arXiv subjects

Garv Chauhan

Publications and source records attributed to Garv Chauhan.

At least 19 recordsLinked to original sources

arXiv2026

Supernova Gamma-Ray Echo as an Astrophysical Near Detector for Galactic Neutrino Propagation

Core-collapse supernova neutrinos offer a unique probe of physics beyond the Standard Model over Galactic baselines. Yet even a high-statistics nearby burst may be limited by source uncertainties, especially for propagation effects that average over energy and appear only as an overall flux suppression. Inspired by near--far comparisons in terrestrial oscillation experiments, we show that next-generation MeV observations of the supernova gamma-ray echo---the delayed 511 keV signal induced by the neutrino burst in the stellar envelope---can serve as an astrophysical near detector for the emitted $\barν_e$ fluence. Comparing this echo-inferred source fluence with the surviving flux measured at Earth gives a direct test of neutrino propagation between the stellar surface and the detector. For pseudo-Dirac neutrinos, this turns the fully averaged active--sterile oscillation regime from an unobservable source-normalization ambiguity into a measurable near--far deficit, with sensitivity for nearby progenitors to splittings $δm^2\gtrsim 10^{-18}~{\rm eV}^2(0.22~{\rm kpc}/D)(E_\star/15~{\rm MeV})$. The same near--far logic also applies to other propagation-induced modifications of the observed flux, including neutrino decay and neutrino interactions with Galactic dark matter.

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arXiv2026

Gamma-Ray Echo as a Probe of Supernova Neutrino Emission Anisotropy and Long-Baseline Effects

During a core-collapse supernova (CCSN), the emitted electron antineutrino ($\barν_e$) burst initiates inverse beta decay (IBD) in the outer hydrogen layer of the stellar envelope. This leads to the production of a characteristic 511 keV photon signal, termed the Gamma-Ray Echo. The same neutrino burst, when detected on Earth in large neutrino observatories such as Hyper-Kamiokande, will offer information about the $\barν_e$ content of the neutrino flux reaching Earth. In this work, we show that comparing the $\barν_e$ content inferred from the gamma-ray echo with that inferred from terrestrial neutrino observations during a nearby CCSN event can offer a promising probe of large neutrino emission anisotropies and long-baseline propagation effects. In the latter case, the combined SN-Earth observations effectively act as a near-far detector configuration for neutrino propagation over an astrophysical baseline. We find that, for a near-Earth supernova, anisotropies or non-standard propagation effects at the level of tens of percent can be tested using gamma-ray telescopes with effective areas of $\mathcal{O}(10^4)~\mathrm{ cm^2}$. Therefore, our results motivate the development of the next generation of large effective area gamma-ray telescopes operating in the MeV gap.

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arXiv2026

The Dark Matter Diffused Supernova Neutrino Background

We consider neutrinos scattering off Milky Way dark matter and the impact of this scattering on supernovae neutrinos. This can take the form of attenuation on the initial flux of neutrinos and a time-delayed flux of scattered neutrinos. Considering dark matter masses above 100 MeV and past Milky Way supernovae, we find this time-delayed flux is nearly constant in time. We call this flux the Dark Matter Diffused Supernova Neutrino Background (DMDSNB), and use Super-K limits on the Diffuse Supernova Neutrino Background (DSNB) flux to set limits on the dark matter-neutrino scattering cross section. We find $σ_{\rm DM-ν}/m_{\rm DM} \lesssim 2.4 \times 10^{-24} \mathrm{cm^2}$/GeV for $m_{\rm DM} \gtrsim 1$ GeV, which is the strongest bound to date on dark matter-neutrino scatterings at MeV energies, and stronger than bounds set from SN1987A neutrino attenuation by an order of magnitude. We end by discussing how the DMDSNB could be distinguished from the DSNB.

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arXiv2025

511 keV Gamma Ray Echo from Particle Decays in Supernovae

The formation of a hot and dense core in a core-collapse supernova (SN) can produce massive Beyond Standard Model (BSM) particles. These particles can decay in the stellar envelope, generating positrons either directly or through secondary processes involving neutrinos or photons. We show for the first time that such positrons regardless of their production channel, can thermalize and annihilate at rest with ambient electrons in the outer SN envelope, producing a characteristic echo of 511 keV gamma rays. For axion-like particles (ALPs), we derive bounds on the ALP-photon coupling ($G_{a γ}$) using Pioneer Venus Orbiter observations of SN 1987A. We also evaluate the sensitivity of upcoming MeV gap gamma-ray telescopes in the 511 keV range, such as COSI and AMEGO, for future Galactic SNe, which can improve existing constraints or enable ALP discovery. The echo signal is a generic prediction for any particle species that efficiently produces positrons near the stellar surface.

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arXiv2025

LIQUIDating the Gallium Anomaly

The gallium anomaly has a global significance of greater than $5σ$. Most viable BSM solutions quickly run into strong tensions with reactor and solar neutrino data. We propose to use indium (${}^{115}\text{In}$) as a target as it offers a low threshold and reasonably high cross section. The neutrino-indium charged current cross section can be calibrated using the well-constrained solar ${}^{7}\text{Be}$ neutrino flux that lies very close in energy to the ${}^{51}\text{Cr}$ neutrino lines. The triple coincidence provided by ${}^{115}\text{In}$ neutrino capture can be fully exploited by an opaque scintillation detector that also provides energy and position information. We show that a $100$ ton indium target combined with 2 source runs of a $3.4$ MCi ${}^{51}\text{Cr}$ source can probe the complete parameter space of the gallium anomaly, both in the context of a vanilla sterile neutrino as well as more involved BSM scenarios.

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arXiv2025

Low-Energy Supernovae Bounds on Sterile Neutrinos

Sterile neutrinos can be produced through mixing with active neutrinos in the hot, dense core of a core-collapse supernova (SN). The standard bounds on the active-sterile mixing ($\sin^2 θ$) from SN arise from SN1987A energy-loss, requiring $E_{\text{loss}}<10^{52}~{\rm erg}$. In this work, we discuss a novel bound on sterile neutrino parameter space arising from the energy deposition through its decays inside the SN envelope. Using the observed underluminous SN IIP population, this energy deposition is constrained to be below $\sim 10^{50}~{\rm erg}$. Focusing on sterile neutrino mixing only with tau neutrino, for heavy sterile masses $m_s$ in the range $100$-$500$ MeV, we find stringent constraints on $\sin^2 θ_τ$ reaching two orders of magnitude lower than those from the SN1987A energy loss argument, {thereby probing the mixing angles required for Type-I seesaw mechanism}. Similar bounds will also be applicable to sterile mixing only with muons ($\sin^2 θ_μ$).

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arXiv2025

Neutron Stars as a Probe of Cosmic Neutrino Background

The Cosmic Neutrino Background (C$ν$B) constitutes the last observable prediction of the standard cosmological model, which has yet to be detected directly. In this work, we show how the coherent scattering of neutrinos off dense neutron matter can lead to an additional cooling channel in neutron stars (NSs). We also include the effects of gravitational capture and boosting, but find that the cooling is efficient only in the presence of large overdensities. We further discuss the prediction of a boosted C$ν$B flux on Earth from nearby NSs and the potential detection prospects in the case of a future nearby galactic supernova. Although currently these ideas do not offer any detection prospects, they can be used to constrain overdensities $η\lesssim 10^{11}\textrm{-}10^{14}$ on short length scales $\mathcal{O}(10\text{ km})$. We also discuss the impact of new physics scenarios, such as long-range forces, on NS cooling through the C$ν$B.

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arXiv2025

Supernova Gamma-Ray Constraints from Heavy Sterile Neutrino Decays

Heavy sterile neutrinos can be produced in core-collapse supernovae (CCSNe), which are superb particle generators because of their high densities and temperatures. If the sterile neutrinos are long-lived, these may be produced inside the supernova core and escape the stellar envelope, later decaying into SM particles like photons and neutrinos. In this work, we first improve the calculation of the $γ$-ray fluxes. We then revisit the bounds on the sterile neutrino parameter space from the non-observation of $γ$-rays from SN1987A by the Solar Maximum Mission (SMM) and constraints from the diffuse $γ$-ray background arising from sterile neutrino decays. We find that the constraints arising from both the SMM data and the diffuse $γ$-ray background are weaker than those that have previously appeared in the literature. Finally, we study the sensitivity of several present and near-future $γ$-ray telescopes such as e-ASTROGAM and Fermi-LAT, assuming a nearby future galactic CCSN. We show that future observations can probe mixing angles as low as $|U_{τ/\mu4}|^2\sim 5\times10^{-17}$.

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arXiv2024

Impact of the cosmic neutrino background on long-range force searches

Light bosons can mediate long-range forces. We show that light bosonic mediators interacting with a background medium, in particular, with the cosmic neutrino background (C$ν$B), may induce medium-dependent masses which could effectively screen long-range forces from detection. This leads to profound implications for long-range force searches in e.g. the Eöt-Wash, MICROSCOPE, and lunar laser-ranging (LLR) experiments. For instance, we find that when the coupling of the mediator to neutrinos is above $3\times10^{-10}$ or $5\times10^{-13}$, bounds from LLR and experiments employing the Sun as an attractor, respectively, would be entirely eliminated. Larger values of the coupling can also substantially alleviate bounds from searches conducted at shorter distances.

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arXiv2024

Collider Tests of Flavored Resonant Leptogenesis in the $U(1)_X$ Model

We study the generation of baryon asymmetry through the flavored resonant leptogenesis in the $U(1)_X$ extension of the Standard Model. Being a generalization of the $U(1)_{B\text{-}L}$, $U(1)_X$ is an ultraviolet-complete model of the right-handed neutrinos (RHNs), whose CP violating out-of-equilibrium decays lead to the generation of baryon asymmetry via leptogenesis. We can also explain the neutrino masses via the seesaw mechanism in this model. We consider three different cases for different $U(1)_X$ charges of the scalar particle responsible for $U(1)_X$ breaking at TeV-scale. These include the popular $U(1)_{B\text{-}L}$ and $U(1)_{R}$ models, as well as a $U(1)_C$ model which maximizes the collider signal. We numerically solve the flavored Boltzmann transport equations to calculate the total baryon asymmetry. We show that all three cases considered here can naturally explain the observed baryon asymmetry of the Universe in a large portion of the available parameter space, while satisfying the neutrino oscillation data. We find that the $U(1)_C$ case offers successful leptogenesis in a larger portion of the parameter space as compared to $U(1)_{B\text{-}L}$ and $U(1)_{R}$. We also perform a comparative study between the flavored and unflavored leptogenesis parameter space. Finally, we also study the collider prospects for all these scenarios using the lepton number violating signal of $pp\to \ell^\pm \ell^\pm+$jets mediated by the $Z'$ boson associated with $U(1)_X$. We find that HL-LHC may be able to probe a small portion of the relevant parameter space having successful leptogenesis, if neutrinos have normal mass ordering, while a $\sqrt s=100$ TeV future collider can access a much larger region of the parameter space, thereby offering an opportunity to test resonant leptogenesis in the $U(1)_X$ model.

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arXiv2024

Phenomenology of Lepton Masses and Mixing with Discrete Flavor Symmetries

The observed pattern of fermion masses and mixing is an outstanding puzzle in particle physics, generally known as the flavor problem. Over the years, guided by precision neutrino oscillation data, discrete flavor symmetries have often been used to explain the neutrino mixing parameters, which look very different from the quark sector. In this review, we discuss the application of non-Abelian finite groups to the theory of neutrino masses and mixing in the light of current and future neutrino oscillation data. We start with an overview of the neutrino mixing parameters, comparing different global fit results and limits on normal and inverted neutrino mass ordering schemes. Then, we discuss a general framework for implementing discrete family symmetries to explain neutrino masses and mixing. We discuss CP violation effects, giving an update of CP predictions for trimaximal models with nonzero reactor mixing angle and models with partial $μ-τ$ reflection symmetry, and constraining models with neutrino mass sum rules. The connection between texture zeroes and discrete symmetries is also discussed. We summarize viable higher-order groups, which can explain the observed pattern of lepton mixing where the non-zero $θ_{13}$ plays an important role. We also review the prospects of embedding finite discrete symmetries in the Grand Unified Theories and with extended Higgs fields. Models based on modular symmetry are also briefly discussed. A major part of the review is dedicated to the phenomenology of flavor symmetries and possible signatures in the current and future experiments at the intensity, energy, and cosmic frontiers. In this context, we discuss flavor symmetry implications for neutrinoless double beta decay, collider signals, leptogenesis, dark matter, as well as gravitational waves.

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arXiv2024

Probing the Sterile Neutrino Dipole Portal with SN1987A and Low-Energy Supernovae

BSM electromagnetic properties of neutrinos may lead to copious production of sterile neutrinos in the hot and dense core of a core-collapse supernova. In this work, we focus on the active-sterile transition magnetic moment portal for heavy sterile neutrinos. Firstly, we revisit the SN1987A cooling bounds for dipole portal using the integrated luminosity method, which yields more reliable results (especially in the trapping regime) compared to the previously explored via emissivity loss, aka the Raffelt criterion. Secondly, we obtain strong bounds on the dipole coupling strength reaching as low as $10^{-11} \text{ GeV}^{-1}$ from energy deposition, i.e., constrained from the observation of explosion energies of underluminous Type IIP supernovae. In addition, we find that sterile neutrino production from Primakoff upscattering off of proton dominates over scattering off of electron for low sterile neutrino masses.

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arXiv2023

Gravity-improved metastability bounds for the Type-I Seesaw Mechanism

Right-handed neutrinos (RHN) destabilize the electroweak vacuum by increasing its decay rate. In the SM, the latter is dominated by physics at the RG scale at which $λ$ reaches its minimum, $μ_*^{\text{SM}} \sim 10^{17}$ GeV. For large neutrino Yukawa coupling $Y_ν$, RHNs can push $μ_*$ beyond the Planck scale, implying that gravitational effects need to be taken into account. In this work, we perform the first comprehensive study of electroweak vacuum metastability in the type-I seesaw mechanism including these effects. Our analysis covers both low- and high-scale seesaw models, with two as well as three RHNs and for multiple values of the Higgs' non-minimal coupling to gravity. We find that gravitational effects can significantly stabilize the vacuum, leading to weaker metastability bounds. We show that metastability sets the strongest bounds for low-scale seesaws with $M_N>1$ TeV. For high-scale seesaws, we find upper bounds on the allowed masses for the RHNs, which are relevant for high-scale leptogenesis. We also point out that $\text{Tr}(Y_ν^\dagger Y_ν)$, which is commonly used to express these metastability bounds, cannot be used for all of parameter space. Instead, we argue that bounds can always be expressed reliably through $\text{Tr}(Y_ν^\dagger Y_ν\,Y_ν^\dagger Y_ν)$. Lastly, we use this insight to develop a new technique for an easier RG analysis applicable to scenarios with degenerate RHN masses.

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arXiv2023

Probing the $ν_{R}$-philic $Z'$ at DUNE near detectors

We consider a hidden $U(1)$ gauge symmetry under which only the right-handed neutrinos ($ν_{R}$) are charged. The corresponding gauge boson is referred to as the $ν_{R}$-philic $Z'$. Despite the absence of direct gauge couplings to ordinary matter at tree level, loop-induced couplings of the $ν_{R}$-philic $Z'$ via left-right neutrino mixing can be responsible for its experimental accessibility. An important feature of the $ν_{R}$-philic $Z'$ is that its couplings to neutrinos are generally much larger than its couplings to charged leptons and quarks, thus providing a particularly interesting scenario for future neutrino experiments such as DUNE to probe. We consider two approaches to probe the $ν_{R}$-philic $Z'$ at DUNE near detectors via (i) searching for $Z'$ decay signals, and (ii) precision measurement of elastic neutrino-electron scattering mediated by the $Z'$ boson. We show that the former will have sensitivity comparable to or better than previous beam dump experiments, while the latter will improve current limits substantially for large neutrino couplings.

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arXiv2022

Interplay between Resonant Leptogenesis, Neutrinoless Double Beta Decay and Collider Signals in a Model with Flavor and CP Symmetries

We present a low-scale type-I seesaw scenario with discrete flavor and CP symmetries. This scenario not only explains the measured values of the lepton mixing angles, but also makes predictions for leptonic CP violation, and connects the low-energy CP phases relevant for neutrino oscillation and neutrinoless double beta decay experiments with the high-energy CP phases relevant for leptogenesis. We show that the three right-handed Majorana neutrinos in this scenario have (almost) degenerate masses and their decays can explain the observed baryon asymmetry of the Universe via resonant leptogenesis. We study the correlation of the predicted baryon asymmetry with lepton-number-violating signals at high-energy colliders, including both prompt and displaced vertex/long-lived signatures, as well as in low-energy neutrinoless double beta decay experiments. We find that the normal ordering of light neutrino masses leads to an enhanced collider signal, whereas the neutrinoless double beta decay provides a promising probe in the inverted ordering case.

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arXiv2022

Discrete Flavor Symmetries and Lepton Masses and Mixings

We discuss neutrino mass and mixing models based on discrete flavor symmetries. These models can include a variety of new interactions and non-standard particles such as sterile neutrinos, scalar Higgs singlets and multiplets. We point at connections of the models with leptogenesis and dark matter and the ways to detect the corresponding non-standard particles at intensity and energy frontier experiments.

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arXiv2022

The Forward Physics Facility at the High-Luminosity LHC

High energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe Standard Model (SM) processes and search for physics beyond the Standard Model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF's physics potential.

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arXiv2021

How dark is the $ν_R$-philic dark photon?

We consider a generic dark photon that arises from a hidden $U(1)$ gauge symmetry imposed on right-handed neutrinos ($ν_{R}$). Such a $ν_{R}$-philic dark photon is naturally dark due to the absence of tree-level couplings to normal matter. However, loop-induced couplings to charged leptons and quarks are inevitable, provided that $ν_{R}$ mix with left-handed neutrinos via Dirac mass terms. We investigate the loop-induced couplings and find that the $ν_{R}$-philic dark photon is not inaccessibly dark, which could be of potential importance to future dark photon searches at SHiP, FASER, Belle-II, LHC 14 TeV, etc.

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