arXiv subjects

Ashok Goyal

Publications and source records attributed to Ashok Goyal.

At least 19 recordsLinked to original sources

arXiv2026

Dark Photon - ALP Freeze-in: 511 keV and H$\alpha$ Constraints

We investigate a freeze-in scenario of two component dark matter consisting of an axion-like particle (ALP) and a dark photon. The dark sector connects to the Standard Model through a dimension-five ALP-dark photon interaction, while a small kinetic mixing governs dark photon decays. Solving the coupled Boltzmann equations, we determine the parameter space consistent with the observed relic abundance. We find that, for a nearly degenerate dark sector, dark photon decay into an electron-positron pair through the kinetic mixing explains the Galactic 511 keV line while the dimension five operator can source the necessary production of dark photon and ALP particles to satisfy the relic density. We further confront the model with recent H$\alpha$ observations of dwarf galaxies, together with constraints from the cosmic microwave background, diffuse gamma rays, direct detection and collider searches. We identify viable regions of parameter space yielding $\Omega_{\rm DM}h^2\simeq0.12$, with an effective scale $\Lambda\sim10^{10}$-$10^{12}$ GeV, and dark photon lifetimes of order $10^{26}$-$10^{29}$ s, while remaining consistent with the observed 511 keV photon flux, $H\alpha$ constraints from Leo T and all other astrophysical constraints.

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arXiv2025

Comprehensive Constraints on ALP Couplings from future $e^+e^-$ Colliders, Muon $g-2$, Thermal Dark Matter and Higgs Measurements

In this article, we present projected 95\% C.L. limits on Axion-Like Particle (ALP) couplings from ALP production at a future $e^+e^-$ collider operating at $\sqrt{s} = 250~\text{GeV}$ with integrated luminosity $L = 0.5~\text{ab}^{-1}$. We constrain the effective couplings $g_{\gamma\gamma}$, $g_{Z\gamma}$, $g_{ZZ}$, and $g_{WW}$ over the ALP mass range $20~\text{GeV} \leq m_a \leq 100~\text{GeV}$, finding projected bounds at the level of $\mathcal{O}(10^{-1})~\text{TeV}^{-1}$ for $g_{\gamma\gamma}/f_a$. Given that the latest muon anomalous magnetic moment measurement ($\Delta a_\mu$) shows no statistically significant deviation from the Standard Model prediction, we reinterpret the ALP contributions to $\Delta a_\mu$ as a stringent consistency requirement. We then derive the corresponding allowed regions for $g_{\gamma\gamma}$ and the ALP--muon coupling $C_{\mu\mu}$, and apply them to a fermionic dark matter scenario in which the relic density depends on both the dark matter mass $m_\chi$ and $m_a$. The same parameter space is further constrained by Higgs signal strength measurements through $h \to \gamma\gamma$ and $h \to Z\gamma$. A comparative analysis with existing experimental and theoretical bounds highlights the complementarity of $\Delta a_\mu$, dark matter, and Higgs observables in restricting ALP couplings, demonstrating that even in the absence of a $\Delta a_\mu$ anomaly, these constraints provide essential guidance for viable ALP parameter space.

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arXiv2025

Higgs Decay Signal Strengths in an Extended 2HDM

The combined CMS and ATLAS analysis of $h \to Z\gamma$ reveals a $2\sigma$ excess over the Standard Model (SM) prediction, hinting at potential new physics. In contrast, the observed agreement of $\mu_{\gamma\gamma}$ with the SM imposes stringent constraints on such extension. In this context, we investigate a Two Higgs Doublet Model (2HDM) extended by a complex scalar singlet and a vector-like lepton (VLL). This framework successfully accommodates the Higgs decay signal strengths $\mu_{{}_{W \,W^\star}}$, $ \mu_{Z\gamma}\,$, and $\, \mu_{\gamma\gamma}$ while also satisfying precision electroweak constraints, the observed experimental value of muon $g-2$, and bounds from LEP II data. We identify a viable region of parameter space that is consistent with all low energy data and current experimental limits on the Higgs decay signal strengths.

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arXiv2024

$W-$mass and Muon $g-2$ in Inert 2HDM Extended by Singlet Complex Scalar

The deviations of the recent measurements of the muon magnetic moment and the $W-$boson mass from their SM predictions hint to new physics beyond the SM. In this article, we address the observed discrepancies in the $W$-boson mass and muon anomalous magnetic moment in the Inert Two Higgs Doublet Model (I2HDM) extended by a complex scalar field singlet under the SM gauge group. The model is constrained from the existing LEP data and the measurements of partial decay widths to gauge bosons at LHC. It is shown that a large subset of this constrained parameter space of the model can simultaneously accommodate the $W$-boson mass and also explain the muon $g-2$ anomaly.

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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.

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arXiv2023

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 $W^+W^-$, $\gamma\gamma$, $ZZ$, and $Z\gamma$-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 $g_{WW}$, $g_{\gamma\gamma}$, $g_{ZZ}$, and $g_{Z\gamma}$. To achieve this, we utilize a multiple-bin $\chi^2$ 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 $g_{\gamma\gamma}$ ($g_{WW}$, $g_{ZZ}$, $g_{Z\gamma}$) 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.

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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.

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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.

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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.

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arXiv2021

Leptonic $g-2$ anomaly in an extended Higgs sector with vector-like leptons

We address the observed discrepancies in the anomalous magnetic dipole moments (MDM) of the muon and electron by extending the inert two Higgs Doublet Model (2HDM) with SM gauge singlet complex scalar field and singlet Vector-like Lepton (VLL) field. We obtain the allowed parameter space constrained from the Higgs decays to gauge Bosons at LHC, LEP II data and electro-weak precision measurements. The muon and electron MDM's are then explained within a common parameter space for different sets of allowed couplings and masses of the model particles.

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arXiv2020

Effective Field Theory approach to lepto-philic self conjugate dark matter

We study the self conjugate dark matter (DM) particles interacting primarily with the standard model leptons in an effective field theoretical frame work. We consider SM gauge invariant effective contact interactions between the Majorana fermion, real scalar and a real vector DM with leptons by evaluating the Wilson coefficients appropriate for interaction terms upto dimension-8 and obtain constraints on the parameters of the theory from the observed relic density, indirect detection observations and from the DM-electron scattering cross-sections in the direct detection experiments. Low energy LEP data has been used to study sensitivity in the pair production of such low mass $\le$ 80 GeV DM particles. Pair production of DM particles of mass $\ge$ 50 GeV in association with mono-photons at the proposed ILC has rich potential to probe such effective operators.

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arXiv2020

Connecting the Muon Anomalous Magnetic Moment and the Multi-lepton Anomalies at the LHC

A number of predictions were made in von Buddenbrock et al (2016 Eur. Phys. J. C 76, 10, 580) pertaining to the anomalous production of multiple leptons at the Large Hadron Collider. Discrepancies in multi-lepton final states have now become statistically compelling with the available Run~2 data. These could be connected with a heavy boson, $H$, decaying predominantly into a SM Higgs boson, $h$, and a singlet scalar, $S$, where $m_H\approx 270$\,GeV and $m_S\approx 150$\,GeV. These can be embedded into a scenario where a Two Higgs Doublet is considered with an additional singlet scalar, 2HDM+S. The long-standing discrepancy in the muon anomalous magnetic moment, $Δa_μ$, is interpreted in the context of the 2HDM+S type-II and type-X, along with additional fermionic degrees of freedom. The 2HDM+S model alone with the constraints from the LHC data does not seem to explain the $Δa_μ$ anomaly. However, adding fermions with mass of order $\mathcal{O}(100)$\,GeV can explain the discrepancy for low enough values of fermion-scalar couplings.

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arXiv2019

Dark matter in the Randall-Sundrum model with non-universal coupling

We consider simplified dark matter models (DM) interacting gravitationally with the standard model (SM) particles in a Randall-Sundrum (RS) framework. In this framework, the DM particles interact through the exchange of spin-2 Kaluza-Klein (KK) gravitons in the $s$-channel with the SM particles. The parameter space of the RS model with universal couplings to SM particles is known to be strongly constrained from the LHC data. We are thus led to consider models with non-universal couplings. The first model we consider in this study is a top-philic graviton model in which only the right-handed top quarks are taken to interact strongly with the gravitons. In the second, the lepto-philic model, we assume that only the right-handed charged leptons interact strongly with the gravitons. We extend the study to include not only the scalar, vector and spin-1/2 fermions but also spin-3/2 fermionic dark matter. We find that there is a large parameter space in these benchmark models where it is possible to achieve the observed relic density consistent with the direct and indirect searches and yet not to be constrained from the LHC data.

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arXiv2019

Dark matter in the Randall-Sundrum model

In Ref. \cite{Goyal:2019vsw}, we had considered simplified dark matter models interacting gravitationally with the Standard Model particles in a Randall-Sundrum frame work where models are considered with non-universal couplings. In the top-philic graviton model the right-handed top quarks are taken to interact strongly with the gravitons and in the lepton-philic model, we assume that only the right-handed charged leptons interact strongly with the gravitons. We extend the study to include not only the scalar, vector and spin-1/2 fermions but also spin-3/2 fermionic dark matter. We find that there is a large parameter space in these benchmark models where it is possible to achieve the observed relic density consistent with the direct and indirect searches, which are also consistent with the data from Large Hadron Collider.

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arXiv2019

Lepto-philic 2-HDM + singlet scalar portal induced fermionic dark matter

We explore the possibility that the discrepancy in the observed anomalous magnetic moment of the muon $Δa _μ$ and the predicted relic abundance of Dark Matter by Planck data, can be explained in a lepto-philic 2-HDM augmented by a real SM singlet scalar of mass $\sim$ 10-80 GeV. We constrain the model from the observed Higgs Decay width at LHC, LEP searches for low mass exotic scalars and anomalous magnetic moment of an electron $Δa_e$. This constrained light singlet scalar serves as a portal for the fermionic Dark Matter, which contributes to the required relic density of the universe. A large region of model parameter space is found to be consistent with the present observations from the Direct and Indirect DM detection experiments.

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arXiv2018

Spin-3/2 dark matter in a simple $t$-channel model

We consider a spin-3/2 fermionic dark matter (DM) particle interacting with the Standard Model quarks through the exchange of a charged and coloured scalar or vector mediator in a simple $t$-channel model. It is found that for the vector mediator case, almost the entire parameter space allowed by the observed relic density is already ruled out by the direct detection LUX data. No such bounds exist on the interaction mediated by scalar particles. Monojet + missing energy searches at the Large Hadron Collider provide the most stringent bounds on the parameters of the model for this case. The collider bounds put a lower limit on the allowed DM masses.

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arXiv2018

Spin-$0^\pm$ portal induced Dark Matter

Standard model (SM) spin-zero singlets are constrained through their di-Bosonic decay channels via an effective coupling induced by a vector-like quark (VLQ) loop at the LHC for $\sqrt{s}$ = 13 TeV. These spin-zero resonances are then considered as portals for scalar, vector or fermionic dark matter particle interactions with SM gauge bosons. We find that the model is validated with respect to the observations from LHC data and from cosmology, indirect and direct detection experiments for an appreciable range of scalar, vector and fermionic DM masses greater than 300 GeV and VLQ masses $\ge$ 400 GeV, corresponding to the three choice of portal masses 270 GeV, 500 GeV and 750 GeV respectively.

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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.

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