arXiv subjects

Satyanarayan Mukhopadhyay

Publications and source records attributed to Satyanarayan Mukhopadhyay.

At least 19 recordsLinked to original sources

arXiv2026

Finite Temperature NLO Corrections in Relativistic Scatterings: Implications for Dark Matter Freeze-In

We study the next-to-leading order (NLO) virtual and thermal corrections to relativistic $2 \rightarrow 2$ scattering processes involving scalar particles in the early Universe thermal plasma. Taking the example of freeze-in production of scalar dark matter pairs through these scatterings, we evaluate the impact of the NLO corrections to the annihilation rate and the dark matter yield. We find that including only thermal mass corrections to a leading order interaction rate can overestimate the reduction in these rates, and the full NLO corrections can modify the DM abundance predictions by $\mathcal{O}(30\%)$. It is also observed that while the virtual NLO effects are larger, the finite temperature NLO corrections to the matrix elements in the relativistic regime can modify the DM abundance by $\mathcal{O}(10\%)$, in comparison to the virtual NLO corrections.

hep-ph↗

arXiv2026

Prospects of measuring the atmospheric muon neutrino and anti-neutrino flux ratio with the ATLAS detector

There is a significant uncertainty in the prediction of atmospheric muon neutrino and anti-neutrino flux ratio using different flux models, especially at higher energies. We study the prospects of experimentally measuring this flux ratio as a function of energy with the ATLAS detector at the LHC. To this end, we compute the contained-vertex and external upward going charged current event rates induced by atmospheric muon (anti-)neutrinos through deep inelastic scattering at the 4 kiloton hadron calorimeter (HCAL) component of ATLAS. We illustrate the event selection criteria necessary to eliminate the cosmic ray muon background for the above event classes. While the contained vertex events have a striking topology with a muon being created inside the HCAL and then travelling to the muon chamber possibly through the tracker, for muons with energy larger than 3 GeV, nearly 10 times more events are obtained for the external upward going muons created in the rock column below the detector. Our estimates show that the energy dependence of the ratio of negative and positively charged muons induced by atmospheric muon neutrino and anti-neutrino fluxes can be measured by ATLAS upto a muon energy of 100 GeV, with 1000-live days of neutrino physics exposure over a period of several years, considering only the period with the LHC beams not in circulation, but the detector and magnetic fields of ATLAS in operation. With this exposure, we expect to obtain 60 $μ^-$ and 30 $μ^+$ contained vertex events, and $599~μ^-$ and $292~μ^+$ external upward-going events, after imposing the necessary selection criteria. For the latter class of events, this corresponds to an expected ratio of negative to positive charged muon events averaged over all energies, $R_{μ^-/ μ^+}=2.05^{+0.15}_{-0.14}$, at $68\%$ C.L. (Abridged)

hep-ph↗

arXiv2024

Cosmological implications of inflaton-mediated dark and visible matter scatterings after reheating

The initial density of dark matter (DM) particles, otherwise secluded from the standard model (SM), may be generated at reheating, with an initial temperature ratio for internal thermalizations, $ξ_i=T_{\rm DM,i}/T_{\rm SM,i}$. This scenario necessarily implies inflaton-mediated scatterings between DM and SM after reheating, with a rate fixed by the relic abundance of DM and the reheat temperature. These scatterings can be important for an inflaton mass and reheat temperature as high as $\mathcal{O}(10^7 {~\rm GeV})$ and $\mathcal{O}(10^9{~\rm GeV})$, respectively, since the thermally averaged collision terms become approximately independent of the inflaton mass when the bath temperature is larger than the mass. The impact of these scatterings on DM cosmology is studied modeling the perturbative reheating physics by a gauge-invariant set of inflaton interactions upto dimension-5 with the SM gauge bosons, fermions and the Higgs fields. It is observed that an initially lower (higher) DM temperature will rapidly increase (decrease), even with very small couplings to the inflaton. There is a sharp lower bound on the DM mass below which the relic abundance cannot be satisfied due to faster back-scatterings depleting DM quanta to SM particles. For low DM masses, the CMB constraints become stronger due to the collisions for $ξ_i<1$, probing values as small as $\mathcal{O}(10^{-4})$, and weaker for $ξ_i>1$. The BBN constraints become stronger due to the collisions for lower DM masses, probing $ξ_i$ as small as $\mathcal{O}(0.1)$, and weaker for higher DM mass. Thus inflaton-mediated collisions with predictable rates, relevant even for high-scale inflation models, can significantly impact the cosmology of light DM.

hep-ph↗

arXiv2022

Cannibal dark matter decoupled from standard model: cosmological constraints

An internally thermalized dark matter (DM) with only gravitational interaction with the standard model (SM) particles at low temperatures, may undergo number-changing self-scatterings in the early Universe, eventually freezing out to the observed DM abundance. If these reactions, such as a $3 \rightarrow 2$ process, take place when the DM is non-relativistic, DM cannibalizes itself to cool much slower than standard non-relativistic matter during the cannibal phase. As shown in earlier studies, if the cannibal phase takes place during the matter-dominated epoch, there are very strong constraints from structure formation. Considering scenarios in which the cannibal phase freezes out in the radiation-dominated epoch instead, we show that cannibal DM decoupled from the SM can be viable, consistent with all present cosmological constraints. To this end, we solve the coupled evolution equations of the DM temperature and density, and determine its abundance for different DM self-couplings. We then evaluate the constraints on these parameters from the cosmic-microwave background power spectrum, the big-bang nucleosynthesis limits on the relativistic degrees of freedom, the Lyman-$α$ limits on the DM free-streaming length and the theoretical upper bound on the $3 \rightarrow 2$ annihilation rate from $S-$matrix unitarity. We find that depending upon the DM self-couplings, a scalar cannibal DM with mass in the range of around 80 eV to 700 TeV can make up the observed DM density and satisfy all the constraints, when the initial DM temperature ($T_{\rm DM}$) is lower than the SM one ($T_{\rm SM}$), with $T_{\rm SM}/9100 \lesssim T_{\rm DM} \lesssim \,T_{\rm SM}/1.1$.

hep-ph↗

arXiv2022

Momentum distribution of dark matter produced in inflaton decay: effect of inflaton mediated scatterings

Post-inflationary reheating is a widely discussed mechanism for non-thermal production of dark matter (DM). In this scenario the momentum distribution of the produced DM particles is usually taken to be the one obtained at reheating, red-shifted at later times due to the expansion of the Universe. However, since in such a scenario both the DM and the standard model (SM) fields couple to the inflaton, the DM particles necessarily undergo self-scatterings, as well as elastic and inelastic scattering reactions with the SM bath, all of which proceed through $s-$channel or $t-$channel inflaton exchange. We compute the momentum distribution of the DM particles including the effect of these scatterings, and find that the distributions can be significantly altered, even though DM remains non-thermal throughout the cosmological evolution. We observe that if the inflaton dominantly couples to the SM Higgs boson through a renormalizable interaction, then reheating temperatures and inflaton masses at the TeV scale lead to a large effect from the scattering processes, with the DM-inflaton coupling constrained by the DM density. The scattering effects are found to be sensitive to the duration of the reheating process -- larger the duration, more momentum modes are filled at reheating, leading to an enhanced scattering probability. We also obtain the free-streaming length of such DM using the resulting non-thermal momentum distribution, which can be used to estimate the implications of the Lyman-$α$ constraints on the DM mass. It is observed that in the scenarios considered, including the scattering effects can reduce the DM average velocity at matter-radiation equality, and its free-streaming length, by upto a factor of $40$, thereby making the constraints on light DM produced in inflaton decay significantly weaker.

hep-ph↗

arXiv2021

Cosmology of complex scalar dark matter: interplay of self-scattering and annihilation

The cosmology of a standard model (SM) gauge singlet complex scalar dark matter (DM), stabilized by a reflection symmetry, is studied including all renormalizable interactions that preserve the reflection symmetry but can break the larger global U(1) symmetry of DM number. We find an interesting interplay of the ensuing DM self-scatterings and annihilations in generating the present DM density, and possible particle-antiparticle asymmetry in the DM sector. The role of DM self-scatterings in determining its present density and composition is a novel phenomenon. The simultaneous presence of the self-scatterings and annihilations is required to obtain a non-zero asymmetry, which otherwise vanishes due to unitarity sum rules.

hep-ph↗

arXiv2021

Revisiting the role of CP-conserving processes in cosmological particle-antiparticle asymmetries

We point out qualitatively different possibilities on the role of CP-conserving processes in generating cosmological particle-antiparticle asymmetries, with illustrative examples from models in leptogenesis and asymmetric dark matter production. In particular, we consider scenarios in which the CP-violating and CP-conserving processes are either both decays or both scatterings, thereby being naturally of comparable rates. This is in contrast to the previously considered CP-conserving processes in models of leptogenesis in different see-saw mechanisms, in which the CP-conserving scatterings typically have lower rates compared to the CP-violating decays, due to a Boltzmann suppression. We further point out that the CP-conserving processes can play a dual role if the asymmetry is generated in the mother sector itself, in contrast to the conventional scenarios in which it is generated in the daughter sector. This is because, the CP-conserving processes initially suppress the asymmetry generation by controlling the out-of-equilibrium number densities of the bath particles, but subsequently modify the ratio of particle anti-particle yields at the present epoch by eliminating the symmetric component of the bath particles through pair-annihilations, leading to a competing effect stemming from the same process at different epochs. We find that the asymmetric yields for relevant particle-antiparticle systems can vary by orders of magnitude depending upon the relative size of the CP-conserving and violating reaction rates.

hep-ph↗

arXiv2021

Unitarity limits on thermal dark matter in (non-)standard cosmologies

Using the upper bound on the inelastic reaction cross-section implied by S-matrix unitarity, we derive the thermally averaged maximum dark matter (DM) annihilation rate for general $k \rightarrow 2$ number-changing reactions, with $k \geq 2$, taking place either entirely within the dark sector, or involving standard model fields. This translates to a maximum mass of the particle saturating the observed DM abundance, which, for dominantly $s$-wave annihilations, is obtained to be around $130$ TeV, $1$ GeV, $7$ MeV and $110$ keV, for $k=2,3,4$ and $5$, respectively, in a radiation dominated Universe, for a real or complex scalar DM stabilized by a minimal symmetry. For modified thermal histories in the pre-big bang nucleosynthesis era, with an intermediate period of matter domination, values of reheating temperature higher than $\mathcal{O}(200)$ GeV for $k \geq 4$, $\mathcal{O}(1)$ TeV for $k=3$ and $\mathcal{O}(50)$ TeV for $k=2$ are strongly disfavoured by the combined requirements of unitarity and DM relic abundance, for DM freeze-out before reheating.

hep-ph↗

arXiv2020

Asymmetric dark matter from semi-annihilation

We show that a general semi-annihilation scenario, in which a pair of dark matter (DM) particles annihilate to an anti-DM, and an unstable state that can mix with or decay to standard model states, can lead to particle anti-particle asymmetry in the DM sector. The present DM abundance, including the CP-violation in the DM sector and the resulting present asymmetry are determined entirely by a single semi-annihilation process at next-to-leading order. For large CP-violation in this process, we find that a nearly complete asymmetry can be obtained in the DM sector, with the observed DM density being dominated by the (anti-)DM particle. The presence of additional pair-annihilation processes can modify the ratio of DM and anti-DM number densities further, if the pair-annihilation is active subsequent to the decoupling of the semi-annihilation. For such a scenario, the required CP-violation for generating the same present asymmetry is generically much smaller, as compared to the scenario with only semi-annihilation present. We show that a minimal model with a complex scalar DM with cubic self-interactions can give rise to both semi- and pair-annihilations, with the required CP-violation generated at one-loop level. We also find that the upper bound on the DM mass from S-matrix unitarity in the purely asymmetric semi-annihilation scenario, with maximal CP-violation, is around 15 GeV, which is much stronger than in the WIMP and previously considered asymmetric DM cases, due to the required large non-zero chemical potential for such asymmetric DM.

hep-ph↗

arXiv2019

Dark Matter Blind Spots at One-Loop

We evaluate the impact of one-loop electroweak corrections to the spin-independent dark matter (DM) scattering cross-section with nucleons ($σ_{\rm SI}$), in models with a so-called blind spot for direct detection, where the leading-order prediction for the relevant DM coupling to the Higgs boson, and therefore $σ_{\rm SI}$, are vanishingly small. Adopting a simple illustrative scenario in which the DM state results from the mixing of electroweak singlet and doublet fermions, we compute the relevant higher order corrections to the scalar effective operator contributions to $σ_{\rm SI}$, stemming from both triangle and box diagrams involving the SM and dark sector fields. It is observed that in a significant region of the singlet-doublet model-space, the one-loop corrections ``unblind'' the tree-level blind spots and lead to detectable SI scattering rates at future multi-ton scale liquid Xenon experiments, with $σ_{\rm SI}$ reaching values up to a few times $10^{-47} {~\rm cm}^2$, for a weak scale DM with $\mathcal{O}(1)$ Yukawa couplings. Furthermore, we find that there always exists a new SI blind spot at the next-to-leading order, which is perturbatively shifted from the leading order one in the singlet-doublet mass parameters. For comparison, we also present the tree-level spin-dependent scattering cross-sections near the SI blind-spot region, that could lead to a larger signal. Our results can be mapped to the blind-spot scenario for bino-Higgsino DM in the MSSM, with other sfermions, the heavier Higgs boson, and the wino decoupled.

hep-ph↗

arXiv2019

Electroweak Dark Matter at Future Hadron Colliders

In a large class of scenarios, dark matter (DM) particles that belong to a multiplet of the standard model (SM) weak interactions are challenging to probe in direct detection experiments due to loop-suppressed cross-sections. Direct production at colliders is thus crucial to look for such DM candidates, and under current estimates, future runs of the 14-TeV LHC are projected to probe masses of around 300 GeV for DM belonging to an SU(2) doublet (Higgsino-like), and 900 GeV for SU(2) triplet (wino-like). We examine how far this mass reach can be extended at the proposed 27-TeV high-energy upgrade of the LHC (HE-LHC), and compare the results to the case for a 100-TeV hadron collider. Following a detector setup similar to that of the ATLAS tracking system for the Run-2 LHC upgrade, with a new Insertable B-Layer (IBL), a disappearing charged track analysis at the HE-LHC can probe Higgsino-like (wino-like) DM mass of up to 600 GeV (2.1 TeV) at the 95% C.L. The monojet and missing transverse momentum search, on the otherhand, has a weaker reach of 490 GeV (700 GeV) at 95% C.L. for the Higgsino-like (wino-like) states. The mass range accessible in the collider searches can be complementary to the indirect detection probes using gamma rays from dwarf-spheroidal galaxies.

hep-ph↗

arXiv2018

Higgs Couplings at High Scales

We study the off-shell production of the Higgs boson at the LHC to probe Higgs physics at higher energy scales utilizing the process $g g \rightarrow h^{*} \rightarrow ZZ$. We focus on the energy scale dependence of the off-shell Higgs propagation, and of the top quark Yukawa coupling, $y_t (Q^2)$. Extending our recent study in arXiv:1710.02149, we first discuss threshold effects in the Higgs propagator due to the existence of new states, such as a gauge singlet scalar portal, and a possible continuum of states in a conformal limit, both of which would be difficult to discover in other traditional searches. We then examine the modification of $y_t (Q^2)$ from its Standard Model (SM) prediction in terms of the renormalization group running of the top Yukawa, which could be significant in the presence of large flat extra-dimensions. Finally, we explore possible strongly coupled new physics in the top-Higgs sector that can lead to the appearance of a non-local $Q^2$-dependent form factor in the effective top-Higgs vertex. We find that considerable deviations compared to the SM prediction in the invariant mass distribution of the $Z$-boson pair can be conceivable, and may be probed at a $2σ$-level at the high-luminosity 14 TeV HL-LHC for a new physics scale up to $\mathcal{O}(1 {~\rm TeV})$, and at the upgraded 27 TeV HE-LHC for a scale up to $\mathcal{O}(3 {~\rm TeV})$. For a few favorable scenarios, $5σ$-level observation may be possible at the HE-LHC for a scale of about $\mathcal{O}(1 {~\rm TeV})$.

hep-ph↗

arXiv2018

Off-shell Higgs Probe to Naturalness

Examining the Higgs sector at high energy scales through off-shell Higgs production can potentially shed light on the naturalness problem of the Higgs mass. We propose such a study at the LHC by utilizing a representative model with a new scalar field ($S$) coupled to the Standard Model Higgs doublet ($H$) in a form $ |S|^2 |H|^2$. In the process $p p \rightarrow h^* \rightarrow ZZ$, the dominant momentum-dependent part of the one-loop scalar singlet corrections, especially above the new threshold at $2m_S$, leads to a measurable deviation in the differential distribution of the $Z$-pair invariant mass, in accordance with the quadratic divergence cancellation to the Higgs mass. We find that it is conceivable to probe such new physics at the $5σ$ level at the high-luminosity LHC, improving further with the upgraded $27$ TeV LHC, without requiring the precise measurement of the Higgs boson total width. The discovery of such a Higgs portal could also have important implications for thermal dark matter as well as for electroweak baryogenesis.

hep-ph↗

arXiv2018

Closing in on the chargino contribution to the muon g-2 in the MSSM: current LHC constraints

We revisit the current LHC constraints on the electroweak-ino sector parameters in the minimal supersymmetric standard model (MSSM) that are relevant to explaining the $(g-2)_μ$ anomaly via the dominant chargino and muon sneutrino loop. Since the LHC bounds on electroweak-inos become weaker if they decay via an intermediate stau or a tau sneutrino instead of the first two generation sleptons, we perform a detailed analysis of the scenario with a bino as the lightest supersymmetric particle (LSP) and a light stau as the next-to-lightest one (NLSP). Even in this scenario, the chargino sector parameters in the MSSM that can account for the $(g-2)_μ$ anomaly within $1 σ$ are already found to be significantly constrained by the 8 TeV LHC and the available subset of the 13 TeV LHC limits. We also estimate the current LHC exclusions in the left-smuon (and/or left-selectron) NLSP scenario from multilepton searches, and further combine the constraints from the multi-tau and multi-lepton channels for a mass spectrum in which all three generations of sleptons are lighter than the chargino. In the latter two cases, small corners of the $1 σ$ favoured region for $(g-2)_μ$ are still allowed at present.

hep-ph↗

arXiv2017

Boosted Dark Matter and its implications for the features in IceCube HESE data

We study the implications of the premise that any new, relativistic, highly energetic neutral particle that interacts with quarks and gluons would create cascade-like events in the IceCube (IC) detector. Such events would be observationally indistinguishable from neutral current deep-inelastic scattering events due to neutrinos. Consequently, one reason for deviations, breaks or excesses in the expected astrophysical power-law neutrino spectrum could be the flux of such a particle. Motivated by features in the recent 1347-day IceCube high energy starting event data (HESE), we focus on particular boosted dark matter ($χ$) related realizations of this premise. Here, $χ$ is assumed to be much lighter than, and the result of, the slow decay of a massive scalar ($ϕ$) which constitutes a major fraction of the Universe's dark matter. We show that this hypothesis, coupled with a standard power-law astrophysical neutrino flux is capable of providing very good fits to the present data, along with a possible explanation of other features in the HESE sample. These features include a) the paucity of events beyond $\sim 2$ PeV b) a spectral feature resembling a dip or a spectral change in the 400 TeV--1 PeV region and c) an excess in the $50-100$ TeV region. We consider two different boosted DM scenarios, and determine the allowed mass ranges and couplings for four different types of mediators (scalar, pseudoscalar, vector and axial-vector) which could connect the standard and dark sectors. We consider constraints from gamma-ray observations and collider searches. We find that the gamma-ray observations provide the most restrictive constraints, disfavouring the $1σ$ allowed parameter space from IC fits, while still being consistent with the $3σ$ allowed region. We also test our proposal and its implications against IC's recent six-year through-going muon track data.

hep-ph↗

arXiv2016

Measuring the CP property of Higgs coupling to tau leptons in the VBF channel at the LHC

We study the prospects of measuring the CP property of the Higgs ($h$) coupling to tau leptons using the vector boson fusion (VBF) production mode at the high-luminosity LHC. Utilizing the previously proposed angle between the planes spanned by the momentum vectors of the $(π^+π^0)$ and $(π^- π^0)$ pairs originating in $τ^\pm$ decays as the CP-odd observable, we perform a detailed Monte Carlo analysis, taking into account the relevant standard model backgrounds, as well as detector resolution effects. We find that excluding a pure CP-odd coupling hypothesis requires $\mathcal{O}(400 {~\rm fb}^{-1})$ luminosity at the 14 TeV LHC, and values of the CP-mixing angle larger than about $25^\circ$ can be excluded at $95\%$ confidence level using $3 {~\rm ab}^{-1}$ data. It is observed that the uncertainty in the angular resolution of the neutral pion momenta does not constitute a significant hurdle. Achieving a signal to background ratio ($S/B$) close to one, while keeping a high enough signal yield required to study the angular distributions selects out VBF as a promising mode to probe the CP nature of the $hττ$ coupling, with gluon fusion suffering from a low $S/B$, and the $W^\pm h/Zh$ mode (with leptonically decaying $W^\pm /Z$) having a much smaller signal rate.

hep-ph↗

arXiv2016

Quark-gluon discrimination in the search for gluino pair production at the LHC

We study the impact of including quark- and gluon-initiated jet discrimination in the search for strongly interacting supersymmetric particles at the LHC. Taking the example of gluino pair production, considerable improvement is observed in the LHC search reach on including the jet substructure observables to the standard kinematic variables within a multivariate analysis. In particular, quark and gluon jet separation has higher impact in the region of intermediate mass-gap between the gluino and the lightest neutralino, as the difference between the signal and the standard model background kinematic distributions is reduced in this region. We also compare the predictions from different Monte Carlo event generators to estimate the uncertainty originating from the modelling of the parton shower and hadronization processes.

hep-ph↗

arXiv2016

Effective Theory of WIMP Dark Matter supplemented by Simplified Models: Singlet-like Majorana fermion case

We enumerate the set of simplified models which match onto the complete set of gauge invariant effective operators up to dimension six describing interactions of a singlet-like Majorana fermion dark matter with the standard model. Tree level matching conditions for each case are worked out in the large mediator mass limit, defining a one to one correspondence between the effective operator coefficients and the simplified model parameters for weakly interacting models. Utilizing such a mapping, we compute the dark matter annihilation rate in the early universe, as well as other low-energy observables like nuclear recoil rates using the effective operators, while the simplified models are used to compute the dark matter production rates at high energy colliders like LEP, LHC and future lepton colliders. Combining all relevant constraints with a profile likelihood analysis, we then discuss the currently allowed parameter regions and prospects for future searches in terms of the effective operator parameters, reducing the model dependence to a minimal level. In the parameter region where such a model-independent analysis is applicable, and leaving aside the special dark matter mass regions where the annihilation proceeds through an s-channel Z or Higgs boson pole, the current constraints allow effective operator suppression scales ($Λ$) of the order of a few hundred GeV for dark matter masses $m_χ>$ 20 GeV at $95\%$ C.L., while the maximum allowed scale is around $3$ TeV for $m_χ\sim \mathcal{O}(1\,{\rm TeV})$. An estimate of the future reach of ton-scale direct detection experiments and planned electron-positron colliders show that most of the remaining regions can be probed, apart from dark matter masses near half of the Z-boson mass (with $500\,{\rm GeV} < Λ< 2\,{\rm TeV} $) and those beyond the kinematic reach of the future lepton colliders.

hep-ph↗