arXiv subjects

Hemant Prajapati

Publications and source records attributed to Hemant Prajapati.

6 recordsLinked to original sources

arXiv2026

Flavor specific chiral $U(1)_X$ framework for explaining the ATOMKI anomaly

Recent anomalies in nuclear transitions observed by the ATOMKI Collaboration suggest the existence of a new boson with a mass of $\sim 17$ MeV. A theoretically consistent interpretation requires a framework that not only matches the kinematics but also reproduces the observed decay rates while satisfying stringent experimental constraints. Among various possibilities, an axial-vector or mixed vector--axial-vector mediator $Z'$ emerges as the most viable candidate. However, getting such couplings for a light $Z'$ gauge boson is a highly nontrivial task. In this work, we construct a gauged chiral, flavor specific $U(1)_X$ extensions of the Standard Model where the associated $Z'$ boson acts as the $17$ MeV particle. By employing a two Higgs doublet framework, we generate the necessary nonvanishing axial-vector couplings while ensuring gauge anomaly cancellation and consistent fermion mass generation. Focusing on the $^8\mathrm{Be}$ and $^4\mathrm{He}$ signals, we show that in this model the viable parameter space to resolve the ATOMKI anomalies is also consistent with a diverse set of experimental constraints, including atomic parity violation, beam dump experiments, meson decays, and neutrino nucleus and neutrino electron scatterings. Our results demonstrate that this framework offers a theoretically sound and phenomenologically robust solution to the ATOMKI anomaly.

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arXiv2024

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

Coherent elastic neutrino-nucleus (CE$\nu$NS) and elastic neutrino-electron scattering (E$\nu$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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arXiv2024

Dark hyperCharge Symmetry

We introduce a new class of $U(1)_X$ symmetries where all Standard Model fermions are ``chiral," i.e., the left- and right-handed components have different charges under the $U(1)_X$ symmetry. Gauge anomaly cancellation is achieved by introducing three Standard Model gauge singlet dark fermions ($f^i$; $i=1,2,3$) charged under this symmetry. We systematically present chiral solutions for cases in which (a) one, (b) two, or (c) all three generations of Standard Model fermions are charged under the $U(1)_X$ symmetry. The $U(1)_X$ charges of these dark fermions are uniquely determined by anomaly cancellation conditions. These new fermions belong to the dark sector, with the lightest of them being a good dark matter candidate. Additionally, the $Z'$ gauge boson mediates interactions between the dark and visible sectors, and we call this $U(1)_X$ symmetry as the ``dark hyperCharge" symmetry. Using a benchmark model, we explore phenomenological implications in the heavy $Z'$ case ($M_{Z'} > M_Z$), analyzing collider constraints and examining the lightest dark fermion's viability as dark matter. Our analysis shows that it satisfies all current dark matter constraints over a wide range of dark matter mass.

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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

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

$B-L$ model in light of the CDF II result

Recent CDF II collaboration's result on $W$ mass measurements contradict Standard Model prediction, requiring new physics to explain this anomaly. Such new physics may manifest through tree-level or loop-level corrections to the mass of the $W$ boson. In this work, we investigate the possibility that the CDF-II result is indicative of new physics not directly changing the $W$ boson mass but rather the $Z$ boson mass. Since the $Z$ boson mass goes as an input into the Standard Model prediction for $W$ boson mass, this change in $Z$ mass ultimately leads to the discrepancy between the CDF-II measurement and the Standard Model expectation. We demonstrate this idea through one of the simplest and most studied $U(1)$ gauge extensions of the Standard Model, namely the gauged $U(1)_{B-L}$ extension. We demonstrate that $B-L$ extended models can explain the revised best-fit values for $S$, $T$, and $U$ following the CDF II results. We studied the parameter space of models with and without mixing between neutral gauge bosons. We also reviewed the dark matter constraints and demonstrated that there is parameter space that is compatible with the current $W$ boson mass, relic abundance, and direct detection experiments.

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