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S. Khalil

Publications and source records attributed to S. Khalil.

At least 19 recordsLinked to original sources
arXiv2023

Searching for a Heavy Neutral CP-Even Higgs Boson in the BLSSM at the LHC Run 3 and HL-LHC

The detection of a heavy neutral CP-even Higgs boson of the $B-L$ Supersymmetric Standard Model (BLSSM), $h'$, with $m_{h'}\simeq 400~\text{GeV}$, at the Large Hadron Collider (LHC) for a center-of-mass energy of $\sqrt{s}=14~\text{TeV}$, is investigated. The following production and decay channels are considered: $gg\to h'\to{ZZ}\to4\ell$ and $gg\to h'\to{W^+W^-}\to2\ell+\slashed{E}_T$ (with $\slashed{E}_T$ being the Missing~Transverse~Energy~(MET)), where $\ell=e,\mu$, with integrated luminosity $L_{\text{int}}=300~{\text{fb}}^{-1}$ (Run 3). Furthermore, we also look into the di-Higgs channel $gg\to h'\to{hh}\to{b\bar{b}\gamma\gamma}$ at the High-Luminosity LHC (HL-LHC) with an integrated luminosity of $L_{\text{int}}=3000~{\text{fb}}^{-1}$. We demonstrate that promising signals with high statistical significance can be obtained through the three aforementioned channels.

hep-ph↗
arXiv2023

CP Asymmetry in $\tau \to K\pi \nu_{\tau} $ within Non-Minimal $SU(5)$

Direct CP asymmetry in semi-leptonic $\tau$ decays is an intriguing hint for new physics beyond the standard model. We investigate the CP asymmetry in $\tau^- \to K_S^0 \pi^- \nu_\tau$ and $\tau^- \to K^- \pi^0 \nu_\tau$ 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 $\tau \to s \bar u \nu_\tau$, and accounts for the 2.8 $\sigma$ discrepancy between the $A_{\rm CP}(\tau^- \to K_S^0 \pi^- \nu_\tau)$ experimental results and the SM expectation. Furthermore, it predicts a sizable $A_{\rm CP}(\tau^- \to K^- \pi^0 \nu_\tau)$, of order ${\cal O}(10^{-3})$, which can be accessible in current and near future experiments.

hep-ph↗
arXiv2023

Resolving $R_{D}$ and $R_{D^*}$ Anomalies in Adjoint SU(5)

We investigate the $R_{D}$ and $R_{D^*}$ anomalies in the context of non-minimal $SU(5)$, where Higgs sector is extended by adjoint 45-dimensional multiplet. One of the light spectrum of this model could be the scalar triplet leptoquark that is contained in this multiplet. We demonstrate that this particular scalar leptoquark mediation of the transition $b \to c \tau \nu$ is capable of simultaneously accounting for both $R_{D}$ and $R_{D^*}$ anomalies. We further emphasize that another Yukawa coupling controls its contribution to $b \to s \ell^+ \ell^-$, ensuring that $R_K$ and $R_{K^*}$ remain consistent with the standard model predictions.

hep-ph↗
arXiv2022

Search for Mono-Higgs Signals in $b\bar b$ Final States Using Deep Neural Networks

We study mono-Higgs signatures emerging in an illustrative new physics scenario involving Standard Model Higgs boson decays to bottom quark pairs using Hybrid Deep Neural Networks. We use a Multi-Layer Perceptron to analyze the kinematic observables and optimize the signal-to-background discrimination. The global color flow structure of hard jets emerging from the decay of heavy particles with different color charges is crucial to single out the mono-Higgs signature. Upon embedding the different color flow structures for signal and backgrounds into constructed images, we use a Convolution Neural Network to analyze the latter. Specifically, the approach takes initially a mono-type data as input, frittering away invaluable multi-source and multi-scale information. We then discuss a general architecture of Hybrid Deep Neural Networks that supports instead mixed input data. In comparison with single input Deep Neural Networks, like MultiLayers Perceptron or Convolution Neural Network, the Hybrid Deep Neural Networks provide higher capacity in feature extraction and thus in signal vs background classification performance. We provide reference results for the case of the High-Luminosity Large Hadron Collider.

hep-ph↗
arXiv2022

Muon $g-2$ anomaly in a left-right model with an inverse seesaw mechanism

We investigate the possibility of explanation for the muon anomalous magnetic moment $g_\mu-2$ in a left-right model with an inverse seesaw mechanism. We emphasize that the observed deviation from the Standard Model predictions can be accommodated in a large part of the parameter space of this class of models, where loops with massive neutrinos and charged Higgs boson as well as the weak $W$ boson contribute significantly to $g_\mu-2$. Stringent constraints due to lepton flavor violation $\mu\to{e}\gamma$, $\mu$-${e}$~conversion and the electron anomalous magnetic moment $g_e-2$ are considered, and the results are compatible.

hep-ph↗
arXiv2022

Investigating $R_D$ and $R_{D^*}$ anomalies in a Left-Right model with an Inverse Seesaw

We investigate $R_D$ and $R_{D^*}$ anomalies in a low scale left-right symmetric model based on $SU(3)_C\times SU(2)_L\times SU(2)_R\times U(1)_{B-L}$ with a simplified Higgs sector consisting of only one bidoublet and one $SU(2)_R$ doublet. The Wilson coefficients relevant to the transition $b\to c\tau \nu$ are derived by integrating out the charged Higgs $H^\pm$ boson, which gives the dominant contributions. We emphasize that the charged Higgs effects, with the complex right-handed quark mixing matrix, can account for both $R_D$ and $R_{D^*}$ anomalies simultaneously, while adhering to a set of significant constraints including, for instance, ${\rm BR}(B^-_c \to \tau^- \bar{\nu}_\tau) $ and $B_{s(d)}-\bar B_{s(d)}$ mixing. In relation to this, we show that the predicted values of the $D^\ast$, $\tau$ longitudinal polarizations and $P_\tau (D)$ can be affected for the set of the parameters of the model resolving the $R_{D,D^\ast}$ anomalies.

hep-ph↗
arXiv2021

Search for a heavy neutral Higgs boson in a left-right model with an inverse seesaw mechanism at the LHC

We develop a low scale left-right symmetric model based on $SU(3)_C\times SU(2)_L\times SU(2)_R\times U(1)_{B-L}\times Z_2$ with a simplified Higgs sector consisting of only one bidoublet and one $SU(2)_R$ doublet. In this model, the tiny values of light neutrino masses are generated through an inverse-seesaw mechanism. We emphasize that in this setup, the tree-level flavor changing neutral current can be strongly suppressed, consistent with the current experimental constraints. We show that the lightest $CP$-even Higgs boson, which is like the standard model Higgs boson, and the next lightest Higgs boson, $h'$, are generated from the neutral components of the bidoublet. We show that the mass of the next lightest Higgs boson can be of an order a few hundred~\text{GeVs}. We analyze the detection of $h'$ at the Large Hadron Collider (LHC) for a center-of-mass energy $\sqrt{s}=14~\text{TeV}$ and integrated luminosity $L_{\text{int}}=300~{\text{fb}}^{-1}$ via di-Higgs channel: $h'\to hh\to b\bar{b}\gamma\gamma$ and also in the $ZZ$ channel: $h'\to ZZ\to 4\ell~(\ell=e,~\mu)$ at an integrated luminosity $L_{\text{int}}=3000~{\text{fb}}^{-1}$. We consider three benchmark points for this analysis with $m_{h'}=250~\text{GeV},~400~\text{GeV}$, and $600~\text{GeV}$. We show that promising signals with good statistical significances can be obtained in di-Higgs channel, with $2\gamma+2b$-jets final states.

hep-ph↗
arXiv2020

Bound States of Right-handed Sneutrino Dark Matter

The relic abundance of the lightest right-handed sneutrino dark matter in supersymmetric B-L extension of the standard model is revisited. We argue that it can form a bound state through the exchange of light B-L Higgs boson and a large non-perturbative Sommerfeld effect is obtained. We emphasized that with this effect the relic abundance of right-handed sneutrino will lie within the observational limits and the right-handed sneutrino will remain a viable dark matter candidate of mass order up to 1.5 TeV.

hep-ph↗
arXiv2019

Dark Matter Spin Characterisation in Mono-$Z$ Channels

The $B-L$ Supersymmetric Standard Model (BLSSM) is an ideal testing ground of the spin nature of Dark Matter (DM) as it offers amongst its candidates both a spin-1/2 (the lightest neutralino) and spin-0 (the lightest right-handed sneutrino) state. We show that the mono-$Z$ channel can be used at the Large Hadron Collider (LHC) to diagnose whether a DM signal is characterised within the BLSSM by a fermionic or (pseudo)scalar DM particle. Sensitivity to either hypothesis can be obtained after only 100 fb$^{-1}$ of luminosity following Runs 2 and 3 of the LHC.

hep-ph↗
arXiv2018

Searching for Charged Higgs Bosons in the $B-L$ Supersymmetric Standard Model at the High Luminosity Large Hadron Collider

Upon assuming the $B-L$ Supersymmetric Standard Model (BLSSM) as theoretical framework accommodating a multi-Higgs sector, we assess the scope of the High Luminosity Large Hadron Collider (HL-LHC) in accessing charged Higgs bosons ($H^\pm$) produced in pairs from $Z'$ decays. We show that, by pursuing both di-jet and tau-neutrino decays, several signals can be established for $H^\pm$ masses ranging from about $M_{W}$ to above $m_t$ and $Z'$ masses between 2.5 TeV and 3.5 TeV. The discovery can be attained, even in a background free environment in some cases, owing to the fact that the very massive resonating $Z'$ ejects the charged Higgs bosons at very high transverse momentum, a kinematic region where any SM noise is hugely depleted.

hep-ph↗
arXiv2018

Long-Lived BLSSM Particles at the LHC

We investigate the collider signatures of neutral and charged Long-Lived Particles (LLPs), predicted by the Supersymmetric $B-L$ extension of the Standard Model (BLSSM), at the Large Hadron Collider (LHC). The BLSSM is a natural extension of the Minimal Supersymmetric Standard Model (MSSM) that can account for non-vanishing neutrino masses. We show that the lightest right-handed sneutrino can be the Lightest Supersymmetric Particle (LSP), while the Next-to-the LSP (NLSP) is either the lightest left-handed sneutrino or the left-handed stau, which are natural candidates for the LLPs. We analyze the displaced vertex signature of the neutral LLP (the lightest left-handed sneutrino), and the charged tracks associated with the charged LLP (the left-handed stau). We show that the production cross sections of our neutral and charged LLPs are relatively large, namely of order ${\cal O}(1)~{\rm fb}$. Thus, probing these particles at the LHC is quite plausible. In addition, we find that the displaced di-lepton associated with the lightest left-handed sneutrino has a large impact parameter that discriminates it from other SM leptons. We also emphasize that the charged track associated with the left-handed stau has a large momentum with slow moving charged tracks, hence it is distinguished from the SM background and therefore it can be accessible at the LHC.

hep-ph↗
arXiv2017

Dark Matter in B-L Supersymmetric Standard Model with Inverse Seesaw

We show that the $B-L$ Supersymmetric Standard Model with Inverse Seesaw (BLSSMIS) provides new Dark Matter (DM) candidates (lightest right-handed sneutrino and lightest $B-L$ neutralino) with mass of order few hundreds GeV, while most of other SUSY spectrum can be quite heavy, consistently with the current Large Hadron Collider (LHC) constraints. We emphasize that the thermal relic abundance and direct detection experiments via relic neutralino scattering with nuclei impose stringent constraints on the $B-L$ neutralinos. These constraints can be satisfied by few points in the parameter space where the $B-L$ lightest neutralino is higgsino-like, which cannot explain the observed Galactic Center (GC) gamma-ray excess measured by Fermi-LAT. The lightest right-handed sneutrino DM is analysed. We show that for a wide region of parameter space the lightest right-handed sneutrino, with mass between 80 GeV and 1.2 TeV, can satisfy the limits of the relic abundance and the scattering cross with nuclei. We also show that the lightest right-handed sneutrino with mass ${\cal O}(100)$ GeV can account for the observed GC gamma-ray results.

hep-ph↗
arXiv2016

Search for Mono-Higgs Signals at the LHC in the B-L Supersymmetric Standard Model

We study mono-Higgs signatures emerging in the $B-L$ supersymmetric standard model induced by new channels not present in the minimal supersymmetric standard model, i.e., via topologies in which the mediator is either a heavy $Z'$, with mass of ${\cal O}(2~{\rm TeV})$, or an intermediate $h'$ (the lightest CP-even Higgs state of $B-L$ origin), with mass of ${\cal O}(0.2~{\rm TeV})$. The mono-Higgs probe considered is the SM-like Higgs state recently discovered at the large hadron collider, so as to enforce its mass reconstruction for background reduction purposes. With this in mind, its two cleanest signatures are selected: $γγ$ and $ZZ^*\to 4l$ ($l=e,~μ$). We show how both of these can be accessed with foreseen energy and luminosity options using a dedicated kinematic analysis performed in presence of partonic, showering, hadronisation and detector effects.

hep-ph↗
arXiv2016

LHC signals of a BLSSM CP-even Higgs boson

We study the scope of the Large Hadron Collider in accessing a neutral Higgs boson of the $B-L$ Supersymmetric Standard Model. After assessing the surviving parameter space configurations following the Run 1 data taking, we investigate the possibilities of detecting this object during Run 2. For the model configurations in which the mixing between such a state and the discovered Standard Model-like Higgs boson is non-negligible, there exist several channels enabling its discovery over a mass range spanning from $\approx 140$ to $\approx$ 500 GeV. For a lighter Higgs state, with mass of order 140 GeV, three channels are accessible: $γγ$, $Zγ$ and $ZZ$, wherein the $Z$ boson decays leptonically. For a heavier Higgs state, with mass above 250 GeV (i.e., twice the mass of the Higgs state discovered in 2012), the hallmark signature is its decay in two such 125 GeV scalars, $h'\to hh$, where $hh\to b\bar b γγ$. In all such cases, significances above discovery can occur for already planned luminosities at the CERN machine.

hep-ph↗
arXiv2016

Alleviating the $\bar B \to D \tau \nu$ and $\bar B \to D^* \tau \nu_\tau$ puzzle in the MSSM

We show that Supersymmetric effects driven by penguin contributions to the $b \to c \tau \nu_\tau$ transition are able to account simultaneously for a sizeable increase of both branching ratios of $\bar{B}\to D \tau\bar{\nu}_{\tau}$ and $\bar{B} \to D^{*} \tau\bar{\nu}_{\tau}$ with respect to the Standard Model predictions, thereby approaching their experimentally measured values. We emphasise that a light chargino and neutralino, with masses less than 300 GeV, in addition to a large stau/snueutrino mass and a large $\tan\beta$, are essential for enhancing the effect of the lepton penguin $\tau \nu_\tau W^{\pm}$, which is responsible for the improved theoretical predictions with respect to current data.

hep-ph↗
arXiv2015

A viable logarithmic f(R) model for inflation

Inflation in the framework of $f(R)$ modified gravity is revisited. We study the conditions that $f(R)$ should satisfy in order to lead to a viable inflationary model in the original form and in the Einstein frame. Based on these criteria we propose a new logarithmic model as a potential candidate for $f(R)$ theories aiming to describe inflation consistent with observations from \textit{Planck} satellite (2015). The model predicts scalar spectral index $0.9615<n_s<0.9693$ in agreement with observation and tensor-to-scalar ratio $r$ of order $10^{-3}$. Furthermore, we show that for a class of models, a natural coupling between inflation and a scalar boson is generated through the minimal coupling between gravity and matter fields and a reheating temperature less that $10^9$ GeV is obtained.

hep-th↗
arXiv2015

Mono-jet, -photon and -Z Signals of a Supersymmetric (B-L) model at the Large Hadron Collider

Search for invisible final states produced at the Large Hadron Collider (LHC) by new physics scenarios are normally carried out resorting to a variety of probes emerging from the initial state, in the form of single-jet, -photon and -$Z$ boson signatures. These are particularly effective for models of Supersymmetry (SUSY) in presence of $R$-parity conservation, owing to the presence in their spectra of a stable neutralino as dark matter candidate. We assume here as theoretical framework Supersymmetric ($B-L$) extension of the Standard Model (BLSSM), wherein a mediator for invisible decays can be $Z'$ boson. The peculiarity of the signal is thus that the final state objects carry a very large (transverse) missing energy, since the $Z'$ is naturally massive and constrained by direct searches and electro-weak precision tests to be at least in TeV scale region. Under these circumstances the efficiency in accessing the invisible final state and rejecting the standard model background is very high. This somehow compensates the rather meagre production rates. Another special feature of this invisible BLSSM signal is its composition, which is often dominated by sneutrino decays (alongside the more traditional neutrino and neutralino modes). Sensitivity of the CERN machine to these two features can therefore help disentangling the BLSSM from more popular SUSY models. We assess in this analysis the scope of the LHC in establishing the aforementioned invisible signals through a sophisticated signal-to-background simulation carried out in presence of parton shower, hadronisation and detector effects. We find that significant sensitivity exists already after 300 fb$^{-1}$ during Run 2. We find that mono-jet events can be readily accessible at the LHC, so as to enable one to claim a prompt discovery, while mono-photon and -$Z$ signals can be used as diagnostic tools of the underlying scenario.

hep-ph↗