino masses, the addition of a variety of fermion and scalar multiplets automatically makes them stable (predestined) dark matter candidates. We discuss the interplay of this dark ensemble in relic abundance and direct searches.

hep-ph↗

arXiv2021

Monophoton signals in electron-positron colliders in a simplified E6SSM

The mono-photon signature emerging in an E6 Supersymmetric Standard Model (E6SSM) from inert higgsino Dark Matter (DM) is analyzed at future $e^+e^-$ colliders. As the inert neutral and charged higgsinos are nearly degenerate, the inert chargino is a rather long lived particle and the charged particle associated with its decay to the inert higgsino is quite soft. We show that the pair production of inert charginos at a 500 GeV electron-positron collider with an initial or final state photon is the most promising channel for probing the inert higgsino as one DM candidate within the E6SSM. We also emphasize that this signal has no chance of being observed at the Large Hadron Collider with higher energy and/or luminosity. Finally, we remark that, combined with a DM signal produced in Direct Detection experiments involving an active higgsino state as the second DM candidate, this dual evidence could point to a two-component DM version of the E6SSM.

hep-ph↗

arXiv2020

Quantum Cosmology with vector torsion

We extend the treatment of quantum cosmology to a manifold with torsion. We adopt a model of Einstein-Cartan-Sciama-Kibble compatible with the cosmological principle. The universe wavefunction will be subject to a $\mathcal{PT}$-symmetric Hamiltonian. With a vanishing energy-momentum tensor, the universe evolution in the semiclassical and classical regimes is shown to reflect a two-stage inflationary process induced by torsion.

gr-qc↗

arXiv2020

Explaining electron and muon $g-2$ anomalies in an Aligned 2-Higgs Doublet Model with Right-Handed Neutrinos

We explain anomalies currently present in various data samples used for the measurement of the anomalous magnetic moment of electron ($a_e$) and muon ($a_μ$) in terms of an Aligned 2-Higgs Doublet Model with right-handed neutrinos. The explanation is driven by one and two-loop topologies wherein a very light CP-odd neutral Higgs state ($A$) contributes significantly to $a_μ$ but negligibly to $a_e$, so as to revert the sign of the new physics corrections in the former case with respect to the latter, wherein the dominant contribution is due to a charged Higgs boson ($H^\pm$) and heavy neutrinos with mass at the electroweak scale. For the region of parameter space of our new physics model which explains the aforementioned anomalies we also predict an almost background-free smoking-gun signature of it, consisting of $H^\pm A$ production followed by Higgs boson decays yielding multi-$τ$ final states, which can be pursued at the Large Hadron Collider.

hep-ph↗

arXiv2020

Di-photon decay of a light Higgs state in the BLSSM

In the context of the $B-L$ Supersymmetric Standard Model (BLSSM), we investigate the consistency of a light Higgs boson, with mass around $90-95$ GeV, with the results of a search performed by the CMS collaboration in the di-photon channel at the integrated luminosity of 35.9 fb$^{-1}$ and $\sqrt s$ = 13 TeV.

hep-ph↗

arXiv2020

Multi-component Dark Matter in a Simplified E$_6$SSM Model

We study Dark Matter (DM) in the Exceptional Supersymmetric Standard Model (E$_6$SSM). The model has both active and inert Higgs superfields and by imposing discrete symmetries one can generate two DM candidates. We show that the lightest higgsinos of the active and inert sectors give a viable setup for two-component DM. We also illustrate the scope of both direct and indirect detection experiments in extracting such a DM sector. Future experiments of the former kind have a good chance of finding the active component while the inert higgsino will be very hard to detect while those of the latter kind will have no sensitivity to either candidate.

hep-ph↗

arXiv2020

$R_K$ and $R_{K^*}$ in an Aligned 2HDM with Right-Handed Neutrinos

We consider the possibility to explain the recent $R_K$ and $R_{K ^*}$ anomalies in a 2-Higgs Doublet Model, known as Aligned, combined with a low scale seesaw mechanism generating light neutrino masses and mixings. In this class of models, a large Yukawa coupling allows for significant non-universal leptonic contributions, through box diagrams mediated by charged Higgs bosons and right-handed neutrinos, to the $b \to s \ell^+ \ell^-$ transition that can then account for both $R_K$ and $R_{K^*}$ anomalies.

hep-ph↗

arXiv2020

Gauge-Field-Induced Torsion and Cosmic Inflation

Inflation in the framework of Einstein-Cartan theory is revisited. Einstein-Cartan theory is a natural extension of the General Relativity, with non-vanishing torsion. The connection on Riemann-Cartan spacetime is only compatible with the cosmological principal for a particular form of torsion. We show this form to also be compatible with gauge invariance principle for a non-Abelian and Abelian gauge fields under a certain deviced minimal coupling procedure. We adopt an Abelian gauge field in the form of "cosmic triad". The dynamical field equations are obtained and shown to sustain cosmic inflation with a large number of e-folds. We emphasize that at the end of inflation, torsion vanishes and the theory of Einstein-Cartan reduces to the General Relativity with the usual FRW geometry.

hep-th↗