arXiv subjects

Subhendra Mohanty

Publications and source records attributed to Subhendra Mohanty.

At least 19 recordsLinked to original sources

arXiv2026

Determination of the Angular Momentum of Radiated Gravitons, Scalars, and Dark Photons from Binary Orbits

We compute the energy and angular momentum radiated by compact binaries through gravitational waves, scalar and vector fields, using the field-theoretic approach. We observe that each emitted graviton carries away an angular momentum of $\dot{J}/\dot {N}\simeq 2\hbar$, not only for elliptical orbits (as has already been pointed out by Page [arXiv:2409.00305]) but also for hyperbolic orbits. We extend the analysis to scalar and vector radiation and find that the angular momentum carried by each emitted quantum of radiation is approximately $\hbar$, i.e., $\dot{J}/\dot{N}\simeq \hbar$ for both types of radiation. We demonstrate that the radiated energy and angular momentum of binary systems can be determined from the evolution of the orbital angular frequency and the eccentricity of the quasi-Kepler orbit. However, a gauge-invariant decomposition of the angular momentum carried by the emitted particles into the spin and orbital components is not possible.

gr-qc↗

arXiv2026

Gravitational waves from parabolic encounters: A study of linear and nonlinear memory

The memory effect is known to introduce a permanent displacement in the gravitational wave (GW) detectors after the passage of a GW signal. While the $\textit{linear memory}$ adheres to the source properties, the $\textit{non-linear memory}$ is a secondary effect sourced by the GW itself. In the present work, we discuss GW signals with both these kinds of memory effects, while focusing on the parabolic limit of an encounter. This special case is theoretically intriguing and emerges as a limiting situation for both eccentric and hyperbolic events. However, in this paper, we argue that a simple extrapolation of memory calculations for eccentric or hyperbolic cases to the parabolic case may lead to incorrect estimations. Therefore, we treat the parabola as a special case and use an intrinsic parameterization, with which we calculate gravitational wave signals and their energy spectrum via an effective field theory formalism. Unlike the hyperbolic case, which is known to have linear memory, we notice that parabolic encounters bring out new features in the zero frequency limit (ZFL). The exactly parabolic case is studied here primarily as an idealized separatrix between bound and unbound motion, and our analysis highlights some of the key challenges and salient aspects of GW memory in this regime.

gr-qc↗

arXiv2026

Background Fields Meet the Heat Kernel: Gauge Invariance and RGEs without diagrams

We introduce a new method that exploits the combination of the Heat Kernel (HK) and Background Field Method to compute gauge-invariant and gauge parameter-independent quantities such as the effective potential, anomalous dimensions, and renormalization group equations. In contrast to currently employed techniques, these results are obtained exclusively from the dynamics of the background fields, without relying on supplementary input from, e.g., traditional diagrammatic calculations. This is achieved by a consistent treatment of open and closed derivatives in the HK expansions. In this way, we compute the standard quantities such as $β$ functions and their gauge-parameter independence when background fields are on-shell. We demonstrate this formalism for instructive examples such as Scalar QED and Yukawa theory. Full results for the bosonic part of the Standard Model provide further validation of our approach.

hep-th↗

arXiv2026

Testing the Starobinsky model of inflation with resonant cavities

We show that the Starobinsky inflation model based on $R^2$ gravity has a special feature that it provides a unique scalaron-two-graviton vertex with a coupling proportional to $1/M_P$. In this model stochastic gravitational waves are produced when the scalaron - which is the massive scalar mode of the metric - decays into gravitons during reheating. This decay is accompanied by decay of scalaron into matter as well through a similar coupling, providing an efficient reheating. The stochastic gravitational waves thus produced have characteristic strain $h_c\sim 10^{-35}-10^{-34}$ in the frequency range $10^{6}-10^{12}\, {\rm Hz}$ which makes them accessible to resonant cavity searches for graviton to photon conversions. The detection of these high frequency gravitational waves would be a significant step in experimentally testing the Starobinsky inflation model.

gr-qc↗

arXiv2026

Limits on the axion-photon coupling from Chandrayaan-2 observations

Axions and axion-like particles (ALPs) have gained immense attention in searches for beyond Standard Model (BSM) physics. Experiments searching for axions leverage their predicted couplings to Standard Model (SM) particles to look for observable signals. Though weak, these couplings allow axions to be produced abundantly in the interiors of stars such as the Sun. Once created, axions can escape the Sun and while passing through the solar atmosphere, oscillate into photons in the magnetic field producing x-rays. For the first time, we used data from the observation of soft x-rays from the quiet Sun during the 2019-20 solar minimum by the solar x-ray monitor (XSM), onboard India's Chandrayaan-2 lunar exploration mission, to constrain the coupling of axions to photons ($g_{a γγ}$). Using the latest models of the solar atmosphere to calculate the magnetic field and plasma frequency, we constrain $g_{a γγ} \lesssim (0.50 - 2.26) \times 10^{-10}$ GeV$^{-1}$ at $95\%$ confidence level for axion masses $m_a \lesssim 5 \times 10^{-4}$eV.

hep-ph↗

arXiv2025

Detection of Axion Stars in Galactic Magnetic Fields

We perform a linear mode analysis of a uniformly distributed cloud of axion-like particles (ALPs) embedded in a magnetized intergalactic medium, in order to investigate the stability of axion stars under realistic astrophysical conditions. We find that when the frequency $ω$ of transverse waves is much smaller than the collision frequency $ν_c$ of the intergalactic plasma, the conversion of ALPs into photons occurs on timescales far longer than the age of the Universe, ensuring stability of the star. In the opposite regime, $ω\gg ν_c$, significant axion-to-photon conversion may occur if the condition $\tfrac{β^2}{m_a^2-ω_p^2} < 1$ is satisfied, where $β$ depends on the ALP--photon coupling and the magnetic field, $m_a$ is the ALP mass, and $ω_p$ is the plasma frequency. We have calculated up to second order in perturbations to compute the effect of an ALP star. Since the calculated value of parameter $β^2$ is extremely small in comparison with $ω^2_p$, we argue that the direct detection of an axion star is highly unlikely in experiments like NCLE. However, since the calculated $β$ is extremely small compared to $ω_p$, this requires an unrealistically fine-tuned coincidence between $m_a$ and $ω_p$. As a consequence we argue that that detection of Our results therefore suggest that axion stars remain stable in typical intergalactic environments, though extreme magnetic fields (e.g.\ near magnetars) may lead to different outcomes.

astro-ph.CO↗

arXiv2025

Gauge Choices, Infrared Pitfalls, and Thermal Effects in Effective Potentials

The evaluation of effective potentials is critical for a range of phenomenological applications, including inflation, vacuum stability, and phase transitions. A drawback arises from the gauge-dependence of the effective potential. Furthermore, in theories with spontaneous symmetry breaking, the effective potential exhibits infrared (IR) divergences in the limit of vanishing Goldstone masses. By considering the multiplicative anomaly that arises due to non-factorisation of elliptic operators in the Fermi gauge when computing the effective potential at one-loop order, we demonstrate that its gauge independence and IR behaviour are improved to the corresponding findings of Landau gauge calculations simultaneously. The latter are straightforwardly and transparently reproduced using an approach that employs the Heat Kernel technique, thereby providing a shortcut to reflect anomaly-related cancellations from the outset. Our findings generalise to the treatment of the effective potential at finite temperature. In particular, the Heat Kernel extends gauge independence to any value of the expansion in mass over temperature.

hep-th↗

arXiv2025

A White Paper on The Multi-Messenger Science Landscape in India

The multi-messenger science using different observational windows to the Universe such as Gravitational Waves (GWs), Electromagnetic Waves (EMs), Cosmic Rays (CRs), and Neutrinos offer an opportunity to study from the scale of a neutron star to cosmological scales over a large cosmic time. At the smallest scales, we can explore the structure of the neutron star and the different energetics involved in the transition of a pre-merger neutron star to a post-merger neutron star. This will open up a window to study the properties of matter in extreme conditions and a guaranteed discovery space. On the other hand, at the largest cosmological scales, multi-messenger observations allow us to study the long-standing problems in physical cosmology related to the Hubble constant, dark matter, and dark energy by mapping the expansion history of the Universe using GW sources. Moreover, the multi-messenger studies of astrophysical systems such as white dwarfs, neutron stars, and black holes of different masses, all the way up to a high redshift Universe, will bring insightful understanding into the physical processes associated with them that are inaccessible otherwise. This white paper discusses the key cases in the domain of multi-messenger astronomy and the role of observatories in India which can explore uncharted territories and open discovery spaces in different branches of physics ranging from nuclear physics to astrophysics.

astro-ph.HE↗

arXiv2025

One Loop Thermal Effective Action

We compute the one loop effective action for a Quantum Field Theory at finite temperature, in the presence of background gauge fields, employing the Heat-Kernel method. This method enables us to compute the thermal corrections to the Wilson coefficients associated with effective operators up to arbitrary mass dimension, which emerge after integrating out heavy scalars and fermions from a generic UV theory. The Heat-Kernel coefficients are functions of non-zero background `electric', `magnetic' fields, and Polyakov loops. A major application of our formalism is the calculation of the finite temperature Coleman-Weinberg potential in effective theories, necessary for the study of phase transitions. A novel feature of this work is the systematic calculation of the dependence of Polyakov loops on the thermal factors of Heat-Kernel coefficients and the Coleman-Weinberg potential. We study the effect of Polyakov loop factors on phase transitions and comment on future directions in applications of the results derived in this work.

hep-th↗

arXiv2025

Gauge Invariant Effective Potential

We show that the long-standing problem of gauge dependence of the effective potential arises due to the factorisation of the determinant of operators, which is invalid when we take the zeta-regularised trace of the operators. We show by correcting for this assumption by computing the multiplicative anomaly, the gauge-dependent terms of the effective potential cancel. We also show that in two- and odd-dimensional non-compact spacetime manifolds where the multiplicative anomaly term is zero, the standard calculation of one-loop effective potential gives a gauge-independent result. These results are in support of our claim that the multiplicative anomaly may play a crucial role in removing the gauge dependence in the effective potential in the four-dimensional non-compact manifold. Noting the non-trivial aspects of this anomaly computation for a generic scenario, we propose the Heat-Kernel method to compute the effective potential where this anomaly emerges as a total derivative, thus redundant. We explicitly show how one can calculate the gauge independent, effective action and the Coleman-Weinberg effective potential by employing the Heat-Kernel method. Based on this result, we advocate the Heat-Kernel expansion as the most straightforward method, as it naturally deals with the matrix elliptic operator for the calculation of manifestly gauge independent, effective actions compared to other conventional methods.

hep-th↗

arXiv2025

Gravitational radiation from binary systems in Unimodular gravity

Unimodular gravity (UG) is classically considered identical to General Relativity (GR). However, due to restricted diffeomorphism symmetry, the Bianchi identites do not lead to the conservation of energy-momentum tensor. Thus, the conservation of energy-momentum tensor needs to be separately assumed in order to reconcile with GR. Relaxing this assumption, one finds that the conservation violation can lead to differences with GR, which can be subsequently examined in astrophysical and cosmological scenarios. To this end, we examine the predictions of UG in the context of binary systems emitting gravitational radiation. Primarily, we show how the field equations involve a diffusion function which quantifies the measure of non-conservation. Due to this violation, the dispersion relation is modified. Incorporating these changes, we provide an expression for the energy loss by the binaries, which reduces to Peters-Mathews result in the GR limit. Using binary pulsar data, we constrain the theory parameter $ζ$ (which signifies non-conservation) by determining the rate of orbital decay. The strongest constrain on $ζ$ comes out to be $\vert ζ\vert \leq 5\times 10^{-4}$ which is better by an order of magnitude than an existing equivalent constraint coming from the tidal deformability of the neutron stars.

gr-qc↗

arXiv2024

Ultra-light dark matter explanation of NANOGrav observations

The angular correlation of pulsar residuals observed by NANOGrav and other pulsar timing array (PTA) collaborations show evidence in support of the Hellings-Downs correlation expected from stochastic gravitational wave background (SGWB). In this paper, we offer a non-gravitational wave explanation of the observed pulsar timing correlations as caused by an ultra-light $L_μ - L_τ$ gauge boson dark matter (ULDM). ULDM can affect the pulsar correlations in two ways. The gravitational potential of vector ULDM gives rise to a Shapiro time delay of the pulsar signals and a non-trivial angular correlation (as compared to the scalar ULDM case). In addition, if the pulsars have a non-zero charge of the dark matter gauge group, then the electric field of the local dark matter causes an oscillation of the pulsar and a corresponding Doppler shift of the pulsar signal. We point out that pulsars carry a significant charge of muons, and thus the $L_μ - L_τ$ vector dark matter contributes to both the Doppler oscillations and the time delay of the pulsar signals. The synergy between these two effects provides a better fit to the shape of the angular correlation function, as observed by the NANOGrav collaboration, compared to the standard SGWB explanation or the SGWB combined with time delay explanations. Our analysis shows that in addition to the SGWB signal, there may potentially be excess timing residuals attributable to the $L_μ - L_τ$ ULDM.

hep-ph↗

arXiv2024

Gravitational memory signal from neutrino self-interactions in supernova

Neutrinos with large self-interactions, arising from exchange of light scalars or vectors with mass $M_ϕ\simeq 10{\rm MeV}$, can play a useful role in cosmology for structure formation and solving the Hubble tension. It has been proposed that large self-interactions of neutrinos may change the observed properties of supernova like the neutrino luminosity or the duration of the neutrino burst. In this paper, we study the gravitational wave memory signal arising from supernova neutrinos. Our results reveal that memory signal for self-interacting neutrinos are weaker than free-streaming neutrinos in the high frequency range. Implications for detecting and differentiating between such signals for planned space-borne detectors, DECIGO and BBO, are also discussed.

gr-qc↗

arXiv2024

Open EFT treatment of Inflation with Thermal Initial Conditions

Investigating the thermal inflationary model, we introduce stochastic effects, incorporating a cutoff parameter $σ$ which distinguishes between quantum and classical modes. Testing the model against Planck 2018 data, we observe a preference for a non-zero $σ$ at least at 68\% C.L., suggesting the classicalization of most modes and providing a theoretical foundation for the quantum to classical transition. As a result of introducing the stochastic effects, we find that the solution to the large-scale power deficit requires a lower comoving temperature of inflaton.

gr-qc↗

arXiv2024

Frequency space derivation of linear and non-linear memory gravitational wave signals from eccentric binary orbits

The memory effect in gravitational wave (GW) signals is the phenomenon, wherein the relative position of two inertial GW detectors undergoes a permanent displacement owing to the passage of GWs through them. Measurement of the memory signal is an important target for future observations as it establishes a connection between observations with field-theoretic results like the soft-graviton theorems. Theoretically, the memory signal is predicted at the leading order quadrupole formula for sources like binaries in hyperbolic orbits. This can be in the realm of observations by Advanced LIGO, Einstein-Telescope, or LISA for black-holes with masses $\sim$ $O(10^3 \, M_\odot$) scattered by the super-massive black-hole at the galactic center. Apart from the direct memory component there is a non-linear memory signal in the secondary GW emitted from the primary GW chirp-signals emitted by coalescing binaries. In this paper, we compute the gravitational wave signals and their energy spectrum using the field-theoretic method by computing the scattering amplitudes for eccentric elliptical and hyperbolic binary orbits. The field theoretic calculation gives us the gravitational waveforms of linear and non-linear memory signals directly in the frequency space. The frequency domain templates are useful for extracting signals from the data. We compare our results with other calculations of linear and non-linear memory signals in literature and point out novel features we find in our calculations like the presence of $\log(ω)$ terms in the linear memory from hyperbolic orbits.

gr-qc↗

arXiv2023

Gravitational radiation from binary systems in $f(R)$ gravity: A semi-classical approach

The rate of energy loss and orbital period decay of quasi-stable compact binary systems are derived in $f(R)$ theory of gravity using the method of a single vertex graviton emission process from a classical source. After linearising the $f(R)$ action written in an equivalent scalar-tensor format in the Einstein frame, we identify the appropriate interaction terms between the massless spin-2 tensor mode, massive scalar mode, and the energy momentum tensor. The definition of the scalar field is related to the $f(R)$ models. Then using the interaction vertex we compute the rate of energy loss due to spin-2 quadrupole radiation, which comes out to be the same as the Peter-Mathews formula with a multiplication factor, and also the energy loss due to the scalar dipole radiation. The total energy loss is the sum of these two contributions. Our derivation is most general as it is applicable for both arbitrary eccentricity of the binary orbits and arbitrary mass of the scalar field. Using the derived theoretical formula for the period decay of the binary systems, we compare the predictions of $f(R)$ gravity and general relativity for the observations of four binary systems, i.e. Hulse-Taylor Binary, PSR J1141-6545, PSR J1738+0333, and PSR J0348+0432. Thus we put bound on three well-known $f(R)$ dark energy models, namely the Hu-Sawicki, the Starobinsky, and the Tsujikawa model. We get the best constraint on $f'(R_0)-1$ (where $R_0$ is the scalar curvature of the Universe at the present epoch) from the Tsujikawa model, i.e $\vert f'(R_0)-1\vert < 2.09\times 10^{-4}$. This bound is stronger than those from most of the astrophysical observations and even some cosmological observations.

gr-qc↗

arXiv2022

Flavour specific neutrino self-interaction: $H_0$ tension and IceCube

Self-interaction in the active neutrinos is studied in the literature to alleviate the $H_0$ tension. Similar self-interaction can also explain the observed dips in the flux of the neutrinos coming from the distant astro-physical sources in IceCube detectors. In contrast to the flavour universal neutrino interaction considered for solving the $H_0$ tension, which is ruled out from particle physics experiments, we consider flavour specific neutrino interactions. We show that the values of self-interaction coupling constant and mediator mass required for explaining the IceCube dips are inconsistent with the strong neutrino self-interactions preferred by the combination of BAO, HST and Planck data. However, the required amount of self-interaction between tau neutrinos ($ν_τ$) in inverted hierarchy for explaining IceCube dips is consistent with the moderate self-interaction region of cosmological bounds at 1-$σ$ level. For the case of other interactions and hierarchies, the IceCube preferred amount of self-interaction is consistent with moderate self-interaction region of cosmological bounds at 2-$σ$ level only.

hep-ph↗

arXiv2022

Gravitational radiation from binary systems in massive graviton theories

Theories with massive gravitons have peculiarity called the van Dam-Veltman-Zakharov discontinuity in that the massive theory propagator does not go to the massless graviton propagator in the zero graviton mass limit. This results in large deviation in Newtons law for massive graviton theories even when the graviton mass vanishes. We test the vDVZ in massive graviton theories for single graviton vertex process namely the gravitational radiation from a classical source. We calculate the gravitational radiation from compact binaries using the perturbative Feynman diagram method. We perform this calculation for Einstein's gravity with massless gravitons and verify that the Feynman diagram calculation reproduces the quadrupole formula. Using the same procedure we calculate the gravitational radiation for three massive graviton theories: (1) the Fierz-Pauli theory (2) the modified Fierz-Pauli theory without the vDVZ discontinuity and (3) the Dvali-Gabadadze-Porrati theory with a momentum dependent graviton mass. We put limits on the graviton mass in each of these theories from observations of binary pulsar timings.

gr-qc↗