arXiv subjects

Soumya Jana

Publications and source records attributed to Soumya Jana.

35 records · Page 2Linked to original sources

arXiv2020

Constraints on ultra-light axions from compact binary systems

Ultra light particles $(m_a \sim 10^{-21}eV-10^{-22}eV)$ with axion-like couplings to other particles can be candidates for fuzzy dark matter (FDM) if the axion decay constant $f_a\sim 10^{17}GeV$. If a compact star is immersed in such a low mass axionic potential it develops a long range field outside the star. This axionic field is radiated away when the star is in a binary orbit. The orbital period of a compact binary decays mainly due to the gravitational wave radiation, which was confirmed first in the Hulse-Taylor binary pulsar. The orbital period can also decay by radiation of other light particles like axions and axion like particles(ALPs). For axionic radiation to take place, the orbital frequency of the periodic motion of the binary system should be greater than the mass of the scalar particle which can be radiated. This implies that, for most of the observed binaries, particles with mass $m_a< 10^{-19}eV$ can be radiated, which includes FDM particles. In this paper, we consider four compact binary systems: PSR J0348+0432, PSR J0737-3039, PSR J1738+0333, and PSR B1913+16 (Hulse Taylor Binary) and show that the observations of the decay in orbital period put the bound on axion decay constant, $f_a\lesssim \mathcal{O}(10^{11}GeV)$. This implies that Fuzzy Dark Matter cannot couple to gluons.

hep-ph↗

arXiv2019

Vector gauge boson radiation from compact binary systems in a gauged $L_μ-L_τ$ scenario

The orbital period of a compact binary system decays mainly due to quadrupole gravitational radiation, which agrees with the observation to within one percent. Other types of radiation such as ultralight scalar or pseudoscalar radiation, massive vector boson radiation also contribute to the decay of orbital period as long as the mass of the emitted particle is less than the orbital frequency of the compact binary system. We obtain an expression of the energy loss due to the radiation of massive vector field from the neutron star-neutron star and neutron star-white dwarf binaries. Due to large chemical potential of the degenerate electrons, neutron stars have large muon charge. We derive the energy loss due to $U(1)_{L_μ-L_τ}$ gauge boson radiation from the binaries. For the radiation of vector boson, the mass is restricted by $M_{Z^\prime}<Ω\simeq10^{-19}eV$ are the orbital frequencies of the compact star binaries. Using the formula of orbital period decay, we obtain constraints on the coupling constant of the gauge boson in the gauged $L_μ-L_τ$ theory for the four compact binary systems. For vector gauge boson muon coupling we find that for $M_{Z^\prime}<10^{-19}eV$, constraints on the coupling constant is $g<\mathcal{O}(10^{-20})$. We also obtain the exclusion plots of the massive vector proca field and the gauge field which can couple to muons.

hep-ph↗

arXiv2019

Constraints on higher curvature gravity from time delay between GW170817 and GRB 170817A

General relativity may be an effective theory with higher curvature correction terms in the action. Inclusion of these terms leads to exciting new possibilities, e.g., gravitational and electromagnetic perturbations following different geodesics; leading to a time delay. Such a time delay was observed between the gravitational wave event GW170817 and its electromagnetic counterpart GRB 170817A. We describe how this effect can be used to constrain the coupling of the higher curvature term. Our method is sufficiently general and applicable to any higher curvature theory.

gr-qc↗

arXiv2019

Constraints on $f(R)$ theories of gravity from GW170817

A novel constraint on $f(R)$ theories of gravity is obtained from the gravitational wave signal emitted from the binary neutron star merger event GW170817. The $f(R)$ theories possess an additional massive scalar degree of freedom apart from the massless spin-2 modes. The corresponding scalar field contributes an additional attractive, short-ranged "fifth" force affecting the gravitational wave radiation process. We realize that chameleon screening is necessary to conform with the observation. A model independent bound $\vert f'(R_0) -1\vert < 3\times 10^{-3}$ has been obtained, where the prime denotes the derivative with respect $R$ and $R_0$ is the curvature of our Universe at present. Though we use the nonrelativistic approximations and obtain an order of magnitude estimate of the bound, it comes from direct observations of gravitational waves and thus it is worth noting. This bound is stronger/equivalent compared to some earlier other bounds such as from the Cassini mission in the Solar-System, Supernova monopole radiation, the observed CMB spectrum, galaxy cluster density profile, etc., although it is weaker than best current constraints ($\vert f'(R_0) -1\vert \lesssim 10^{-6}$) from cosmology. Using the bound obtained, we also constrain the parameter space in the $f(R)$ theories of dark energy like Hu-Sawicki, Starobinsky, and Tsujikawa models.

gr-qc↗

arXiv2019

Overcharging black holes and cosmic censorship in Eddington-inspired Born-Infeld gravity

The Eddington-inspired Born-Infeld (EiBI) gravity is a modification of the theory of general relativity inspired by the nonlinear Born-Infeld electrodynamics. The theory is described by a series of higher curvature terms added to the Einstein-Hilbert action with the parameter $κ$. The EiBI gravity has several interesting exact neutral and charged black hole solutions. We study the problem of overcharging extremal black hole solutions of EiBI gravity using a charged test particle to create naked singularity. We show that unlike general relativity, the overcharging could be possible for a charged extremal black hole in EiBI gravity as long as the matter sector is described by usual Maxwell's electrodynamics. Once the matter sector is also modified in accordance to the Born-Infeld prescription with the parameter $b$, the overcharging is not possible as long as the parameters obey the condition $4 κb^2 \leq 1$.

gr-qc↗

arXiv2018

Constraints on Born-Infeld gravity from the speed of gravitational waves after GW170817 and GRB 170817A

The observations of gravitational waves from the binary neutron star merger event GW170817 and the subsequent observation of its electromagnetic counterparts from the gamma-ray burst GRB 170817A provide us a significant opportunity to study theories of gravity beyond general relativity. An important outcome of these observations is that they constrain the difference between the speed of gravity and the speed of light to less than $10^{-15}c$. Also, the time delay between the arrivals of gravitational waves at different detectors constrains the speed of gravity at the Earth to be in the range $0.55c < v_{gw} < 1.42c$. We use these results to constrain a widely studied modified theory of gravity: Eddington-inspired Born-Infeld (EiBI) gravity. We show that, in EiBI theory, the speed of gravitational waves in matter deviates from $c$. From the time delay in arrival of gravitational wave signals at Earth-based detectors, we obtain the bound on the theory parameter $κ$ as $\vertκ\vert \lesssim 10^{21}\, m^2$. Similarly, from the time delay between the signals of GW170817 and GRB 170817A, in a background Friedmann-Robertson-Walker universe, we obtain $\vert κ\vert \lesssim 10^{37}\, m^2$. Although the bounds on $κ$ are weak compared to other earlier bounds from the study of neutron stars, stellar evolution, primordial nucleosynthesis, etc., our bounds are from the direct observations and thus worth noting.

gr-qc↗

arXiv2017

Born-Infeld gravity with a Brans-Dicke scalar

Recently proposed Born-Infeld (BI) theories of gravity assume a constant BI parameter ($κ$). However, no clear consensus exists on the sign and value of $κ$. Recalling the Brans-Dicke (BD) approach, where a scalar field was used to generate the gravitational constant $G$, we suggest an extension of Born-Infeld gravity with a similar Brans-Dicke flavor. Thus, a new action, with $κ$ elevated to a spacetime dependent real scalar field, is proposed. We illustrate this new theory in a cosmological setting with pressureless dust and radiation as matter. Assuming a functional form of $κ(t)$, we numerically obtain the scale factor evolution and other details of the background cosmology. It is known that BI gravity differs from general relativity (GR) in the strong-field regime but reduces to GR for intermediate and weak fields. Our studies in cosmology demonstrate how, with this new, scalar-tensor BI gravity, deviations from GR as well as usual BI gravity, may arise in the weak-field regime too. For example, we note a late-time acceleration without any dark energy contribution. Apart from such qualitative differences, we note that fixing the sign and value of $κ$ is no longer a necessity in this theory, though the origin of the BD scalar does remain an open question.

gr-qc↗

arXiv2017

Dictionary-based Monitoring of Premature Ventricular Contractions: An Ultra-Low-Cost Point-of-Care Service

While cardiovascular diseases (CVDs) are prevalent across economic strata, the economically disadvantaged population is disproportionately affected due to the high cost of traditional CVD management. Accordingly, developing an ultra-low-cost alternative, affordable even to groups at the bottom of the economic pyramid, has emerged as a societal imperative. Against this backdrop, we propose an inexpensive yet accurate home-based electrocardiogram(ECG) monitoring service. Specifically, we seek to provide point-of-care monitoring of premature ventricular contractions (PVCs), high frequency of which could indicate the onset of potentially fatal arrhythmia. Note that a traditional telecardiology system acquires the ECG, transmits it to a professional diagnostic centre without processing, and nearly achieves the diagnostic accuracy of a bedside setup, albeit at high bandwidth cost. In this context, we aim at reducing cost without significantly sacrificing reliability. To this end, we develop a dictionary-based algorithm that detects with high sensitivity the anomalous beats only which are then transmitted. We further compress those transmitted beats using class-specific dictionaries subject to suitable reconstruction/diagnostic fidelity. Such a scheme would not only reduce the overall bandwidth requirement, but also localising anomalous beats, thereby reducing physicians' burden. Finally, using Monte Carlo cross validation on MIT/BIH arrhythmia database, we evaluate the performance of the proposed system. In particular, with a sensitivity target of at most one undetected PVC in one hundred beats, and a percentage root mean squared difference less than 9% (a clinically acceptable level of fidelity), we achieved about 99.15% reduction in bandwidth cost, equivalent to 118-fold savings over traditional telecardiology.

cs.LG↗

arXiv2016

Born-Infeld cosmology with scalar Born-Infeld matter

Cosmology in Eddington-inspired Born-Infeld gravity is investigated using a scalar Born-Infeld field (e.g. tachyon condensate) as matter. In this way, both in the gravity and matter sectors we have Born-Infeld-like structures characterized by their actions and via two separate constants, $κ$ and $α_T^2$ respectively. With a particular choice of the form of $\dotϕ$ (the time derivative of the Born-Infeld scalar), analytical cosmological solutions are found. Thereafter, we explore some of the unique features of the corresponding cosmological spacetimes. For $κ>0$, our solution has a de Sitter-like expansion both at early and late times, with an intermediate deceleration sandwiched between the accelerating phases. On the other hand, when $κ<0$, the initial de Sitter phase is replaced by a bounce. Our solutions, at late time, fit well with available supernova data-- a fact we demonstrate explicitly. The estimated properties of the Universe obtained from the fitting of the $κ>0$ solution, are as good as in $Λ$CDM cosmology. However, the $κ<0$ solution has to be discarded due to the occurrence of a bounce at an unacceptably low redshift.

gr-qc↗

arXiv2015

Euclidean Auto Calibration of Camera Networks: Baseline Constraint Removes Scale Ambiguity

Metric auto calibration of a camera network from multiple views has been reported by several authors. Resulting 3D reconstruction recovers shape faithfully, but not scale. However, preservation of scale becomes critical in applications, such as multi-party telepresence, where multiple 3D scenes need to be fused into a single coordinate system. In this context, we propose a camera network configuration that includes a stereo pair with known baseline separation, and analytically demonstrate Euclidean auto calibration of such network under mild conditions. Further, we experimentally validate our theory using a four-camera network. Importantly, our method not only recovers scale, but also compares favorably with the well known Zhang and Pollefeys methods in terms of shape recovery.

cs.CV↗

arXiv2015

Born-Infeld gravity coupled to Born-Infeld electrodynamics

We investigate spherically symmetric, static spacetimes in Eddington-inspired Born-Infeld gravity coupled to Born-Infeld electrodynamics. The two constants, $b^2$ and $κ$ which parametrise the Born-Infeld structures in the electrodynamics (matter) and gravity sectors, characterise the features of our analytical solutions. Black holes or naked singularities are found to arise, depending on the values of $b^2$ and $κ$, as well as charge and mass. Several such solutions are classified and understood through the analysis of the associated metric functions for fixed $κ$, varying $b^2$ and vice-versa. Further, we also compare the new metric functions with those for the known $b^2\rightarrow \infty$ (Maxwell) and the $κ\rightarrow 0$ (geonic black hole) cases. Interestingly, for a particular relation between these two parameters, $b^2=1/{4κ},\, κ>0$, we obtain a solution resembling the well-known Reissner-Nordstr\" om line element, albeit some modifications. Using this particular solution as the background spacetime, we study null geodesics for Born-Infeld photons and also, gravitational lensing. Among interesting features we note $(i)$ an increase in the radius of the photon sphere with increasing $κ$ and $(ii)$ a net positive contribution in the leading order correction term involving $κ$, in the weak lensing formula for the deflection angle. We also investigate the effective potential and light propagation for various other solutions through numerics and plots. In summary, our work is the first attempt towards figuring out how Born-Infeld structures in both the matter and gravity sectors can influence the nature and character of resulting gravitational fields.

gr-qc↗

arXiv2014

Cosmology in a reduced Born-Infeld--$f(T)$ theory of gravity

A perfect fluid, spatially flat cosmology in a $f(T)$ model, derived from a recently proposed general Born-Infeld type theory of gravity is studied. Four dimensional cosmological solutions are obtained assuming the equation of state $p=ωρ$. For a positive value of $λ$ (a parameter in the theory) the solution is singular (of big-bang type) but may have accelerated expansion at an early stage. For $λ<0$ there exists a non-zero minimum scale factor and a finite maximum value of the energy density, but the curvature scalar diverges. Interestingly, for $λ<0$, the universe may undergo an eternal accelerated expansion with a de Sitter expansion phase at late times. We find these features without considering any extra matter field or even negative pressure. Fitting our model with Supernova data we find that the simplest dust model ($p=0$), with $λ>0$, is able to generate acceleration and fits well, although the resulting properties of the universe differ much from the known, present day, accepted values. The best fit model requires (with $λ> 0$) an additional component of the physical matter density, with a negative value of the equation of state parameter, along with dust. The $λ< 0$ solutions do not fit well with observations. Though these models do not explain the dark energy problem with consistency, their analysis does shed light on the plausibility of an alternative geometrical explanation.

gr-qc↗

arXiv2013

Three dimensional Eddington--inspired Born--Infeld gravity: solutions

Three dimensional Eddington-inspired Born--Infeld gravity is studied with the goal of finding new solutions. Beginning with cosmology, we obtain analytical and numerical solutions for the scale factor, a(t), in spatially flat (k=0) and spatially curved (k=+1,-1) Friedmann-Roberston-Walker universes with (i) pressureless dust (P=0) and (ii) perfect fluid (P=ρ/2), as matter sources. When the theory parameter κ>0, our cosmological solutions are generically singular (except for the open universe, with a specific condition). On the other hand, for κ<0 we do find non-singular cosmologies. We then move on towards finding static, circularly symmetric line elements with matter obeying (i) p=0 and (ii) p=ρ/2. For p=0, the solution found is nonsingular for κ<0 with the matter--stress--energy representing inhomogeneous dust. For p=ρ/2 we obtain nonsingular solutions, for all κ, and discuss some interesting characteristics of these solutions. Finally, we look at the rather simple p=-ρcase where the solutions are either de Sitter or anti-de Sitter or flat spacetime.

gr-qc↗

arXiv2012

Perturbative stability of catenoidal soap films

The perturbative stability of catenoidal soap films formed between parallel, equal radii, coaxial rings is studied using analytical and semi-analytical methods. Using a theorem on the nature of eigenvalues for a class of Sturm--Liouville operators, we show that for the given boundary conditions, azimuthally asymmetric perturbations are stable, while symmetric perturbations lead to an instability--a result demonstrated in Ben Amar et. al [7] using numerics and experiment. Further, we show how to obtain the lowest real eigenvalue of perturbations, using the semi-analytical Asymptotic Iteration Method (AIM). Conclusions using AIM support the analytically obtained result as well as the results in [7]. Finally, we compute the eigenfunctions and show, pictorially, how the perturbed soap film evolves in time.

physics.class-ph↗

arXiv2008

Alphabet Sizes of Auxiliary Variables in Canonical Inner Bounds

Alphabet size of auxiliary random variables in our canonical description is derived. Our analysis improves upon estimates known in special cases, and generalizes to an arbitrary multiterminal setup. The salient steps include decomposition of constituent rate polytopes into orthants, translation of a hyperplane till it becomes tangent to the achievable region at an extreme point, and derivation of minimum auxiliary alphabet sizes based on Caratheodory's theorem.

cs.IT↗

arXiv2005

Unified Theory of Source Coding: Part I -- Two Terminal Problems

Since the publication of Shannon's theory of one terminal source coding, a number of interesting extensions have been derived by researchers such as Slepian-Wolf, Wyner, Ahlswede-Körner, Wyner-Ziv and Berger-Yeung. Specifically, the achievable rate or rate-distortion region has been described by a first order information-theoretic functional of the source statistics in each of the above cases. At the same time several problems have also remained unsolved. Notable two terminal examples include the joint distortion problem, where both sources are reconstructed under a combined distortion criterion, as well as the partial side information problem, where one source is reconstructed under a distortion criterion using information about the other (side information) available at a certain rate (partially). In this paper we solve both of these open problems. Specifically, we give an infinite order description of the achievable rate-distortion region in each case. In our analysis we set the above problems in a general framework and formulate a unified methodology that solves not only the problems at hand but any two terminal problem with noncooperative encoding. The key to such unification is held by a fundamental source coding principle which we derive by extending the typicality arguments of Shannon and Wyner-Ziv. Finally, we demonstrate the expansive scope of our technique by re-deriving known coding theorems. We shall observe that our infinite order descriptions simplify to the expected first order in the known special cases.

cs.IT↗

arXiv2005

Unified Theory of Source Coding: Part II -- Multiterminal Problems

In the first paper of this two part communication, we solved in a unified framework a variety of two terminal source coding problems with noncooperative encoders, thereby consolidating works of Shannon, Slepian-Wolf, Wyner, Ahlswede-Körner, Wyner-Ziv, Berger {\em et al.} and Berger-Yeung. To achieve such unification we made use of a fundamental principle that dissociates bulk of the analysis from the distortion criterion at hand (if any) and extends the typicality arguments of Shannon and Wyner-Ziv. In this second paper, we generalize the fundamental principle for any number of sources and on its basis exhaustively solve all multiterminal source coding problems with noncooperative encoders and one decoder. The distortion criteria, when applicable, are required to apply to single letters and be bounded. Our analysis includes cases where side information is, respectively, partially available, completely available and altogether unavailable at the decoder. As seen in our first paper, the achievable regions permit infinite order information-theoretic descriptions. We also show that the entropy-constrained multiterminal estimation problem can be solved as a special case of our theory.

cs.IT↗