arXiv subjects

Rahul Srivastava

Publications and source records attributed to Rahul Srivastava.

At least 37 records · Page 2Linked to original sources

arXiv2025

Constraining low scale dark hypercharge symmetry at spallation, reactor and Dark Matter direct detection experiments

Coherent elastic neutrino-nucleus (CE$ν$NS) and elastic neutrino-electron scattering (E$ν$ES) data are exploited to constrain ``chiral'' $U(1)_{X}$ gauged models with light vector mediator mass. These models fall under a distinct class of new symmetries called dark hypercharge symmetries. A key feature is the fact that the $Z'$ boson can couple to all Standard Model fermions at tree level, with the $U(1)_X$ charges determined by the requirement of anomaly cancellation. Notably, the charges of leptons and quarks can differ significantly depending on the specific anomaly cancellation solution. As a result, different models exhibit distinct phenomenological signatures and can be constrained through various experiments. In this work, we analyze the recent data from the COHERENT experiment, along with results from dark matter (DM) direct detection experiments such as XENONnT, LUX-ZEPLIN, and PandaX-4T, and place new constraints on three benchmark models. Additionally, we set constraints from a performed analysis of TEXONO data and discuss the prospects of improvement in view of the next-generation DM direct detection DARWIN experiment.

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arXiv2025

Comprehensive Phenomenology of the Dirac Scotogenic Model: Novel Low Mass Dark Matter

The Dirac Scotogenic model provides an elegant mechanism for generating small Dirac neutrino masses at the one-loop level. A single abelian discrete $Z_{6}$ symmetry simultaneously protects the ``Diracness'' of the neutrinos and the stability of the dark matter candidate. This symmetry originates as an unbroken subgroup of the so-called 445 $U(1)_{B-L}$ symmetry. Here, we thoroughly explore the phenomenological implications of this construction, including an analysis of electroweak vacuum stability, charged lepton flavor violation, and the dark matter phenomenology. After considering all constraints, we also show that the model allows for the possibility of novel low-mass scalar and fermionic dark matter, a feature not shared by its canonical Majorana counterpart.

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arXiv2025

Probing Standard Model and Beyond with Reactor CE$ν$NS Data of CONUS+ experiment

We explore the potential of reactor antineutrino-induced Coherent Elastic Neutrino-Nucleus Scattering (CE$ν$NS) data from the CONUS+ experiment to investigate both the Standard Model (SM) and Beyond Standard Model (BSM) scenarios. Alongside CE$ν$NS, Elastic Neutrino-Electron Scattering (E$ν$ES) events are also included in our analysis, enabling more stringent constraints on new physics. Within the SM, we examine the weak mixing angle as a precision test of the electroweak sector. For BSM scenarios, we constrain the parameter space of light mediators arising from neutrino generalized interactions (NGI), while also setting limits on the electromagnetic properties of neutrinos, including their charge radius, millicharge, and magnetic moment.

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arXiv2024

Large lepton number violation at colliders: predictions from the minimal linear seesaw mechanism

Small neutrino masses can be sourced by a tiny vacuum expectation value of a leptophilic Higgs doublet, and mediated by Quasi-Dirac heavy neutrinos. In such simplest linear seesaw picture the neutrino mass mediators can be accessible to colliders. We describe novel charged Higgs and heavy neutrino production mechanisms that can be sizeable at $e^+ e^-$, $e^- γ$, $pp$, or muon colliders and discuss some of the associated signatures. The oscillation length of the heavy neutrino mediators is directly related to the light neutrino mass ordering. Moreover, lepton number violation can be large despite the smallness of neutrino masses, and may shed light on the Majorana nature of neutrinos and the significance of basic symmetries in weak interaction.

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arXiv2024

Dark Matter Escaping Direct Detection Runs into Higgs Mass Hierarchy Problem

The current generation of Dark Matter Direct Detection Experiments has ruled out a large region of parameter space for dark matter, particularly in the ($10 - 1000$) GeV mass range. However, due to very low event rates, searching for dark matter in the heavy mass range, $\mathcal{O}$(TeV), is a daunting task requiring even larger volume detectors and long exposure times. We show that for a broad class of dark matter models of the type that these experiments are searching, including some of the most popular candidates, the heavy dark matter mass range can be ruled out in its entirety once we take into account the large corrections to Higgs mass imparted by such heavy dark matter. We show that such a limit is applicable to all types of dark matter i.e. scalar, vector, and fermionic, provided they couple directly with Higgs. By taking some simple and well studied dark matter models we show that the latest LZ limits can completely rule out such a dark matter except in a narrow range around $M_h/2$ mass.

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arXiv2024

Cutting the Scotogenic loop: Adding flavor to Dark Matter

We introduce a framework for hybrid neutrino mass generation, wherein scotogenic dark sector particles, including dark matter, are charged non-trivially under the $A_4$ flavor symmetry. The spontaneous breaking of the $A_4$ group to residual $\mathcal{Z}_2$ subgroup results in the ``cutting" of the radiative loop. As a consequence the neutrinos acquire mass through the hybrid ``scoto-seesaw" mass mechanism, combining aspects of both the tree-level seesaw and one-loop scotogenic mechanisms, with the residual $\mathcal{Z}_2$ subgroup ensuring the stability of the dark matter. The flavor symmetry also leads to several predictions including the normal ordering of neutrino masses and ``generalized $μ-τ$ reflection symmetry" in leptonic mixing. Additionally, it gives testable predictions for neutrinoless double beta decay and a lower limit on the lightest neutrino mass. Finally, $A_4 \to \mathcal{Z}_2$ breaking also leaves its imprint on the dark sector and ties it with the neutrino masses and mixing. The model allows only scalar dark matter, whose mass has a theoretical upper limit of $\lesssim$ 600 GeV, with viable parameter space satisfying all dark matter constraints, available only up to about 80 GeV. Conversely, fermionic dark matter is excluded due to constraints from the neutrino sector. Various aspects of this highly predictive framework can be tested in both current and upcoming neutrino and dark matter experiments.

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arXiv2024

Hubble Tension and Cosmological Imprints of $U(1)_X$ Gauge Symmetry: $U(1)_{B_3-3 L_i}$ as a case study

The current upper limit on $N_{\rm eff}$ at the time of CMB by Planck 2018 can place stringent constraints in the parameter space of BSM paradigms where their additional interactions may affect neutrino decoupling. Motivated by this fact in this paper we explore the consequences of light gauge boson ($Z'$) emerging from local $U(1)_X$ symmetry in $N_{\rm eff}$ at the time of CMB. First, we analyze the generic $U(1)_X$ models with arbitrary charge assignments for the SM fermions and show that, in the context of $N_{\rm eff}$ the generic $U(1)_X$ gauged models can be broadly classified into two categories, depending on the charge assignments of first generation leptons. We then perform a detailed analysis with two specific $U(1)_X$ models: $U(1)_{B_3-3L_e}$ and $U(1)_{B_3-3L_μ}$ and explore the contribution in $N_{\rm eff}$ due to the presence of $Z'$ realized in those models. For comparison, we also showcase the constraints from low energy experiments like: Borexino, Xenon 1T, neutrino trident, etc. We show that in a specific parameter space, particularly in the low mass region of $Z'$, the bound from $N_{\rm eff}$ (Planck 2018) is more stringent than the experimental constraints. Additionally, a part of the regions of the same parameter space may also relax the $H_0$ tension.

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arXiv2024

The $N_{\rm eff}$ at CMB challenges $U(1)_X$ light gauge boson scenarios

The relativistic degrees of freedom ($N_{\rm eff}$) is one of the crucial cosmological parameters. The precise measurement of $N_{\rm eff}$ at the time of cosmic microwave background formation, by Planck 2018 can be used to understand the new fundamental interactions, in particular involving light mediators. Presence of any new particle with sufficient energy density and sizeable interactions with Standard Model particles at the temperature around $\sim$ MeV can significantly alter the neutrino decoupling and hence $N_{\rm eff}$. Thus the bound on $N_{\rm eff}$ can place stringent constraints on various beyond Standard Model paradigms involving light particles. $U(1)_X$ models are among such scenarios and are widely studied in several aspects. In this work, we consider several popular $U(1)_X$ models with light $Z'$ boson like $U(1)_{B-L}$, $U(1)_{B - 3L_i}$, $U(1)_{B_i - 3 L_j}$, $U(1)_{L_i - L_j}$; $i,j =1,2,3$ being the flavour indices and study their impact on $N_{\rm eff}$. We also examine the constraints from ground based experiments like Xenon1T, Borexino, trident, etc. Our analysis shows that for light mass $M_{Z'} \lesssim \mathcal{O} (\rm{MeV})$ the $N_{\rm eff}$ provides the most stringent constraints on the $Z'$ mass and coupling, far exceeding the existing constraints from other experiments.

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arXiv2024

Predictions from scoto-seesaw with $A_4$ modular symmetry

This paper's novelty lies in introducing a hybrid scoto-seesaw model rooted in $A_4$ discrete modular symmetry leading to several interesting phenomenological implications. The scoto-seesaw framework leads to generation of one mass square difference $( Δm^2_{\rm atm}$) using the type-I seesaw mechanism at the tree level. Additionally, the scotogenic contribution is vital in obtaining the other mass square difference ($Δm^2 _{\rm sol}$) at the loop level, thus providing a clear interpretation of the two different mass square differences. The non-trivial transformation of Yukawa couplings under the $A_4$ modular symmetry helps to explore neutrino phenomenology with a specific flavor structure of the mass matrix. In addition to predictions for neutrino mass ordering, mixing angles and CP phases, this setup leads to precise predictions for $\sum m_i$ as well as $|m_{ee}|$. In particular, the model predicts $\sum m_i \in (0.073,0.097)$ eV and $\left| m_{ee}\right| \in (3.15,6.66)\times 10^{-3} $ eV range; within reach of upcoming experiments. Furthermore, our model is also promising for addressing lepton flavor violations, i.e., $\ell_α\to \ell_βγ$, $\ell_α\to 3\ell_β$ and $μ- e $ conversion rates while staying within the realm of current experimental limits.

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arXiv2024

Can Leptonic Mixing Matrix have a Wolfenstein Form?

We analyze the possibility of the leptonic mixing matrix having a Wolfenstein form at the Grand Unified Theory scale. The renormalization group evolution of masses and mixing angles from the high scale to electroweak scale, in certain new physics scenarios, can significantly alter the form of the leptonic mixing matrix. In the past it was shown that such significant enhancement implies that the leptonic mixing matrix at high scale can be the same or similar in structure to the quark one. We thoroughly analyze this hypothesis in the light of the latest neutrino oscillation data as well as other constraints such as those coming from neutrinoless double beta decay. We show that such an ansatz, at least within the context of minimal supersymmetric models, is no longer compatible with the latest experimental data.

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arXiv2024

XENONnT and LUX-ZEPLIN constraints on DSNB-boosted dark matter

We consider a scenario in which dark matter particles are accelerated to semi-relativistic velocities through their scattering with the Diffuse Supernova Neutrino Background. Such a subdominant, but more energetic dark matter component can be then detected via its scattering on the electrons and nucleons inside direct detection experiments. This opens up the possibility to probe the sub-GeV mass range, a region of parameter space that is usually not accessible at such facilities. We analyze current data from the XENONnT and LUX-ZEPLIN experiments and we obtain novel constraints on the scattering cross sections of sub-GeV boosted dark matter with both nucleons and electrons. We also highlight the importance of carefully taking into account Earth's attenuation effects as well as the finite nuclear size into the analysis. By comparing our results to other existing constraints, we show that these effects lead to improved and more robust constraints.

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arXiv2024

Neutrino Mass Sum Rules from Modular $\mathcal{A}_4$ Symmetry

Modular symmetries offer a dynamic approach to understanding the flavour structure of leptonic mixing. Using the modular $\mathcal{A}_4$ flavour symmetry integrated in a type-II seesaw, we propose a simple and minimalistic model that restricts the neutrino oscillation parameter space and, most importantly, introduces a sum rule in the physical neutrino masses. When combined with the mass squared differences observed in neutrino oscillations, this sum rule determines the absolute neutrino mass scale. This has significant implications for cosmology, neutrinoless double beta decay experiments and direct neutrino mass measurements. In particular, the model predicts $\sum_i m_i \approx 0.1$ eV for both normal and inverted ordering, and thus can be fully probed by the current generation of cosmological probes in the upcoming years.

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arXiv2023

CDF-II $W$ Boson Mass Anomaly in the Canonical Scotogenic Neutrino-Dark Matter Model

The CDF-II collaboration's recent high-precision measurement of $W$ boson mass indicates new physics contribution(s) beyond the Standard Model. We investigate the possibility of the well-known canonical Scotogenic model to explain the CDF-II measurement. The Scotogenic model is a popular scenario beyond the Standard Model that induces neutrino masses at the 1-loop level and includes a viable dark matter candidate, either scalar or fermionic. For both scalar and fermionic dark matter possibilities, we simultaneously examine the constraints coming from (a) neutrino mass, oscillation, neutrinoless double beta decay and lepton flavour violation experiments, (b) from LEP and LHC (c) from dark matter relic density and direct detection experiments (d) from the oblique $S,T,U$ parameter values consistent with CDF-II $W$ boson measurement. We demonstrate that the new CDF-II measurement rules out the feasible parameter space of the scalar dark matter in the high mass regions ($m_{η_{R}} \gtrsim 500~\text{GeV}$), while still allowing the intermediate mass regions $54~\text{GeV} \lesssim m_{η_{R}} \lesssim 76~\text{GeV}$. We also showed that the fermionic dark matter candidate in the canonical Scotogenic model, in the range $M_{N_{1}} \lesssim 500~\text{GeV} $ , can simultaneously explain all the aforementioned issues. Furthermore, we investigated how the recent findings from ATLAS 2023 impact this study.

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arXiv2023

Phenomenology of the simplest linear seesaw mechanism

The linear seesaw mechanism provides a simple way to generate neutrino masses. In addition to Standard Model particles, it includes quasi-Dirac leptons as neutrino mass mediators, and a leptophilic scalar doublet seeding small neutrino masses. Here we review its associated physics, including restrictions from theory and phenomenology. The model yields potentially detectable $μ\to eγ$ rates as well as distinctive signatures in the production and decay of heavy neutrinos ($N_i$) and the charged Higgs boson ($H^\pm$) arising from the second scalar doublet. We have found that production processes such as $e^+e^-\to NN$, $e^-γ\to NH^-$ and $e^+ e^-\to H^+ H^-$ followed by the decay chain $H^\pm\to\ell_i^\pm N$, $N\to \ell_j^{\pm}W^\mp$ leads to striking lepton number violation signatures at high energies which may probe the Majorana nature of neutrinos.

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arXiv2023

Implications of first LZ and XENONnT results: A comparative study of neutrino properties and light mediators

Next generation direct dark matter detection experiments are favorable facilities to probe neutrino properties and light mediators beyond the Standard Model. We explore the implications of the recent data reported by LUX-ZEPLIN (LZ) and XENONnT collaborations on electromagnetic neutrino interactions and neutrino generalized interactions (NGIs). We show that XENONnT places the most stringent upper limits on the effective and transition neutrino magnetic moment (of the order of few $\times 10^{-12}~μ_B$) as well as stringent constraints to neutrino millicharge (of the order of $\sim 10^{-13}~e$)--competitive to LZ--and improved by about one order of magnitude in comparison to existing constraints coming from Borexino and TEXONO. We furthermore explore the XENONnT and LZ sensitivities to simplified models with light NGIs and find improved constraints in comparison to those extracted from Borexino-Phase II data.

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arXiv2023

CDF-II W boson mass in the Dirac Scotogenic model

The Dirac scotogenic model provides an elegant mechanism which explains small Dirac neutrino masses and neutrino mixing, with a single symmetry simultaneously protecting the ``Diracness'' of the neutrinos and the stability of the dark matter candidate. Here we explore the phenomenological implications of the recent CDF-II measurement of the $W$ boson mass in the Dirac scotogenic framework. We show that, in the scenario where the dark matter is mainly a $SU(2)_L$ scalar doublet, it cannot concurrently satisfy: (a) the dark matter relic density (b) the $m_W$ anomaly and (c) the direct detection constraints. However, unlike the Majorana scotogenic model, the Dirac version also has a ``dark sector'' $SU(2)_L$ singlet scalar. We show that if the singlet scalar is the lightest dark sector particle i.e. the dark matter, then all neutrino physics and dark matter constraints along with the constraints from oblique $S$, $T$ and $U$ parameters can be concurrently satisfied for $W$ boson mass in CDF-II mass range.

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arXiv2022

Physics implications of recent Dresden-II reactor data

Prompted by the recent Dresden-II reactor data we examine its implications for the determination of the weak mixing angle, paying attention to the effect of the quenching function. We also determine the resulting constraints on the unitarity of the neutrino mixing matrix, as well as on the most general type of nonstandard neutral-current neutrino interactions.

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arXiv2022

W-mass Anomaly in the Simplest Linear Seesaw Mechanism

The simplest linear seesaw mechanism can accommodate the new CDF-II $W$ mass measurement. In addition to Standard Model particles, the model includes quasi-Dirac leptons, and a second, leptophilic, scalar doublet seeding small neutrino masses. Our proposal is consistent with electroweak precision tests, neutrino physics, rare decays and collider restrictions, requiring a new charged scalar below a few TeV, split in mass from the new degenerate scalar and pseudoscalar neutral Higgs bosons.

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