arXiv subjects

Mukesh Kumar

Publications and source records attributed to Mukesh Kumar.

At least 37 records · Page 2Linked to original sources

arXiv2024

Trials Factor for Semi-Supervised NN Classifiers in Searches for Narrow Resonances at the LHC

To mitigate the model dependencies of searches for new narrow resonances at the Large Hadron Collider (LHC), semi-supervised Neural Networks (NNs) can be used. Unlike fully supervised classifiers these models introduce an additional look-elsewhere effect in the process of optimising thresholds on the response distribution. We perform a frequentist study to quantify this effect, in the form of a trials factor. As an example, we consider simulated $Zγ$ data to perform narrow resonance searches using semi-supervised NN classifiers. The results from this analysis provide substantiation that the look-elsewhere effect induced by the semi-supervised NN is under control.

hep-ph↗

arXiv2024

The scale invariant scotogenic model: CDF-II $W$-boson mass and the 95 GeV excesses

The anomalies observed in the $W$ mass measurements at the CDF-II experiments and the excesses seen around 95~GeV at the Large Hadron Collider (LHC) motivate this work, in which we investigate and constrain the parameter space of the Scale Invariant Scotogenic Model with a Majorana dark matter candidate. The scanned parameters are chosen to be consistent with the dark matter relic density and the observed excesses at $\sim95$~GeV signal strength rates in different channels. We found that significant part of the viable space addresses the excess in the channel $γγ$, while a tight part can address the excess in both $γγ$ and $b\bar{b}$ channels. Furthermore, the model's viable parameters can be probed in both the LHC and future $e^{+}e^{-}$ colliders for di-Higgs production.

hep-ph↗

arXiv2024

Axion-Like Particles at future $e^- p$ collider

In this work, we explore the possibilities of producing Axion-Like Particles (ALPs) in a future $e^-p$ collider. Specifically, we focus on the proposed Large Hadron electron collider (LHeC), which can achieve a center-of-mass energy of $\sqrt{s} \approx 1.3$~TeV, enabling us to probe relatively high ALP masses with $m_a \lesssim 300$~GeV. The production of ALPs can occur through various channels, including $W^+W^-$, $γγ$, $ZZ$, and $Zγ$-fusion within the collider environment. To investigate this, we conduct a comprehensive analysis that involves estimating the production cross section and constraining the limits on the associated couplings of ALPs, namely $g_{WW}$, $g_{γγ}$, $g_{ZZ}$, and $g_{Zγ}$. To achieve this, we utilize a multiple-bin $χ^2$ analysis on sensitive differential distributions. Through the analysis of these distributions, we determine upper bounds on the associated couplings within the mass range of 5~GeV $\leq m_a \leq$ 300~GeV. The obtained upper bounds are of the order of ${\cal O}(10^{-1})$ for $g_{γγ}$ ($g_{WW}$, $g_{ZZ}$, $g_{Zγ}$) in $m_a \in$~[5, 200 (300)]~GeV considering an integrated luminosity of 1~ab$^{-1}$. Furthermore, we compare the results of our study with those obtained from other available experiments. We emphasize the limits obtained through our analysis and showcase the potential of the LHeC in probing the properties of ALPs.

hep-ph↗

arXiv2023

Searches for Additional Scalars at Future $e^{+} e^{-}$ Colliders

We present growing excesses consistent with a 95 GeV scalar. We provide a comprehensive analysis of the Two Higgs Doublet Model and an additional singlet (2HDM+S) at future $e^{+} e^{-}$ collider. In particular, we provide a precise mass reconstruction measurement for the scalar, $m_{S}$, using the recoil mass method through $e^{+} e^{-} \to Z S$ where $Z \to μ_{+} μ_{-}$ and $S \to b \bar{b}$ at $\sqrt{s} = 250$~GeV and $\sqrt{s} = 200$~GeV. Furthermore, we employ Deep Neural Network to analyze the properties and behaviour of the scalar particle with a mass most importantly to provide enhanced resolution for the separation between beyond the Standard Model (SM) signal and SM background in the region 95 - 96 GeV in the $S \to b \bar{b}$ for $μ_{+} μ_{-}$ channel. A 95 GeV scalar can be observed with $5σ$ significance at $15(10)$ fb$^{-1}$ integrated luminosity for $\sqrt{s} = 250(200)$~GeV. This strengthens the discovery of the potential of the future $e^{+} e^{-}$ collider.

hep-ph↗

arXiv2023

Constraining 2HDM+S model through W-boson mass measurements

Following a discussion on $W$-boson mass observed at the CDF and ATLAS, we explore the parameter space allowed in the 2HDM+$S$ model. Further, the model parameter space is constrained through vector-like leptons via muon $g-2$ measurements. We show our results for additional scalar mass fixed to $m_S \approx 95$ and $150$~GeV keeping the standard Higgs-boson mass at 125~GeV in all four types of 2HDM+$S$ model. The chosen mass of the singlet scalar is motivated by the excesses seen at the CMS and ATLAS data in proton-proton collisions at the Large Hadron Collider.

hep-ph↗

arXiv2023

Accumulating Evidence for the Associated Production of a New Higgs Boson at the Large Hadron Collider

In the last decades, the Standard Model (SM) of particle physics has been extensively tested and confirmed, with the announced discovery of the Higgs boson in 2012 being the last missing puzzle piece. Even though since then the search for new particles and interactions has been further intensified, the experiments ATLAS and CMS at the Large Hadron Collider (LHC) at CERN did not find evidence for the direct production of a new state. However, in recent years deviations between LHC data and SM predictions in multiple observables involving two or more leptons (electrons or muons) have emerged, the so-called ``multi-lepton anomalies'', pointing towards the existence of a beyond the SM Higgs boson $S$. While from these measurements its mass cannot be exactly determined, it is estimated to lay in the range between $130\,$GeV and $160\,$GeV. Motivated by this observation, we perform a search for signatures of $S$, by using existing CMS and ATLAS analyses. Combining channels involving the associate productions of SM gauge bosons ($γγ$ and $Zγ$), we find that a simplified model with a new scalar with $m_S= 151.5\,$GeV is preferred over the SM hypothesis by 4.3$σ$ (3.9$σ$) locally (globally). On the face of it, this provides a good indication for the existence of a new scalar resonance $S$ decaying into photons, in association with missing energy and allows for a connection to the long-standing problem of Dark Matter. Furthermore, because $S$ is always produced together with other particles, we postulate the existence of a second new (heavier) Higgs boson $H$ that decays into $S$ and propose novel searches to discover this particle, which can be performed by ATLAS and CMS.

hep-ph↗

arXiv2023

Direct Determination of Photonic Stopband Topological Character: A Framework based on Dispersion Measurements

Ascertainment of photonic stopband absolute topological character requires information regarding the Bloch eigenfunction spatial distribution. Consequently, the experimental investigations predominantly restrict themselves to the bulk-boundary correspondence principle and the ensuing emergence of topological surface state. Although capable of establishing the equivalence or inequivalence of bandgaps, the determination of their absolute topological identity remains out of its purview. The alternate method of reflection phase-based identification also provides only contentious improvements owing to the measurement complexities pertaining to the interferometric setups. To circumvent these limitations, we resort to the Kramers-Kronig amplitude-phase causality considerations and propose an experimentally conducive method for bandgap topological character determination directly from the parametric reflectance measurements. Particularly, it has been demonstrated that in case of one-dimensional photonic crystals, polarization-resolved dispersion measurements suffice in qualitatively determining bandgap absolute topological identities. By invoking the translational invariance of the investigated samples, we also define a parameter Differential Effective Mass that encapsulates bandgap topological identities and engenders an experimentally discernible bandgap classifier.

physics.optics↗

arXiv2023

Growing Excesses of New Scalars at the Electroweak Scale

We combine searches for scalar resonances at the electroweak scale performed by the Large Hadron Collider experiments ATLAS and CMS where persisted excesses have been observed in recent years. Using both the side-bands of Standard Model Higgs analyses as well as dedicated beyond the Standard Model analyses, we find significant hints for new scalars at $\approx 95\,$GeV ($S^\prime$) and $\approx152\,$GeV ($S$). The presence of a $95\,$GeV scalar is preferred over the Standard Model hypothesis by $3.8σ$, while interpreting the $152\,$GeV excesses in a simplified model with resonant pair production of $S$ via a new heavier scalar $H(270)$, a global significance of $\approx5σ$ is obtained. While the production mechanism of the $S^\prime$ cannot yet be determined, data strongly favours the associated production of $S$, i.e. via the decay of a heavier boson $H$ ($pp\to H\to SS^*$). A possible alternative or complementary decay chain is $H\rightarrow SS^{\prime}$, where $S\to WW^*$ ($S^{\prime}$) would be the source of the leptons ($b$-quarks) necessary to explain the multi-lepton anomalies found in Large Hadron Collider data.

hep-ph↗

arXiv2023

Exploring dark $Z_d$-boson in future Large Hadron-electron collider

The interaction between the dark $U(1)_d$ sector with the visible Standard Model (SM) sector takes place through the kinetic mixing between the dark photon $U(1)_d$ field $Z_d^μ$ and the SM $U(1)_Y$ gauge field $B_μ$. After the electroweak and $U(1)_d$ symmetry breaking, the dark photon $Z_d^μ$ acquires a mass and mixes with the SM neutral vector boson $Z_μ$. This mixing leads to parity-violating coupling between the $Z_d^μ$ and SM. The coupling between the dark photon and SM can be explored in low energy phenomenology as well as in collider experiments. The Lorentz structure of dark photon interaction with SM fermions is explored in the proposed high energy future Large Hadron-electron collider, which would provide efficient energy and a clean environment using cross-section and asymmetries associated with polarisation observable of the dark photon in leptons decay. A $χ^2$-analysis is performed to compare the strength of various variables for both the charge- and neutral-current processes. Based on this analysis, $90\%$ confidence level (C.L.) contours in the $ε$-$m_{Z_d}$ and $ε$-$g_V$ plane are obtained to put limits on the $Z_d^μ$ mass up to $100$ GeV, coupling strength $ε$ and on the Lorentz structure of dark photon coupling with the SM fermions ($g_V$) at $\sqrt{s} \approx 1.3$ TeV.

hep-ph↗

arXiv2023

Feasibility of the observation of a heavy scalar through the fully hadronic final state at the LHeC

The proposed future Large Hadron Electron Collider provides sufficient center of mass energies, $\sqrt{s}$, to probe heavy particles decaying into $W^\pm(Z)-$boson of mass $>2m_W$ $(2m_Z)$. In this work we present a study to produce one such heavy $C P$ even scalar $H$ of mass $2m_h < m_H < 2 m_t$ through charged-current production mode where $H \to W^+W^-$, where hadronic decay of $W^\pm-$boson is considered to reconstruct $m_H$. Due to the presence of missing energy and forward jet in this channel, it is challenging to reconstruct $m_H$ with above final state and thus we employed three different reconstruction methods and discuss the significance of each one. For this analysis we consider a benchmark value of $m_H = 270$\,GeV and $\sqrt{s} \approx 1.3$\,TeV with an assumed luminosity of 1\,ab$^{-1}$.

hep-ph↗

arXiv2023

Connecting multi-lepton anomalies at the LHC and in Astrophysics with MeerKAT/SKA

Multi-lepton anomalies at the Large Hadron Collider (LHC) are reasonably well described by a two Higgs doublet model with an additional singlet scalar. Here, we demonstrate that using this model with parameters set by the LHC, we are also able to describe the excesses in gamma-ray flux from the galactic centre and the cosmic-ray spectra from AMS-02. This is achieved through Dark Matter (DM) annihilation via the singlet scalar. Of great interest is the flux of synchrotron emissions which results from annihilation of DM in Milky-Way satellites. We make predictions for MeerKAT/SKA observations of the nearby dwarf galaxy Reticulum II and we demonstrate the power of this instrument as a new frontier in indirect dark matter searches. Since the dark matter sector of the aforementioned two Higgs doublet model is unconstrained by current LHC data, we also demonstrate a synergy between particle and astrophysical searches in order to motivate further exploration of this promising model.

astro-ph.HE↗

arXiv2022

Neutrino specific spin-3/2 dark matter

In this paper we consider a spin-$\frac{3}{2}$ dark matter (DM) particle coupled to neutrinos as a viable candidate to produce the observed DM relic density through the thermal freeze-out mechanism. The couplings of DM to neutrinos is considered first in a most general dimension six effective field theory framework. We then consider two specific neutrino-portal models discussed in the literature. In the first model DM couples to the standard model neutrinos through mixing generated by a sterile pseudo-Dirac massive neutrino and the second model we consider is the widely studied $U(1)_{L_μ- L_τ}$ gauge symmetric model. For each of these models we explore the parameter space required to generate the observed relic density. The constraints on the parameters of these models from the existing and proposed neutrino experiments as well as from existing cosmological and astrophysical bounds are considered in the context of the relic density calculations.

hep-ph↗

arXiv2022

High-yield exfoliation of MoS2 nanosheets by a novel spray technique and the importance of soaking and surfactants

Liquid-phase exfoliation of two-dimensional materials is very attractive for large-scale applications. Although used extensively, isolating MoS2 layers (<10) with high efficiency is reported to be extremely difficult. Further, the importance of soaking has not yet been studied, and the surfactants' role in stabilizing MoS2 nanosheets is poorly understood1. Herein, we report a novel approach to exfoliating large quantities of MoS2 via high-pressure (HP) liquid-phase exfoliation (LPE) in deionized (DI) water. 4 to 7 layers of MoS2 nanosheets were obtained from 60 days-soaked samples and they were found to be stable in solvents for periods of up to six months. Studies on the effect of three surfactants, namely sodium dodecyl benzenesulfonate (SDBS), sodium cholate (SC), and tetra-butyl ammonium bromide (TBAB), indicate that exfoliation of MoS2 nanosheets in SDBS is highly efficient than the other two surfactants. The estimated yield reaches up to 7.25%, with a nanosheet concentration of 1.45 mg/ml, which is one of the highest ever reported. Our studies also suggest that the nanosheets' concentration and the lateral size depend on exfoliation cycles, applied pressure and surfactant concentration. Hydrogen evolution reaction (HER) and ion-transport study show that the nanosheets prepared by our method are stable in an acidic medium and free from surfactants. A high hydrogen evolution rate of 30.13 mmol g-1 h-1 was estimated under ambient laboratory conditions.

cond-mat.mes-hall↗

arXiv2022

Measuring $CP$ nature of $hτ{\barτ}$ coupling at $e^-p$ collider

The proposed future $e^- p$ collider provides sufficient energies to produce the Standard Model Higgs Boson ($h$) through $W^\pm$ and $Z$-Boson fusion in charged and neutral current modes, respectively and to measure its properties. We take this opportunity to investigate the prospect of measuring the $CP$ properties of $h$ through $h \to τ^+ τ^-$, where $τ^-\,\left(τ^+\right)$ decays to a charged pion $π^-\,\left(π^+\right)$ and a neutral pion $π^0$ in association with neutrino (anti-neutrino). An interesting $CP$ sensitive angular observable $α_{\rm CP}$ between the two $τ$-leptons decay plane in the $π^+π^-$ centre of mass frame is proposed and investigated in this work. For fixed electron energy of 150 GeV along with 7 (50) TeV of proton energy, the $CP$ phase can be measured approximately to $25^\circ$ ($14^\circ$) at integrated luminosity of 1~ab$^{-1}$ for $-$80\% polarised electron at 95\% confidence level.

hep-ph↗

arXiv2021

On-chip Nanophotonic Broadband Wavelength Detector with 2D-Electron Gas

Miniaturized, low-cost wavelength detectors are gaining enormous interest as we step into the new age of photonics. Incompatibility with integrated circuits or complex fabrication requirement in most of the conventionally used filters necessitates the development of a simple, on-chip platform for easy-to-use wavelength detection system. Also, intensity fluctuations hinder precise, noise free detection of spectral information. Here we propose a novel approach of utilizing wavelength sensitive photocurrent across semiconductor heterojunctions to experimentally validate broadband wavelength detection on an on-chip platform with simple fabrication process. The proposed device utilizes linear frequency response of internal photoemission via 2-D electron gas in a ZnO based heterojunction along with a reference junction for coherent common mode rejection. We report sensitivity of 0.96 uA/nm for a broad wavelength-range of 280 nm from 660-940 nm. Simple fabrication process, efficient intensity noise cancelation along with heat resistance and radiation hardness of ZnO makes the proposed platform simple, low-cost and efficient alternative for several applications such as optical spectrometers, sensing and IOTs.

physics.optics↗

arXiv2021

Understanding two same-sign and three leptons with $b$-jets in four top quark events at the LHC

The top quark is the heaviest known elementary particle of the Standard Model (SM) of particle physics and, therefore, it is expected to have large couplings to hypothetical new physics in many models beyond the SM (BSM). Various studies have predicted the presence of multi-lepton anomalies at the LHC. One of those anomalies is the excess production of two same-sign leptons and three isolated leptons in association with $b$-jets. These are reasonably well described by a 2HDM+$S$ model, where $S$ is a singlet scalar. Both the ATLAS and CMS experiments have reported sustained excesses in these final states. This includes corners of the phase-space where production of top quark pairs in association with a $W$ boson contributes to. Here, we investigate the production of two same-sign and three leptons from the production of four top quark final states. Our focus is on understanding the differences between the SM and BSM production mechanisms of four top quarks from $t\overline{t} A$ ($A \rightarrow t\overline{t}$) using Machine Leaning techniques with twelve discriminating kinematic variables.

hep-ph↗

arXiv2021

The anomalous production of multi-lepton and its impact on the measurement of $Wh$ production at the LHC

Anomalies in multi-lepton final states at the Large Hadron Collider (LHC) have been reported in Refs.~\cite{vonBuddenbrock:2017gvy,vonBuddenbrock:2019ajh}. These can be interpreted in terms of the production of a heavy boson, $H$, decaying into a Standard Model (SM) Higgs boson, $h$, and a singlet scalar, $S$, which is treated as a SM Higgs-like boson. This process would naturally affect the measurement of the $Wh$ signal strength at the LHC, where $h$ is produced in association with leptons and di-jets. Here, $h$ would be produced with lower transverse momentum, $p_{Th}$, compared to SM processes. Corners of the phase-space are fixed according to the model parameters derived in Refs.~\cite{vonBuddenbrock:2016rmr,vonBuddenbrock:2017gvy} without additional tuning, thus nullifying potential look-else-where effects or selection biases. Provided that no stringent requirements are made on $p_{Th}$ or related observables, the signal strength of $Wh$ is $μ(Wh)=2.41 \pm 0.37$. This corresponds to a deviation from the SM of $3.8σ$. This result further strengthens the need to measure with precision the SM Higgs boson couplings in $e^+e^-$, and $e^-p$ collisions, in addition to $pp$ collisions.

hep-ph↗

arXiv2020

Transitioning Universe with hybrid scalar field in Bianchi I space-time

In this paper we investigate a Bianchi type I transitioning Universe in Brans-Dicke theory. To get an explicit solution of the field equations, we assume scalar field as $ϕ= ϕ_{0}\left[t^αexp(βt)\right]^δ$ with $ϕ_{0}$, $α$, $β$ and $δ$ as constants. The values of $α$ and $β$ are obtained by probing the proposed model with recent observational Hubble data (OHD) points. The interacting and non-interacting scenarios between dark matter and dark energy of the derived Universe within the framework of Brans-Dicke gravity are investigated. The $om(z)$ analysis of the Universe in derived model shows that the Universe is filled with dynamical dark energy with its equation of state parameter $ω_{de} > -1$. Hence the Universe behaves like a quintessence model at present epoch. Some physical properties of the Universe are also discussed.

gr-qc↗