arXiv subjects

Amit Bhoonah

Publications and source records attributed to Amit Bhoonah.

At least 19 recordsLinked to original sources

arXiv2026

Spin Correlation and Quantum Entanglement of Fermion Pairs in Transversely Polarized $e^-e^+$ Collisions

We systematically study the spin correlations and quantum entanglement in transversely polarized electron-positron collisions. We find that the $s$-channel QED process $e^-e^+\to f\bar f$ produces a maximally entangled state in the entire phase space when the initial beams are transversely polarized, while the quantum magic varies in different phase space points for the maximally entangled Bell states. For electroweak processes, the spin configuration of final states depends on chiral couplings, and the entanglement is also greatly enhanced by transverse polarization as in the QED process. For Bhabha scattering with additional $t$-channel contributions, the transverse polarization still increases the final state entanglement, although with some dilution. The sensitive dependence of final spin states on the transverse polarization makes the beam polarization a powerful tool for generating and controlling quantum entanglement in collider experiments, opening up new opportunities for quantum information studies at high-energy colliders.

hep-ph↗

arXiv2026

The NANOGrav 15 yr Data Set: Piecewise Power-Law Reconstruction of the Gravitational-Wave Background

The NANOGrav 15-year (NG15) data set provides evidence for a gravitational-wave background (GWB) signal at nanohertz frequencies, which is expected to originate either from a cosmic population of inspiraling supermassive black-hole binaries or new particle physics in the early Universe. A firm identification of the source of the NG15 signal requires an accurate reconstruction of its frequency spectrum. In this paper, we provide such a spectral characterization of the NG15 signal based on a piecewise power-law (PPL) ansatz that strikes a balance between existing alternatives in the literature. Our PPL reconstruction is more flexible than the standard constant-power-law model, which describes the GWB spectrum in terms of only two parameters: an amplitude A and a spectral index gamma. Concurrently, it better approximates physically realistic GWB spectra -- especially those of cosmological origin -- than the free spectral model, since the latter allows for arbitrary variations in the GWB amplitude from one frequency bin to the next. Our PPL reconstruction of the NG15 signal relies on individual PPL models with a fixed number of internal nodes (i.e., constant power law, broken power law, doubly broken power law, etc.) that are ultimately combined in a Bayesian model average. The data products resulting from our analysis provide the basis for fast refits of spectral GWB models.

astro-ph.HE↗

arXiv2025

Galactic magnetic fields seeded by ultralight dark photons

In this work, we show that ultralight dark photons, which couple to the Standard Model photon through kinetic mixing, can potentially source galactic scale magnetic fields. Although these magnetic fields would be too weak to detect at present in galaxies due to plasma screening effects, we show that dark photons can provide the seed magnetic field strength ($10^{-20}$ G) required for dynamo amplification in galaxies. Such dynamo-amplified magnetic fields are consistent with observations of $\mu$G strength galactic magnetic fields.

hep-ph↗

arXiv2025

A Baryon and Lepton Number Violation Model Testable at the LHC

Proton decay experiments typically constrain baryon number violation to the scale of grand unified theories. From a phenomenological point of view, this makes direct probing of the associated new resonances, such as the X and Y bosons, out of reach for even the most optimistic future experiments. It has, however, been known that certain specific patterns of baryon and lepton number violation can suppress proton decay by multiple powers of the masses of the heavy resonances involved, opening the possibility that the observed limits on the proton lifetime are consistent with baryon number violating physics at energy scales much lower than that of grand unification. We construct an explicit example of such a model which violates baryon number by one unit, $\Delta \text{B} = -1$, and lepton number by three units, $\Delta \text{L} = -3$, and show that despite stringent limits on the predicted $p \rightarrow e^{+}/\mu^{+} \overline{\nu}\overline{\nu}$ mode from the Super-Kamiokande experiment, the masses of the newly introduced elementary particles can be $\mathcal{O}$(TeV). We identify interesting unique signatures of baryon number violation of this model that can be probed both with currently available LHC data and with the upcoming High-Luminosity LHC. We also present a scenario for low-scale baryogenesis within the framework of this model.

hep-ph↗

arXiv2025

Sub-MHz Radio Background from Ultralight Dark Photon Dark Matter

Dark photons are a well-motivated candidate for dark matter, but their detection becomes challenging for ultralight masses with both experimental and astrophysical probes. In this work, we propose a new approach to explore this regime through the dark inverse Compton scattering of ultralight dark photons with cosmic ray electrons and positrons. We show this process generates a potentially observable background radiation that is most prominent at frequencies below MHz. We compute this effect using the latest cosmic ray models and radio absorption maps. Comparing it to observations of the Milky Way's radio spectrum from Explorer 43, Radio Astronomy Explorer 2, and the Parker Solar Probe, we place leading constraints on the kinetic mixing of dark photon dark matter for masses $\lesssim 2 \times 10^{-17} \ \rm eV$.

hep-ph↗

arXiv2024

Right-Handed Neutrino Masses from the Electroweak Scale

Heavy right-handed neutrinos are highly motivated due to their connection with the origin of neutrino masses via the seesaw mechanism. If the right-handed neutrino Majorana mass is at or below the weak scale, direct experimental discovery of these states is possible in laboratory experiments. However, there is no a priori basis to expect right-handed neutrinos to be so light since the Majorana mass is a technically natural parameter and could comfortably reside at any scale, including at scales far above the weak scale. Here we explore the possibility that the right-handed neutrino Majorana mass originates from electroweak symmetry breaking. Working within an effective theory with two Higgs doublets, nonzero lepton number is assigned to the bilinear operator built from the two Higgs fields, which is then coupled to the right-handed neutrino mass operator. In tandem with the neutrino Yukawa coupling, following electroweak symmetry breaking a seesaw mechanism operates, generating the light SM neutrino masses along with right-handed neutrinos with masses below the electroweak scale. This scenario leads to novel phenomenology in the Higgs sector, which may be probed at the LHC and at future colliders. There are also interesting prospects for neutrinoless double beta decay and lepton flavor violation. We also explore some theoretical aspects of the scenario, including the technical naturalness of the effective field theory and ultraviolet completions of the right-handed neutrino Majorana mass.

hep-ph↗

arXiv2023

Laboratory constraints on ultralight axion-like particles from precision atomic spectroscopy

Ultralight bosonic dark matter has come under increasing scrutiny as a dark matter candidate that has the potential to resolve puzzles in astronomical observation. We demonstrate that high-precision measurements of time variation in the frequency ratios of atomic transitions achieves leading sensitivity to ultralight axion-like particle dark matter at low masses. These bounds are the first laboratory-based bounds on this class of dark matter models. We propose further measurements that could enhance sensitivity to ultralight axion-like particles.

hep-ph↗

arXiv2023

Axion Electrodyanmics in the Presence of Current Sources

Axions are among the most sought-after candidates for dark matter. In the ultralight regime, they could help alleviate puzzles in small scale cosmology. Searches for a halo of axion dark matter rely on the electromagnetic response to a magnetic field. In this work, we resolve a number of issues in the determination of this response by carefully solving Maxwell's equations in the presence of an axion background. We find that the electric field induced by a magnetic field in an axion background is significant and unsuppressed by the size of the experiment.

hep-ph↗

arXiv2023

Detecting axion dark matter with Rydberg atoms via induced electric dipole transitions

Long-standing efforts to detect axions are driven by two compelling prospects, naturally accounting for the absence of charge-conjugation and parity symmetry breaking in quantum chromodynamics, and for the elusive dark matter at ultralight mass scale. Many experiments use advanced cavity resonator setups to probe the magnetic-field-mediated conversion of axions to photons. Here, we show how to search for axion matter without relying on such a cavity setup, which opens a new path for the detection of ultralight axions, where cavity based setups are infeasible. When applied to Rydberg atoms, which feature particularly large transition dipole elements, this effect promises an outstanding sensitivity for detecting ultralight dark matter. Our estimates show that it can provide laboratory constraints in parameter space that so far had only been probed astrophysically, and cover new unprobed regions of parameter space. The Rydberg atomic gases offer a flexible and inexpensive experimental platform that can operate at room temperature. We project the sensitivity by quantizing the axion-modified Maxwell equations to accurately describe atoms and molecules as quantum sensors wherever axion dark matter is present.

hep-ph↗

arXiv2023

Probing Exotic Phases Via Stochastic Gravitational Wave Spectra

Stochastic backgrounds of gravitational waves (GWs) from the pre-BBN era offer a unique opportunity to probe the universe beyond what has already been achieved with the Cosmic Microwave Background (CMB). If the source is short in duration, the low frequency tail of the resulting GW spectrum follows a universal frequency scaling dependent on the equation of state of the universe when modes enter the horizon. We demonstrate that the distortion of the equation of state due to massive particles becoming non-relativistic can lead to an observable dip in the GW spectrum. To illustrate this effect, we consider a first order chiral symmetry breaking phase transition in the weak-confined Standard Model (WCSM). The model features a large number of pions and mostly elementary fermions with masses just below the critical temperature for the phase transition. These states lead to a 20$\%$ dip in the GW power. We find potential sensitivity to the distortions in the spectrum to future GW detectors such as LISA, DECIGO, BBO, and $μ$Ares.

hep-ph↗

arXiv2022

Diffuse X-Ray and Gamma-Ray Limits on Boson Stars that Interact with Nuclei

Light bosonic dark matter can form gravitationally bound states known as boson stars. In this work, we explore a new signature of these objects interacting with the interstellar medium (ISM). We show how small effective couplings between the bosonic dark matter and the nucleon lead to a potential that accelerates ISM baryons as they transit the boson star, making the ISM within radiate at a high rate and energy. The low ISM density, however, implies the majority of Galactic boson stars will be too faint to be observable through this effect. By contrast, the diffuse photon flux, in hard x-rays and soft gamma-rays, produced by boson stars interacting with the ionized ISM phases can be sizable. We compute this diffuse flux and compare it to existing observations from HEAO-1, INTEGRAL and COMPTEL to infer limits on the fraction of these objects. This novel method places constraints on boson star dark matter while avoiding back-action effects from ambient baryons on the boson star configuration, unlike terrestrial searches where it has been noted that back-action can screen light bosonic fields. In addition, this study could be extended to other couplings and structures formed from light dark matter. For dark matter masses $(10^{-14}$, $10^{-8}) \ {\rm eV}$ and boson star masses $(10^{-10}$, $10^{-1}) \ M_{\odot}$, we find the constraints on the fraction can go down to $f_* \lesssim 10^{-9}$ for dark matter in boson stars that is directly coupled to the Standard Model.

hep-ph↗

arXiv2021

Gravitational Waves From Dark Sectors, Oscillating Inflatons, and Mass Boosted Dark Matter

Gravitational waves signatures from dynamical scalar field configurations provide a compelling observational window on the early universe. Here we identify intriguing connections between dark matter and scalars fields that emit gravitational waves, either through a first order phase transition or oscillating after inflation. To study gravitational waves from first order phase transitions, we investigate a simplified model consisting of a heavy scalar coupled to a vector and fermion field. We then compute gravitational wave spectra sourced by inflaton field configurations oscillating after E-Model and T-Model inflation. Some of these gravitational wave signatures can be uncovered by the future Big Bang Observatory, although in general we find that MHz-GHz frequency gravitational wave sensitivity will be critical for discovering the heaviest dark sectors. Intriguingly, we find that scalars undergoing phase transitions, along with E-Model and T-Model potentials, can impel a late-time dark matter mass boost and generate up to Planck mass dark matter. For phase transitions and oscillating inflatons, the largest dark matter mass boosts correspond to higher amplitude stochastic gravitational wave backgrounds.

hep-ph↗

arXiv2021

Detecting Composite Dark Matter with Long Range and Contact Interactions in Gas Clouds

Cold interstellar gas clouds provide an exciting new method to discover dark matter. Their immense size makes them uniquely sensitive to interactions from the heaviest, most rarefied dark matter models. Using gas cloud observations, we derive constraints on heavy composite dark matter coupled to the Standard Model through a light dark photon for dark matter up to a thousand solar masses. We find gas clouds are also sensitive to very large composite dark matter that interacts with nuclei through a fixed contact interaction cross section. We also study the contact interaction model and implement multiscatter and overburden analyses to obtain bounds from experiments like CDMS, CRESST, DAMA, XQC, and XENON1T.

hep-ph↗

arXiv2021

Etching Plastic Searches for Dark Matter

Large panels of etched plastic, situated aboard the Skylab Space Station and inside the Ohya quarry near Tokyo, have been used to set limits on fluxes of cosmogenic particles. These plastic particle track detectors also provide the best sensitivity for some heavy dark matter that interacts strongly with nuclei. We revisit prior dark matter bounds from Skylab, and incorporate geometry-dependent thresholds, a halo velocity distribution, and a complete accounting of observed through-going particle fluxes. These considerations reduce the Skylab bound's mass range by a few orders of magnitude. However, a new analysis of Ohya data covers a portion of the prior Skylab bound, and excludes dark matter masses up to the Planck mass. Prospects for future etched plastic dark matter searches are discussed.

hep-ph↗

arXiv2020

Superradiant Searches for Dark Photons in Two Stage Atomic Transitions

We study a new mechanism to discover dark photon fields, by resonantly triggering two photon transitions in cold gas preparations. Using coherently prepared cold parahydrogen, coupling sensitivity for sub-meV mass dark photon fields can be advanced by orders of magnitude, with a modified light-shining-through-wall setup. We calculate the effect of a background dark photon field on the dipole moment and corresponding transition rate of cold parahydrogen pumped into its first vibrational excited state by counter-propagating laser beams. The nonlinear amplification of two photon emission triggered by dark photons in a cold parahydrogen sample is numerically simulated to obtain the expected dark photon coupling sensitivity.

hep-ph↗

arXiv2019

Galactic Center Gas Clouds and Novel Bounds on Ultra-Light Dark Photon, Vector Portal, Strongly Interacting, Composite, and Super-Heavy Dark Matter

Cold gas clouds recently discovered hundreds of parsecs from the center of the Milky Way Galaxy have the potential to detect dark matter. With a detailed treatment of gas cloud microphysical interactions, we determine Galactic Center gas cloud temperatures, free electron abundances, atomic ionization fractions, heating rates, cooling rates, and find how these quantities vary with metallicity. Considering a number of different dark sector heating mechanisms, we set new bounds on ultra-light dark photon dark matter for masses $10^{-22}-10^{-10}$ eV, vector portal dark matter coupled through a sub-MeV mass boson, and up to $10^{60}$ GeV mass dark matter that interacts with baryons.

hep-ph↗

arXiv2019

Gravitational fermion creation during an anisotropic phase of cosmological expansion

The free Dirac equation is solved in a Bianchi Type I space-time, which represents a homogeneous but anisotropic universe, to show the creation of fermionic particles. It is found that unlike in the isotropic case, massless fermion production is possible. An estimate of the energy density of massless particles created during an early anisotropic phase of cosmological expansion is shown to cause substantial back-reaction on the gravitational field. The potential relevance to dark matter particle production, primordial magnetogenesis, and early universe cosmology is discussed briefly.

gr-qc↗

arXiv2018

Calorimetric Dark Matter Detection With Galactic Center Gas Clouds

We demonstrate that dark matter heating of gas clouds hundreds of parsecs from the Milky Way Galactic center provides a powerful new test of dark matter interactions. To illustrate, we set a leading bound on nucleon scattering for 10-100 MeV mass dark matter. We also constrain millicharged dark matter models, including those proposed to match the recent EDGES 21 cm absorption anomaly. For Galactic center gas clouds, galactic fields' magnetic deflection of electromagnetically charged dark matter is mitigated, because the magnetic fields around the Galactic center are poloidal, as opposed to being aligned parallel to the Milky Way disk. We discuss prospects for detecting dark matter using a population of Galactic center gas clouds warmed by dark matter.

hep-ph↗