arXiv subjects

Srimoyee Sen

Publications and source records attributed to Srimoyee Sen.

At least 37 records · Page 2Linked to original sources

arXiv2023

Generalized Hall current on a finite lattice

Gapped fermion theories with gapless boundary fermions can exist in any number of dimensions. When the boundary has even space-time dimensions and hosts chiral fermions, a quantum Hall current flows from the bulk to the boundary in a background electric field. This current compensate for the boundary chiral anomaly. Such a current inflow picture is absent when the boundary theory is odd dimensional. However, in recent work, the idea of quantum Hall current has been generalized to describe odd dimensional boundary theories in continuous Euclidean space-time dimension of infinite volume. In this paper we extend this idea to a lattice regulated finite volume theory of 1+1 dimensional Wilson-Dirac fermions. This fermion theory with a domain wall in fermion mass can host gapless modes on the wall. The number of gapless fermions is equal to the integral of the divergence of the lattice generalized Hall current.

hep-th↗

arXiv2023

Index theorems, generalized Hall currents and topology for gapless defect fermions

We show how the index of the fermion operator from the Euclidean action can be used to uncover the existence of gapless modes living on defects (such as edges and vortices) in topological insulators and superconductors. The 1-loop Feynman diagram that computes the index reveals an analog of the Quantum Hall current flowing on and off the defect -- even in systems without conserved currents or chiral anomalies -- and makes explicit the interplay between topology in momentum and coordinate space. We provide several explicit examples.

cond-mat.mes-hall↗

arXiv2023

Generalized Hall currents in topological insulators and superconductors

We generalize the idea of the quantized Hall current to count gapless edge states in topological materials, applying equally well to theories in different dimensions, with or without continuous symmetries in the bulk or chiral anomalies on the boundaries. This current is related to the index of the Euclidean fermion operator and can be calculated via one-loop Feynman diagrams. Quantization of the current is shown to be governed by topology in phase space, and the procedure can be applied to topological classes governed by either ${\mathbb Z}$ or ${\mathbb Z}_2$ invariants. We analyze several explicit examples of free fermions in relativistic field theories. We speculate that it may be possible to extend the technique to interacting theories as well, such as the interesting cases where interactions gap the edge states.

cond-mat.str-el↗

arXiv2022

Long Range Plan: Dense matter theory for heavy-ion collisions and neutron stars

Since the release of the 2015 Long Range Plan in Nuclear Physics, major events have occurred that reshaped our understanding of quantum chromodynamics (QCD) and nuclear matter at large densities, in and out of equilibrium. The US nuclear community has an opportunity to capitalize on advances in astrophysical observations and nuclear experiments and engage in an interdisciplinary effort in the theory of dense baryonic matter that connects low- and high-energy nuclear physics, astrophysics, gravitational waves physics, and data science

nucl-th↗

arXiv2022

Energy conservation and axion back-reaction in a magnetic field

Axion clumps in an external magnetic field can emit electromagnetic radiation which causes them to decay. In the presence of a plasma, such radiation can become resonant if the clump frequency matches the plasma frequency. Typically, the decay or back-reaction of the clump is ignored in the literature when analyzing such radiation. In this paper we present a self consistent, semi-analytic approach which captures axion back-reaction using energy conservation. We find that inclusion of back-reaction changes the clump frequency over time enabling clumps with a range of different initial frequencies to become resonant at some point in their time evolution.

hep-ph↗

arXiv2022

Chiral fermions on lattice axion strings

I discretize axion string configuration coupled to a Dirac fermion, which in the continuum binds a massless chiral fermion in its core when the winding is one. I show that such a configuration can host one or more chiral fermions when regulated on the lattice. Realization of these chiral fermions relies on the presence of Wilson-like terms similar to the Wilson term used in lattice domain wall fermions. The number of chiral fermions on the string jumps as the Wilson-like parameter is varied with respect to the other mass scales in the problem. These jumps coincide with phase transitions along a two dimensional surface passing through the string's core. A one-loop Feynman diagram is used to demonstrate how anomaly inflow works in this lattice regularized theory.

hep-th↗

arXiv2022

Vortices in spin-0 superfluids carry magnetic flux

Vortices in spin-$0$ superfluids generically carry magnetic fields inside their cores, so that even neutral superfluid vortices may be thought of as magnetic flux tubes. We give a systematic analysis of this `vortex magnetic effect' using effective field theory, clarifying earlier literature on the subject. Our analysis shows that in superfluid Helium-$4$ the vortex magnetic effect may be large enough to be experimentally detectable.

cond-mat.quant-gas↗

arXiv2021

Electromagnetic radiation from axion condensates in a time dependent magnetic field

Time dependent magnetic fields can be sourced by spinning neutron stars, orbiting binaries and merging neutron stars. We consider electromagnetic radiation from axion condensates in the background of an alternating magnetic field. We find that a resonant peak in radiation can occur when the frequency of the alternating magnetic field is comparable with the axion mass scale. More interestingly, in situations where the frequency of the alternating magnetic field itself changes with time, as can be the case in binary mergers due to steady increase in orbital frequency, the resonant peak in radiation may occur for a range of axion mass scales scanned by the time-varying magnetic field frequency.

hep-ph↗

arXiv2021

Mass and radius relations of quarkyonic stars using an excluded volume model

Inspired by the excluded volume model for isospin symmetric quarkyonic matter, we construct an `excluded volume' model for a charge neutral quarkyonic phase whose hadronic sector contains only neutrons. We refer to this model as quarkyonic neutron matter. We compute the equation of state for this model and solve the Tolman-Oppenhermer-Volkoff equations to obtain mass and radius relations relevant for neutron stars. The most straightforward extension of the model for symmetric quarkyonic matter to quarkyonic neutron matter does not satisfy the mass radius constraints from neutron star measurements. However, we show that by incorporating appropriate nuclear interactions in the excluded volume model one can produce mass-radius relations that lie within the constraints obtained from gravitational waves of binary neutron star mergers and maximum mass measurements of neutron stars.

astro-ph.HE↗

arXiv2020

Higgs-confinement phase transitions with fundamental representation matter

We discuss the conditions under which Higgs and confining regimes in gauge theories with fundamental representation matter fields can be sharply distinguished. It is widely believed that these regimes are smoothly connected unless they are distinguished by the realization of global symmetries. However, we show that when a $U(1)$ global symmetry is spontaneously broken in \emph{both} the confining and Higgs regimes, the two phases can be separated by a phase boundary. The phase transition between the two regimes may be detected by a novel topological vortex order parameter. We first illustrate these ideas by explicit calculations in gauge theories in three spacetime dimensions. Then we show how our analysis generalizes to four dimensions, where it implies that nuclear matter and quark matter are sharply distinct phases of QCD with an approximate $SU(3)$ flavor symmetry.

hep-th↗

arXiv2020

Finite-Temperature Quarkyonic Matter with an Excluded Volume Model

We introduce a theoretical framework to analyze the thermal properties of a recently proposed "excluded volume" model of quarkyonic matter. This entails proposing finite temperature distribution functions and entropy functionals constrained by internal theoretical consistency. We use the formalism developed here to analyze the effect of temperature on the quark onset as a function of baryon density. We find that the baryon density at which the quarkyonic phase emerges decreases only slightly with temperature, an effect produced by large $N_c$. We furthermore find that a finite temperature increases the density of quarks produced. The framework presented here can be used to compute the equation of state of hot and dense quarkyonic matter which is of relevance to neutron star mergers.

nucl-th↗

arXiv2020

Chern insulator transitions with Wilson fermions on a hyperrectangular lattice

A $U(1)$ gauge theory coupled to a Wilson fermion on a $2+1$ dimensional cubic lattice is known to exhibit Chern insulator like topological transitions as a function of the the ratio $M/R$ where $M$ is the fermion mass and $R$ is the Wilson parameter. I show that, with $M$ and $R$ held fixed, a rectangular lattice with anisotropic lattice spacing can exhibit distinct topological phases as a function of the lattice anisotropy. As a consequence, a $2+1$ dimensional lattice theory without any domain wall in the fermion mass can still exhibit chiral edge modes on a $1+1$ dimensional defect across which lattice spacing changes abruptly. Likewise, a domain wall in the fermion mass on a uniform rectangular lattice can exhibit discrete changes in the number and chirality of zero modes as a function of lattice anisotropy. The construction presented in this paper can be generalized to higher dimensional space-time lattices.

hep-th↗

arXiv2019

Fractional quantum Hall effect in a relativistic field theory

We construct a class of 2+1 dimensional relativistic quantum field theories which exhibit the Fractional Quantum Hall Effect in the infrared, both in the continuum and on the lattice. The UV completion consists of a perturbative $U(1)\times U(1)$ gauge theory with only integer-charged fields, while the low energy spectrum consists of nontrivial topological phases supporting fractional currents, fractionally charged chiral surface modes and bulk anyonic excitations. Exotic phenomena such as a Fractional Quantum Spin Hall Effect can arise in such models.

hep-th↗

arXiv2019

Dynamical Derivation of the Momentum Space Shell Structure for Quarkyonic Matter

The phase space structure of zero temperature Quarkyonic Matter is a Fermi sphere of Quark Matter, surrounded by a shell of Nucleonic Matter. We construct a quasi particle model of Quarkyonic Matter based on the constituent quark model, where the quark and nucleon masses are related by m_Q = m_N/N_c, and N_c is the number of quark colors. The region of occupied states is for quarks k_Q < k_F/N_c, and for nucleons k_F < k_N < k_F + Δ. We first consider the general problem of Quarkyonic Matter with hard core nucleon interactions. We then specialize to a quasi-particle model where the hard core nucleon interactions are accounted for by an excluded volume. In this model, we show that the nucleonic shell forms past some critical density related to the hard core size, and for large densities becomes a thin shell. We explore the basic features of such a model, and argue this model has the semi-quantitative behaviour needed to describe neutron stars.

nucl-th↗

arXiv2019

Anyonic particle-vortex statistics and the nature of dense quark matter

We show that $\mathbb{Z}_3$-valued particle-vortex braiding phases are present in high density quark matter. Certain mesonic and baryonic excitations, in the presence of a superfluid vortex, have orbital angular momentum quantized in units of $\hbar/3$. Such non-local topological features can distinguish phases whose realizations of global symmetries, as probed by local order parameters, are identical. If $\mathbb{Z}_3$ braiding phases and angular momentum fractionalization are absent in lower density hadronic matter, as is widely expected, then the quark matter and hadronic matter regimes of dense QCD must be separated by at least one phase transition.

hep-th↗

arXiv2019

A Deeply Bound Dibaryon is Incompatible with Neutron Stars and Supernovae

We study the effect of a dibaryon, S, in the mass range 1860 MeV < m_S < 2054 MeV, which is heavy enough not to disturb the stability of nuclei and light enough to possibly be cosmologically metastable. Such a deeply bound state can act as a baryon sink in regions of high baryon density and temperature. We find that the ambient conditions encountered inside a newly born neutron star are likely to sustain a sufficient population of hyperons to ensure that a population of S dibaryons can equilibrate in less than a few seconds. This would be catastrophic for the stability of neutron stars and the observation of neutrino emission from the proto-neutron star of Supernova 1987A over ~ O(10)s. A deeply bound dibaryon is therefore incompatible with the observed supernova explosion, unless the cross section for S production is severely suppressed.

hep-ph↗

arXiv2018

Space-Time Picture of Baryon Stopping in the Color-Glass Condensate

We discuss baryon stopping in the Color Glass Condensate description of high energy scattering. We consider the scattering of a distribution of valence quarks on an ultra-relativistic sheet of colored charge. We compute the distribution of scattered quarks from a composite projectile, and calculate the baryon currents before and after the collisions and on an event by event basis. We obtain simple analytic estimates of the baryon number compression and rapidity shifts, which in the idealized case of plane wave scattering, produce results that agree with considerations of Anishetty-Koehler-McLerran.

hep-ph↗

arXiv2018

Plasma Effects on Lasing of Uniform Ultralight Axion Condensate

Lasing of ultralight axion condensate into photons can be sensitive to the presence of a background plasma owing to its coupling to electromagnetism. Such a scenario is particularly relevant for superradiant axion condensate around stellar mass black holes since the axion mass can be within a few orders of magnitude of the plasma frequency of the surrounding medium. In this paper I discuss the properties of the plasma around a black hole and analyze its effects on the lasing of a uniform axion condensate of mass of the order of the plasma frequency.

hep-ph↗