arXiv subjects

Siba Prasad Das

Publications and source records attributed to Siba Prasad Das.

At least 19 recordsLinked to original sources

arXiv2026

Thermodynamic properties of the Kerr Black-hole in non-linear electrodynamics with cosmological constant

We study thermodynamic properties, in particular the Temperature~(T), Angular velocity~($Ω_h$) and Entropy~(S) of the of magnetically charged slowly rotating (with rotation parameter $a \lsim 0.10$) Kerr black-hole(BH) with the inclusion of cosmological constant ($Λ$) in the background of nonlinear electrodynamics (NLED). At first we calculated the nonlinear electromagnetic magnetic charged density $ρ_{NLED}$$(r)$ which is needed to calculate the magnetic mass of the slowly rotating Kerr-BH. We showed the mass profile $M(r)$ of the BH for different combinations of magnetic charges~($q_m$) and non-linear parameter ($β$) presence in the Lagrangian density. We found that $M(r)$ attains a plateau for values of $r$ close to the the cosmological length~($L$), where $L^2$= $\pm \fracΛ{3}$, irrespective of the combinations of $q_m$ and $β$. The $\pm$ sign corresponds to the de-Sitter(dS) and Anti-de-Sitter(AdS) respectively. Afterwards we showed the allowed parameter spaces in $a$-$M$ plane using sharkfin diagram for different values of $L$ with positive values of the horizon function, $Δ(r)$, and explain the extremal criterion and asymptotic limit. We showed the values of $r$ where the horizon function of the quadratic polynomials becomes zero and called them as the inner(Cauchy), outer(Event) and large cosmological horizons with different values of $a$. We showed that the horizon structure depends on $a$, $L$ and the mass profile $M(r)$. Finally, we tabulated the numerical values of three thermodynamic parameter, i.e., $T$, $Ω_h$ and $S$ at those horizons surfaces. Our results demonstrate that NLED with cosmological constant significantly modifies both the internal structure and thermodynamic properties of Kerr-BH.

gr-qc↗

arXiv2026

Lepton asymmetry leading to baryogenesis by primordial black holes

Baryogenesis remains an unresolved problem in cosmology, with existing mechanisms facing significant caveats. We show that the effects of primordial black holes (PBHs) on neutrinos produce the lepton asymmetry $\sim 10^{-10}$ which subsequently produces the baryon asymmetry. We consider the Dirac Lagrangian in curved spacetime in local coordinates exhibiting Hermitian pseudo-vector and non-Hermitian vector terms. These terms lead to energy splitting between weakly interacting neutrinos and antineutrinos, resulting in their unequal number densities and hence a lepton asymmetry. While the non-Hermitian effect leads to a non-conserved total probability of neutrinos, the leptogenesis due to gravitational effects of a PBH could be significant until the nucleosynthesis era. This in turn produces baryon asymmetry from the symmetry of lepton and baryon numbers via the sphaleron process in the electro-weak era. We show that in the most conservative scenario, the PBHs of mass $\sim 10^{12}$ g and spin $\sim 0.01$ produce the observed baryogenesis at temperature 130 GeV, when such PBHs are available abundantly. However, massive PBHs also could produce the observed asymmetry, assuming the non/anti-Hermitian vector couplings for neutrino and anti-neutrino get canceled from the Lagrangian, leading the system to be Hermitian.

hep-ph↗

arXiv2024

A short introduction on Angular momentum of Kerr Blackhole

General relativity (GR) predicts the existence of black hole (BH). The rotating BH called as a Kerr Black hole and GR implies that there is an upper limit on the angular momentum per mass squared of black holes $\leq 1$, above which the event horizon of the Kerr BH is not exist. We find the radial equation for equatorial motion for Kerr BH in terms of the effective potential. We have shown the effective potential profile for different rotation parameter ($a$). We find the solution of the radial equation of the Kerr metric and found the expression of the angular momentum per unit mass squared, $\tilde a = \frac{a}{M}$. We showed the profile of $\tilde a$ as a function of $\frac{r}{M}$. The solution also leads the energy per unit rest mass ($e$) and we showed its behavior as a function of $\frac{r}{M}$. We enumerated the maximum values of radius of innermost stable circular orbit ($r_{ISCO}$) for $\tilde a=1$.

gr-qc↗

arXiv2018

Neutral and Charged Higgs boson phenomenology at the LHeC and FCC-eh

We have analyzed the prospects of observing the lightest CP-even neutral Higgs boson ($h_1$) via decays into $b \bar b$ pairs in the neutral and charged current production processes $e^- q \to e^- h_1 q$ and $e^- q\to ν_e h_1 q'$, respectively, at the planneded large Hadron electron Collider (LHeC), with an $e^-$ beam energy of 60 GeV and a $p$ beam energy of 7 TeV. We also focus on observing a relatively light charged Higgs boson ($h^{-}$) via its production mode $e^- b \to ν_e h^{-} b$ followed by the decays $h^{-} \to s \bar c + s \bar u$ at the upcoming Future Circular Collider in hadron-electron mode (FCC-eh) with $\sqrt s \approx 3.5$ TeV. We have performed our analysis in the framework of the Next-to-Minimal Supersymmetric Standard Model (NMSSM) wherein the intermediate Higgs boson ($h_2$) is Standard Model (SM)-like. We have considered constraints from Dark Matter (DM), superparticle and the Higgs boson data. In both analyses, we have carried out signal and background computations with selections optimized to the model at hand and found that in both cases it is possible to get large significances for low mass Higgs bosons.

hep-ph↗

arXiv2017

Production of a light top-squark pair in association with a light non-standard Higgs boson within the NMSSM at the 13 TeV LHC and a 33 TeV proton collider

We study the potential of the LHC accelerator, and a future 33 TeV proton collider, to observe the production of a light top squark pair in association with the lightest Higgs boson (${\tilde t}_1 {\tilde t}_1 h_1$), as predicted by the Next-to-Minimal Supersymmetric Standard Model (NMSSM). We scan randomly about ten million points of the NMSSM parameter space, allowing all possible decays of the lightest top squark and lightest Higgs boson, with no assumptions about their decay rates, except for known physical constraints such as perturbative bounds, Dark matter relic density consistent with recent Planck experiment measurements, Higgs mass bounds on the next to lightest Higgs boson, $h_2$, assuming it is consistent with LHC measurements for the Standard Model Higgs boson, LEP bounds for the chargino mass and Z invisible width, experimental bounds on B meson rare decays and some LHC experimental bounds on SUSY particle spectra different to the particles involved in our study. We find that for low mass top-squark, the dominating decay mode is ${\tilde t}_1 \rightarrow b \tildeχ_1^{\pm}$ with $\tildeχ_1^{\pm} \rightarrow W^{\pm} \tildeχ_1^0 $. We use three bench mark points with the highest cross sections, which naturally fall within the compressed spectra of the top squark, and make a phenomenological analysis to determine the optimal event selection that maximizes the signal significance over backgrounds. We focus on the leptonic decays of both $W$'s and the decay of lightest Higgs boson into b-quarks ($h_1 \rightarrow b \bar b$). Our results show that the high luminosity LHC will have limitations to observe the studied signal and only a proton collider with higher energy will be able to observe the SUSY scenario studied with more than three standard deviations over background.

hep-ph↗

arXiv2017

Light neutral CP-even Higgs boson within Next-to-Minimal Supersymmetric Standard model (NMSSM) at the Large Hadron electron Collider (LHeC)

We analyze the prospects of observing the light CP-even neutral Higgs bosons ($h_1$) in their decays into $b \bar b$ quarks, in the neutral and charged current production processes $e h_1 q$ and $νh_1 q$ at the upcoming LHeC, with $\sqrt s \approx 1.296$ TeV. Assuming that the intermediate Higgs boson ($h_2$) is Standard Model (SM)-like, we study the Higgs production within the framework of NMSSM. We consider the constraints from Dark-matter, Sparticle masses, and the Higgs boson data. The signal in our analysis can be classified as three jets, with electron (missing energy)coming from the neutral (charged) current interaction. We demand that the number of b-tagged jets in the central rapidity region be greater or equal to two. The remaining jet is tagged in the forward regions. With this forward jet and two $b$-tagged jets in the central region, we reconstructed three jets invariant masses. Applying some lower limits on these invariant masses turns out to be an essential criterion to enhance the signal--to--background rates, with slightly different sets of kinematical selections in the two different channels. We consider almost all reducible and irreducible SM background processes. We find that the non-SM like Higgs boson, $h_1$, would be accessible in some of the NMSSM benchmark points, at approximately 0.4$σ$ (2.5$σ$) level in the $e$+3j channel up to Higgs boson masses of 75 GeV and in the $E\!\!\!\!/_T$+3j channel could be discovered with 1.7$σ$ (2.4$σ$) level up to Higgs boson masses of 88 GeV with 100 fb$^{-1}$ of data in a simple cut-based (with optimization) selection. With ten times more data accumulation at the end of the LHeC run and using optimization, one can have 5$σ$ discovery in the electron (missing energy) channel up to 85 (more than 90) GeV.

hep-ph↗

arXiv2014

Testing SUSY models for the muon g-2 anomaly via Chargino-Neutralino Pair Production at the LHC

Non-universal gaugino mass models can naturally account for the dark matter relic density via the bulk annihilation process with relatively light bino LSP and right sleptons in the mass range of ~ 100 GeV, while accommodating the observed Higgs boson mass of ~ 125 GeV with TeV scale squark/gluino masses. A class of these models can also account for the observed muon g-2 anomaly via SUSY loops with wino and left sleptons in the mass range of 400 -- 700 GeV. These models can be tested at LHC via electroweak production of charged and neutral wino pair, leading to robust trilepton and same sign dilepton signals. We investigate these signals along with the standard model background for both 8 and 13 TeV LHC runs.

hep-ph↗

arXiv2014

Dilepton Signatures of the Higgs Boson with Tau-jet Tagging

We consider the process $p p \to t {\bar t} H$. This process can give rise to many signatures of the Higgs boson. The signatures can have electrons, muons and jets. We consider the signatures that have two electrons/muons and jets. Tagging of a tau jet and a bottom jet can help reduce the backgrounds significantly. In particular, we examine the usefulness of the signatures "isolated 2 electrons/muons + a bottom jet + a tau jet", "isolated 2 electrons/muons + 2 tau jets", "isolated 2 electrons/muons + 2 bottom jets + a tau jet", and "isolated 2 electrons/muons + a bottom jet + 2 tau jets". We find that signatures with two tau jets are useful. The signatures with one tau jet are also useful, if we restrict to same-sign electrons/muons. These requirements reduce the backgrounds due the process with Z-bosons + jets and the production of a pair of top quarks. We show that these signatures may be visible in the run II of the Large Hadron Collider.

hep-ph↗

arXiv2013

Multilepton Signatures of the Higgs Boson through its Production in Association with a Top-quark Pair

We consider the possible production of the Higgs Boson in association with a top-quark pair and its subsequent decay into a tau-lepton pair or a W-boson pair. This process can give rise to many signatures of the Higgs boson. These signatures can have electrons, muons, tau jets, bottom jets and/or light flavour jets. We analyze the viability of some of these signatures. We will look at those signatures where the background is minimal. In particular, we explore the viability of the signatures "isolated 4 electron/muon" and "isolated 3 electron/muon + a jet" The jet can be due to a light flavour quark/gluon, a bottom quark, or a tau lepton. Of all these signatures, we find that "isolated 3 electron/muon + a tau jet", with an extra bottom jet, can be an excellent signature of this mode of the Higgs boson production. We show that this signature may be visible within a year, once the Large Hadron Collider (LHC) restarts. Some of the other signatures would also be observable after the LHC accumulates sufficient luminosity.

hep-ph↗

arXiv2010

CP-violating Supersymmetric Higgs at the Tevatron and LHC

We analyze the prospect for observing the intermediate neutral Higgs boson ($h_2$) in its decay to two lighter Higgs bosons ($h_1$) at the presently operating hadron colliders in the framework of the CP violating MSSM using the PYTHIA event generator. We consider the lepton+ 4-jets+ $\met$ channel from associate $W h_2$ production, with $W h_2 \ra W h_1 h_1 \ra \ell ν_\ell b \bar b b\bar b$. We require two, three or four tagged $b$-jets. We explicitly consider all relevant Standard Model backgrounds, treating $c$-jets separately from light flavor and gluon jets and allowing for mistagging. We find that it is very hard to observe this signature at the Tevatron, even with 20 fb$^{-1}$ of data, in the LEP--allowed region of parameter space due to the small signal efficiency, even though the background is manageable. At the LHC, a priori huge SM backgrounds can be suppressed by applying judiciously chosen kinematical selections. After all cuts, we are left with a signal cross section of around 0.5 fb, and a signal to background ratio between 1.2 and 2.9. According to our analysis this Higgs signal should be viable at the LHC in the vicinity of present LEP exclusion once 20 to 50 fb$^{-1}$ of data have been accumulated at $\sqrt{s}=14$ TeV.

hep-ph↗

arXiv2010

CP-violating MSSM Higgs at Tevatron and LHC

We analyze the prospect for observing the intermediate neutral Higgs boson ($h_2$) in its decay to two lighter Higgs bosons ($h_1$) at the presently operating hadron colliders in the framework of the CP violating MSSM using the PYTHIA event generator. We consider the lepton+ 4-jets+ $\met$ channel from associate $W h_2$ production, with $W h_2 \ra W h_1 h_1 \ra \ell ν_\ell b \bar b b\bar b$. We require two or three tagged $b$-jets. We explicitly consider all relevant Standard Model backgrounds, treating $c$-jets separately from light flavor and gluon jets and allowing for mistagging. We find that it is very hard to observe this signature at the Tevatron, even with 20 fb$^{-1}$ of data, in the LEP--allowed region of parameter space due to the small signal efficiency. At the LHC, a priori huge SM backgrounds can be suppressed by applying judiciously chosen kinematical selections. After all cuts, we are left with a signal cross section of around 0.5 fb, and a signal to background ratio between 1.2 and 2.9. According to our analysis this Higgs signal should be viable at the LHC in the vicinity of present LEP exclusion once 20 to 50 fb$^{-1}$ of data have been accumulated at $\sqrt{s}=14$ TeV.

hep-ph↗

arXiv2008

Sneutrino LSPs in R-parity violating minimal supergravity models

We consider the minimal supergravity model (mSUGRA) with one additional R-parity violating operator at the GUT scale. The superparticles mass spectra at the weak scale are generally altered due to the presence of the R-parity violating coupling in the renormalization group equations. We show that a lepton number violating coupling at the GUT scale can lead to a sneutrino as the lightest supersymmetric particle (LSP) in a large region of parameter space consistent with the muon anomalous magnetic moment and other precision measurements. We also give characteristic collider signatures at the LHC.

hep-ph↗

arXiv2008

CP-violating Higgs at Tevatron

We analyze the prospect for observing the intermediate neutral Higgs ($h_2$) boson in its decay to two lighter Higgs bosons ($h_1$) at the Tevatron in the framework of the CP violating MSSM using the PYTHIA event generator. We consider the lepton+ 4-jets+ $\met$ channel from $p \bar p \ra W h_2 \ra W h_1 h_1 \ra l ν_l b \bar b b\bar b$, with two or three tagged $b$ jets. We found that it is very hard to observe this signature in the LEP-allowed region of parameter space, due to the small signal efficiency.

hep-ph↗

arXiv2007

Focus Point SUSY at the LHC Revisited

The estimation of the backgrounds for gluino signals in focus point supersymmetry is extended by including the backgrounds from the production of four third generation quarks in the analysis. We find that these backgrounds are negligible if one uses the strong selection criteria proposed in the literature (including this analysis) for heavy gluino searches. Softer selection criteria often recommended for lighter gluino searches yield backgrounds which are small but numerically significant. We have also repeated the more conventional background calculations and compared our results with the other groups. We find that the size of the total residual background estimated by different groups using different event generators and hard kinematical cuts agree approximately. In view of the theoretical uncertainties in the leading order signal and background cross sections mainly due to the choice of the QCD scale, the gluino mass reach at the LHC cannot be pinpointed. However, requiring a signal with $\rm\geq 3$ tagged b-jets (instead of the standard choice of $\rm\geq 2$) it is shown that gluino masses close to 2 TeV can be probed at the LHC for a range of reasonable choices of the QCD scale for an integrated luminosity of 300 fb$^{-1}$.

hep-ph↗

arXiv2006

Four body decay of the lighter top-squark constrained by the Lighter CP-even Higgs boson mass bound

We reinvestigated the parameter space allowing a large BR of the 4-body decay of the lighter top-squark ($\lstop$) accessible at Tevatron Run-II by imposing the lighter CP-even Higgs boson mass ($\mlhiggs$) bound from LEP. Important constraints were obtained in mSUGRA as well as in the unconstrained supersymmetric models. Our results show that the prospect of searching the lighter top-squark via the 4-body decay mode, in particular the $\ell + n-jets + \met$ signal, is not promising in mSUGRA due to the above bound on $\mlhiggs$. The existing bounds on $\mlstop$ from Tevatron Run-I and LEP assuming 100% BR of the loop decay of $\lstop$ are, therefore, valid to a good approximation. We also find that large BRs of the above 4-body decay are allowed in the unconstrained model over significant regions of parameter spaces and the possibility that this decay mode is the main discovery channel at Tevatron Run-II is open. We have briefly reviewed the theoretical uncertainties in the calculation of $\mlhiggs$ and their consequences for the constraints obtained by us. We have commented upon, with illustrative examples, how the above parameter space is affected if future experiments push the Higgs boson mass bound upward.

hep-ph↗

arXiv2006

Top squark and neutralino decays in a R-parity violating model constrained by neutrino oscillation data

In a R-parity violating (RPV) model of neutrino mass with three bilinear couplings $μ_i$ and three trilinear couplings $λ'_{i33}$, where $i$ is the lepton index, we find six generic scenarios each with a distinctive pattern of the trilinear couplings consistent with the oscillation data. These patterns may be reflected in direct RPV decays of the lighter top squark or in the RPV decays of the lightest superparticle, assumed to be the lightest neutralino. Typical signal sizes at the Tevatron RUN II and the LHC have been estimated and the results turn out to be encouraging.

hep-ph↗

arXiv2004

Top squark mass: current limits revisited and new limits from Tevatron Run-I

Analyzing the $\ell +n$-$jets+ \met$ (where $n \ge 2 $), data from Run-I of the Tevatron using the Bayesian technique, we obtain model independent limits on the product $\br(\lstop\ra be^{+}ν_e \lspone) \times \br(\lstop^{*}\ra \bar{b}q\bar{q^{\prime}}\lspone)$ for different values of the lighter top squark($\lstop$) mass and the lightest supersymmetric particle($\lspone$) mass. The SUSY signals have been simulated by interfacing the 4-body decay of $\lstop$ at the parton level with the event generator PYTHIA. These limits have been translated into exclusion plots in the $\mlstop$-$\mlspone$ plane, which also turn out to be fairly model independent for fixed values of the BR of the competing loop decay mode $\lstop\ra c \lspone$. Assuming the loop decay BR to be negligible and using the leading order cross section for $\lstoplstop$ pair production, we obtain conservatively $\mlstop \ge $77.0 (74.5) GeV for $\mlspone$=5(15) GeV, while for $\br(\lstop\ra c \lspone)$=20%, the corresponding limits are $\mlstop \ge $68.0 (65.0) GeV. Using the larger next to leading order cross-section stronger limits are obtained. For example, if $\br(\lstop\ra c \lspone)$=20%, $\mlstop \ge $73.0 (72.7) GeV for $\mlspone$=5(15) GeV. Our limits nicely complement the ALEPH bounds which get weaker for low $\mlspone$.

hep-ph↗

arXiv2003

Probing R-parity violating models of neutrino mass at the Tevatron via top Squark decays

We have estimated the limiting branching ratio of the R-parity violating (RPV) decay of the lighter top squark, $\tilde t_1 \ar l^+ d$ ($l=e$ or $μ$ and d is a down type quark of any flavor), as a function of top squark mass($\MST$) for an observable signal in the di-lepton plus di-jet channel at the Tevatron RUN-II experiment with 2 fb$^{-1}$ luminosity. Our simulations indicate that the lepton number violating nature of the underlying decay dynamics can be confirmed via the reconstruction of $\MST$. The above decay is interesting in the context of RPV models of neutrino mass where the RPV couplings ($λ'_{i3j}$) driving the above decay are constrained to be small ($\lsim 10^{-3} - 10^{-4} $). If $\tilde t_1$ is the next lightest super particle - a theoretically well motivated scenario - then the RPV decay can naturally compete with the R-parity conserving (RPC) modes which also have suppressed widths. The model independent limiting BR can delineate the parameter space in specific supersymmetric models, where the dominating RPV decay is observable and predict the minimum magnitude of the RPV coupling that will be sensitive to Run-II data. We have found it to be in the same ballpark value required by models of neutrino mass, for a wide range of $\MST$. A comprehensive future strategy for linking top squark decays with models of neutrino mass is sketched.

hep-ph↗