arXiv subjects

Mukesh Kumar

Publications and source records attributed to Mukesh Kumar.

At least 73 records · Page 4Linked to original sources

arXiv2016

Minimal Spin-3/2 Dark Matter in a simple $s$-channel model

We consider a spin~-~3/2 fermionic dark matter candidate (DM) interacting with Standard Model fermions through a vector mediator in the $s$-channel. We find that for pure vector couplings almost the entire parameter space of the DM and mediator mass consistent with the observed relic density is ruled out by the direct detection observations through DM-nucleon elastic scattering cross-sections. In contrast, for pure axial-vector coupling, the most stringent constraints are obtained from mono-jet searches at the Large Hadron Collider.

hep-ph↗

arXiv2016

Probing anomalous couplings using di-Higgs production in electron-proton collisions

A proposed high energy Future Circular Hadron-Electron Collider would provide sufficient energy in a clean environment to probe di-Higgs production. Using this channel we show that the azimuthal angle correlation between the missing transverse energy and the forward jet is a very good probe for the non-standard $hhh$ and $hhWW$ couplings. We give the exclusion limits on these couplings as a function of integrated luminosity at a $95$\% C.L. using the fiducial cross sections. With appropriate error fitting methodology we find that the Higgs boson self coupling could be measured to be $g^{(1)}_{hhh} = 1.00^{+0.24(0.14)}_{-0.17(0.12)}$ of its expected Standard Model value at $\sqrt s = 3.5(5.0)$ TeV for an ultimate 10 ab$^{-1}$ of integrated luminosity.

hep-ph↗

arXiv2016

Fermionic Dark Matter in a simple $t$-channel model

We consider a fermionic dark matter (DM) particle in renormalizable Standard Model (SM) gauge interactions in a simple $t$-channel model. The DM particle interactions with SM fermions is through the exchange of scalar and vector mediators which carry colour or lepton number. In the case of coloured mediators considered in this study, we find that if the DM is thermally produced and accounts for the observed relic density almost the entire parameter space is ruled out by the direct detection observations. The bounds from the monojet plus missing energy searches at the Large Hadron Collider are less stringent in this case. In contrast for the case of Majorana DM, we obtain strong bounds from the monojet searches which rule out DM particles of mass less than about a few hundred GeV for both the scalar and vector mediators.

hep-ph↗

arXiv2016

Differential cross section for the Higgs boson production in 4-lepton channel and $k_T$-factorization

We present our study of the differential cross section for the Higgs boson production in $k_T$-factorization framework. The $k_T$-factorization formalism includes a convolution over unintegrated parton distribution functions (uPDF) and off-shell parton level matrix element. The off-shell matrix element calculated considering initial gluons to be off-shell. We have considered only gluon fusion process which is dominant production mechanism for the Higgs boson production at LHC. We have used Ciafaloni-Catani-Fiorani-Marchesini (CCFM) uPDF based on CCFM evolution equations. We have compared our results with fixed order estimates up to NNLO+NNLL obtained using HRes tool within collinear factorization framework as well as with the ATLAS and CMS measurements of the corresponding differential distributions. This study will play an important role in understanding differential cross section within $k_T$-factorization framework.

hep-ph↗

arXiv2016

Phenomenological signatures of additional scalar bosons at the LHC

We investigate the search prospects for new scalars beyond the Standard Model (SM) at the Large Hadron Collider (LHC). In these studies two real scalars $S$ and $χ$ have been introduced in a two Higgs doublet model (2HDM), where $S$ is a portal to dark matter (DM) through its interaction with $χ$, a DM candidate and a possible source of missing transverse energy (\MET). Previous studies focused on a heavy scalar $H$ decay mode $H \to hχχ$, which was studied using an effective theory in order to explain a distortion in the Higgs ($h$) transverse momentum spectrum [16]. In this work, the effective decay is understood more deeply by including a mediator $S$, and the focus is changed to $H \to h S,~SS$ with $S \to χχ$. Phenomenological signatures of all the new scalars in the proposed 2HDM are discussed in the energy regime of the LHC, and their mass bounds have been set accordingly. Additionally, we have performed several analyses with final states including leptons and \MET, with $H \to 4 W$, $t\bar t H \to 6 W$ and $A \to ZH$ channels, in order to understand the impact these scalars have on current searches.

hep-ph↗

arXiv2016

Phenomenology of additional scalar bosons at the LHC

The confirmation of the Higgs boson in Run I data at the Large Hadron Collider (LHC) and the excesses in recent Run II data suggest scenarios beyond the Standard Model (SM). We pursue a study in a minimal model which is an extension of a scalar doublet in the SM known as two-Higgs doublet model (THDM). Following earlier suggestions two real scalars $χ$ and $S$ have been introduced in the THDM where $χ$ is treated as a candidate for dark matter. $χ$ does not receive any vacuum expectation value ($vev$) in the model whereas the Higgs-like scalar $S$ acquires $vev$. This allows small mixing between the $CP$-even scalars of the THDM, $h$, $H$ and $S$. In this study the mass spectrum of new scalars is taken to be $2 m_h < m_H < 2 m_t$, $m_χ< m_h/2$, $m_h \lesssim m_S \lesssim m_H - m_h$, $m_A > 2 m_t$ and $m_H^\pm < m_A$, where $m_h$ and $m_t$ is masses of the SM Higgs and top-quark respectively, $m_H, m_A$ and $m_{H^\pm}$ are the masses of the heavy $CP$-even scalar $H$, $CP$-odd scalar $A$, and charged Higgs $H^\pm$, respectively. A partial list of potential search channels at the LHC has been provided with possible phenomenological consequences. The expected phenomenology and constraints on parameters are also discussed in a model-independent approach .

hep-ph↗

arXiv2016

The impact of additional scalar bosons at the LHC

In this study we consider an effective model by introducing two hypothetical real scalars, $H$ and $χ$ - a dark matter candidate, where the masses of these scalars are $2 m_h < m_H < 2 m_t$ and $m_χ\approx m_h/2$ with $m_h$ and $m_t$ being the Standard Model Higgs boson and top quark masses respectively. A distortion in the transverse momentum distributions of $h$ in the intermediate region of the spectrum through the processes $p p \to H \to hχχ$ could be observed in this model. An additional scalar, $S$, has been postulated to explain large $H \to hχχ$ branching ratios, assuming $m_h \lesssim m_S \lesssim m_H-m_h$ and $m_S > 2 m_χ$. Furthermore, a scenario of a two Higgs doublet model (2HDM) is introduced and a detailed proposal at the present energies of the Large Hadron Collider to study the extra CP-even ($h, H$), CP-odd ($A$) and charged ($H^\pm$) scalars has been pursued. With possible phenomenological implications, all possible spectra and decay modes for these scalars are discussed. Based on the mass spectrum of $H, A$ and $H^\pm$, the production of multi-leptons and $Z$+jets+missing-energy events are predicted. A specific, Type-II 2HDM model is discussed in detail.

hep-ph↗

arXiv2015

Examining the performance of refractory conductive ceramics as plasmonic materials: a theoretical approach

The main aim of this study is to scrutinize promising plasmonic materials by understanding their electronic structure and correlating them to the optical properties of selected refractory materials. For this purpose, the electronic and optical properties of the conductive ceramics TiC, ZrC, HfC, TaC, WC, TiN, ZrN, HfN, TaN, and WN are studied systematically by means of first-principles density functional theory. A full ab initio procedure to calculate plasma frequency from the electronic band structure is discussed. The dielectric functions are calculated by including electronic interband and intraband transitions. Our calculations confirm that transition metal nitrides, such as TiN, ZrN, and HfN, are the strongest candidates, exhibiting performance comparable to that of conventional noble metals in the visible to the near-infrared regions. On the other hand, carbides are not suitable for plasmonic applications because they show very large losses in the same regions. From our calculated dielectric functions, the scattering and absorption efficiencies of nanoparticles made of these refractory materials are evaluated. It is revealed that TiN and TaC are the best candidate materials for applications in photothermal energy conversion over a broad spectral region. Furthermore, quality factors for localized surface plasmon resonance and surface plasmon polaritons are calculated to compare quantitative performances, and ZrN and HfN are found to be comparable to conventional plasmonic metals such as silver and gold

physics.comp-ph↗

arXiv2015

Band engineering of ternary metal nitride system Ti1-x ZrxN for plasmonic applications

Chemical composition is the primary factor that determines the electronic band structure and thus also influences the optical properties of plasmonic ceramics including nitrides and oxides. In this work, the optical and plasmonic properties of TiN, ZrN and their hypothetical intermediate alloys Ti1-xZrxN (x= 0, 0.25, 0.50, 0.75, and 1), are studied by using first-principles density functional theory. We demonstrate the effects of electronic band structure tuning (band engineering) on the dielectric properties by varying the concentration of metallic constituents. Our calculations reveal that bulk plasma frequency, onset of interband transitions, width of bulk plasmon resonance and cross-over frequency, can be tuned flexibly in visible spectrum region by varying the amount of Zr concentration in Ti1-xZrxN alloy system. We found that low threshold interband energy onset (~1.95 eV) leads to high losses in Ti rich compounds than that of ZrN which points to lower losses.

physics.comp-ph↗

arXiv2015

The compatibility of LHC Run 1 data with a heavy scalar of mass around 270\,GeV

The first run of the LHC was successful in that it saw the discovery of the elusive Higgs boson, a particle that is consistent with the SM hypothesis. There are a number of excesses in Run 1 ATLAS and CMS results which can be interpreted as being due to the existence of another heavier scalar particle. This particle has decay modes which we have studied using LHC Run 1 data. Using a minimalistic model, we can predict the kinematics of these final states and compare the prediction against data directly. A statistical combination of these results shows that a best fit point is found for a heavy scalar having a mass of 272$^{+12}_{-9}$\,GeV. This result has been quantified as a three sigma effect, based on analyses which are not necessarily optimized for the search of a heavy scalar. The smoking guns for the discovery of this new heavy scalar and the prospects for Run 2 are discussed.

hep-ph↗

arXiv2015

Measuring anomalous $Wtb$ couplings at $e^-p$ collider

We study the accuracy with which the lowest order $CP$ conserving anomalous $Wtb$ couplings in the single top quark production at the proposed large hadron electron collider (LHeC) can be probed. The one dimensional distribution of various kinematic observables at the parton level MC and their asymmetries arising due to the presence of anomalous couplings both in the hadronic and leptonic $W$ decay is examined. \par We find that at 95 \% C.L. the anomalous coupling associated with the left handed vector current can be measured at an accuracy of the order of $\sim 10^{-2}-10^{-3}$, while those associated with the right handed vector and left as well as right handed tensor currents have sensitivity at the order of $\sim 10^{-1}-10^{-2}$ for the systematic uncertainty varying between 10\%-1\% at an integrated luminosity of 100 fb$^{-1}$. A comprehensive analysis of the combined covariance matrix derived from all one dimensional distributions of kinematical observables is used to compute the errors in anomalous couplings.

hep-ph↗

arXiv2015

High order parameter-robust numerical method for a system of (M>=2) coupled singularly perturbed parabolic reaction-diffusion problems

We present a high order parameter-robust numerical method for a system of (M>=2) coupled singularly perturbed parabolic reaction-diffusion problems. A small perturbation parameter ε is multiplied with the second order spatial derivatives in all the equations. The parabolic boundary layer appears in the solution of the problem when the perturbation parameter ε tends to zero. To obtain a high order approximation to the solution of this problem, we propose a numerical method that employs the Crank-Nicolson method on an uniform mesh in time direction, together with a hybrid finite difference scheme on a generalized Shishkin mesh in spatial direction. We prove that the resulting method is parameter-robust or ε-uniform of second order in time and almost fourth order in spatial variable, if the discretization parameters satisfy a non-restrictive relation. Numerical experiments are presented to validate the theoretical results and also indicate that the relation between the discretization parameters is not necessary in practice.

math.NA↗

arXiv2015

Single Top and Higgs Production in $e^- p$ collisions

In this proceedings some studies on the prospects of single top production at the Large Hadron Electron Collider (LHeC) and double Higgs production at the Future Circular Hadron Electron Collider (FCC-he) shall be presented. In particular, we investigated the $tbW$ couplings via single top quark production with the introduction of possible anomalous Lorentz structures, and measured the sensitivity of the Higgs self coupling ($λ$) through double Higgs production. The studies are performed with 60 GeV electrons colliding with 7 (50) TeV protons for the LHeC (FCC-he). For the single top studies a parton level study has been performed, and we find the sensitivity of the anomalous coupling at a 95\% C.L, considering 10-1\% systematic errors. The double Higgs production has been studied with speculated detector parameters and the sensitivity of $λ$ estimated via the cross section study around the Standard Model Higgs self coupling strength ($λ_{SM}$) considering 5\% systematic error in signal and backgrounds. Effects of non-standard CP-even and CP-odd couplings for $hhh$, $hWW$ and $hhWW$ vertices have been studied and constrained at 95\% C.L.

hep-ph↗

arXiv2014

Probing the Higgs Boson via VBF with Single Jet Tagging at the LHC

The signature produced by the Standard Model Higgs boson in the Vector Boson Fusion (VBF) mechanism is usually pinpointed by requiring two well separated hadronic jets, one of which (at least) of them tends to be in the forward direction. With the increase of instantaneous luminosity at the LHC, the isolation of the Higgs boson produced with the VBF mechanism is rendered more challenging. In this paper the feasibility of single jet tagging is explored in a high-luminosity scenario. It is demonstrated that the separation in rapidity between the tagging jet and the Higgs boson can be effectively used to isolate the VBF signal. This variable is robust from the experimental and QCD stand points. Single jet tagging allows us to probe the spin-CP quantum numbers of the Higgs boson.

hep-ph↗

arXiv2013

Improved Family of Estimators of Population Mean in Simple Random Sampling

In this paper, a procedure is given for estimating the population mean in simple random sampling without replacement in the presence of auxiliary information. The mean squared error expressions of the proposed estimators have been derived under large sample approximation. We have compared the performances of the proposed estimators with several existing estimators. Both theoretical and empirical findings are encouraging and support the soundness of the proposed procedure for mean estimation.

math.ST↗

arXiv2013

Top quark physics in the Vector Color-Octet Model

We study and constrain the parameter space of the vector color-octet model from observed data at Tevatron by studying top quark pair production and associated observables afbt and spin-correlation. In particular we study invariant mass and rapidity dependence of afbt at Tevatron. In addition to FC couplings we extend our study to include FV coupling involving first & third generation quarks for both these processes. In order to ensure that we remain within the constraints imposed by LHC data, we analyze the charge asymmetry, p_T spectrum & invariant mass in t\bar t production data at LHC. The constraints from dijet resonance searches performed by LHC are also considered. We also explore the contribution of this model to single top quark production mediated by charged & neutral color-octet vector bosons. FV couplings introduced then induce same-sign top-pair production process which is analyzed for both hadron colliders. We have incorporated effect of finite decay width of color octets on these processes. We find that it is possible to explain the observed afbt anomaly in color-octet vector model without transgressing production cross sections of all these processes both through FC and FV couplings at Tevatron. We predict best point sets in model parameter space for specific choices of color-octet masses corresponding to chi^2_min evaluated using mttb and dyy spectrum of afbt from observed data set at Tevatron (8.7 fb-1). We find that single top quark production is more sensitive to FC and FV couplings in comparison to top-pair production. We provide 95% exclusion contours on the plane of FV chiral couplings from recent data at Tevatron, CMS and ATLAS corresponding to nonobservability of large same-sign dilepton events. The four observed point sets are consistent with the cross section, charge asymmetry and spin-correlation measurements for t\bar t production & dijet searches at LHC.

hep-ph↗

arXiv2013

A general family of dual to ratio-cum-product estimator in sample surveys

This paper presents a family of dual to ratio-cum-product estimators for the finite population mean. Under simple random sampling without replacement (SRSWOR) scheme, expressions of the bias and mean-squared error (MSE) up to the first order of approximation are derived. We show that the proposed family is more efficient than usual unbiased estimator, ratio estimator, product estimator, Singh estimator (1967), Srivenkataramana (1980) and Bandyopadhyaya estimator (1980) and Singh et.al. (2005) estimator. An empirical study is carried out to illustrate the performance of the constructed estimator over others.

stat.ME↗

arXiv2013

Dual To Ratio Cum Product Estimator In Stratified Random Sampling

Tracy et al.[8] have introduced a family of estimators using Srivenkataramana and Tracy ([6],[7]) transformation in simple random sampling. In this article, we have proposed a dual to ratio-cum-product estimator in stratified random sampling. The expressions of the mean square error of the proposed estimators are derived. Also, the theoretical findings are supported by a numerical example.

stat.ME↗