Showing papers by "Tata Institute of Fundamental Research published in 2022"
TL;DR: In this article, it was shown that a copy of all the information on a Cauchy slice is also available near the boundary of the slice, leading to the information paradox.
49 citations
TL;DR: In this article , the effect of the X-ray heating of the intergalactic medium on these constraints, and also use the full shape of the 21-cm absorption feature in their inference.
Abstract: Abstract Using the global 21-cm signal measurement by the EDGES collaboration, we derive constraints on the fraction of the dark matter that is in the form of primordial black holes (PBHs) with masses in the range 10 15 –10 17 g. Improving upon previous analyses, we consider the effect of the X-ray heating of the intergalactic medium on these constraints, and also use the full shape of the 21-cm absorption feature in our inference. In order to account for the anomalously deep absorption amplitude, we also consider an excess radio background motivated by LWA1 and ARCADE2 observations. Because the heating rate induced by PBH evaporation evolves slowly, the data favour a scenario in which PBH-induced heating is accompanied by X-ray heating. Also, for the same reason, using the full measurement across the EDGES observation band yields much stronger constraints on PBHs than just the redshift of absorption. We find that 21-cm observations exclude f PBH ≳ 10 -9.7 at 95% CL for M PBH = 10 15 g. This limit weakens approximately as M 4 PBH towards higher masses, thus providing the strongest constraints on ultralight evaporating PBHs as dark matter over the entire mass range 10 15 –10 17 g. Under the assumption of a simple spherical gravitational collapse based on the Press-Schechter formalism, we also derive bounds on the curvature power spectrum at extremely small scales ( k ∼ 10 15 Mpc -1 ). This highlights the usefulness of global 21-cm measurements, including non-detections, across wide frequency bands for probing exotic physical processes.
29 citations
TL;DR: In this article , a state-of-the-art review of the fascinating world of KTaO3 (KTO) has been presented, focusing on the remarkable progress made, particularly in the last five years, particularly during the discovery of 2D electron gas trapped at the interfaces of KTO-based heterostructures.
Abstract: Long after the heady days of high-temperature superconductivity, the oxides came back into the limelight in 2004 with the discovery of the 2D electron gas (2DEG) in SrTiO3 (STO) and several heterostructures based on it. Not only do these materials exhibit interesting physics, but they have also opened up new vistas in oxide electronics and spintronics. However, much of the attention has recently shifted to KTaO3 (KTO), a material with all the "good" properties of STO (simple cubic structure, high mobility, etc.) but with the additional advantage of a much larger spin-orbit coupling. In this state-of-the-art review of the fascinating world of KTO, it is attempted to cover the remarkable progress made, particularly in the last five years. Certain unsolved issues are also indicated, while suggesting future research directions as well as potential applications. The range of physical phenomena associated with the 2DEG trapped at the interfaces of KTO-based heterostructures include spin polarization, superconductivity, quantum oscillations in the magnetoresistance, spin-polarized electron transport, persistent photocurrent, Rashba effect, topological Hall effect, and inverse Edelstein Effect. It is aimed to discuss, on a single platform, the various fabrication techniques, the exciting physical properties and future application possibilities of this family of materials.
25 citations
TL;DR: In this article , it was shown that for collective instability to occur, the difference of momentum distributions of two flavors must change sign, i.e., there is a zero crossing, and this necessary criterion is valid for Hamiltonian flavor evolution of ultrarelativistic standard model neutrino occupation matrices.
Abstract: Neutrinos in supernovae, neutron stars, and in the early Universe may change flavor collectively and unstably, due to neutrino-neutrino forward scattering. We prove that, for collective instability to occur, the difference of momentum distributions of two flavors must change sign, i.e., there is a zero crossing. This necessary criterion, which unifies slow and fast instabilities, is valid for Hamiltonian flavor evolution of ultrarelativistic standard model neutrino occupation matrices, including damping due to collisions in the relaxation approximation. It provides a simple but rigorous condition for collective flavor transformations that are believed to be important for stellar dynamics, nucleosynthesis, and neutrino phenomenology.
20 citations
TL;DR: In this article , a perturbative version of holography for theories of gravity coupled to matter in AdS spacetime is presented. But it is not a holographic model.
Abstract: In a theory of quantum gravity, states can be represented as wavefunctionals that assign an amplitude to a given configuration of matter fields and the metric on a spatial slice. These wavefunctionals must obey a set of constraints as a consequence of the diffeomorphism invariance of the theory, the most important of which is known as the Wheeler-DeWitt equation. We study these constraints perturbatively by expanding them to leading nontrivial order in Newton's constant about a background AdS spacetime. We show that, even within perturbation theory, any wavefunctional that solves these constraints must have specific correlations between a component of the metric at infinity and energetic excitations of matter fields or transverse-traceless gravitons. These correlations disallow strictly localized excitations. We prove perturbatively that two states or two density matrices that coincide at the boundary for an infinitesimal interval of time must coincide everywhere in the bulk. This analysis establishes a perturbative version of holography for theories of gravity coupled to matter in AdS.
15 citations
TL;DR: In this article , a short-time octonion linear canonical transform (STOLCT) was proposed to generate a new transform called 3D-short-time linear canonical transformation (3D-STLCT).
13 citations
TL;DR: In this paper , a semi-numerical code for ReionIzation with PhoTon Conservation (script) is presented, which computes the large-scale temperature and ionized hydrogen fields in a cosmologically representative volume accounting for the patchiness in these quantities arising from reionization.
Abstract: ABSTRACT The ionization and thermal state of the intergalactic medium (IGM) during the epoch of reionization has been of interest in recent times because of their close connection to the first stars. We present in this paper a seminumerical code which computes the large-scale temperature and ionized hydrogen fields in a cosmologically representative volume accounting for the patchiness in these quantities arising from reionization. The code is an extension to a previously developed version for studying the growth of ionized regions, namely, Semi Numerical Code for ReionIzation with PhoTon Conservation (script). The main additions in the present version are the inhomogeneous recombinations which are essential for temperature calculations. This extended version of script also implements physical consequences of photoheating during reionization, e.g. radiative feedback. These enhancements allow us to predict observables which were not viable with the earlier version. These include the faint-end of the ultra-violet luminosity function of galaxies (which can get affected by the radiative feedback) and the temperature-density relation of the low-density IGM at z ∼ 6. We study the effect of varying the free parameters and prescriptions of our model on a variety of observables. The conclusion of our analysis is that it should be possible to put constraints on the evolution of thermal and ionization state of the IGM using available observations accounting for all possible variations in the free parameters. A detailed exploration of the parameter space will be taken up in the future.
9 citations
TL;DR: In this paper , the authors developed an organometallic synthesis of nickel nitride nanoparticles supported on carbon (Ni3N-C) as the catalyst for both urea oxidation reaction (UOR) and hydrogen evolution reaction (HER).
Abstract: The sluggish kinetics of the anodic oxygen evolution reaction (OER) limit the overall efficiency of green hydrogen production. The proposed strategy to overcome this is to replace OER with other kinetically favorable anodic reactions like urea oxidation reaction (UOR). Herein, we develop an organometallic synthesis of nickel nitride nanoparticles supported on carbon (Ni3N–C) as the catalyst for both UOR and hydrogen evolution reaction (HER). A precious group metal-free electrolyzer based on Ni3N–C catalyst (as both anode and cathode) is implemented for the first time, and the urea electrolyzer cell has a 200 mV lower overpotential compared to that of the water electrolyzer.
8 citations
TL;DR: In this article , a pairwise connected tensor network path integral (PCTNPI) is proposed for real-time path integrals involving the Feynman-Vernon influence functional.
Abstract: It has been recently shown how the tensorial nature of real-time path integrals involving the Feynman-Vernon influence functional can be utilized using matrix product states, taking advantage of the finite length of the non-Markovian memory. Tensor networks promise to provide a new, unified language to express the structure of path integral. Here, a generalized tensor network is derived and implemented specifically incorporating the pairwise interaction structure of the influence functional, allowing for a compact representation and efficient evaluation. This pairwise connected tensor network path integral (PCTNPI) is illustrated through applications to typical spin-boson problems and explorations of the differences caused by the exact form of the spectral density. The storage requirements and performance are compared with iterative quasi-adiabatic propagator path integral and iterative blip-summed path integral. Finally, the viability of using PCTNPI for simulating multistate problems is demonstrated taking advantage of the compressed representation.
7 citations
TL;DR: In this paper , a mesoporous SiO2 nanomatrix using rice husks as a precursor through a facile thermal combustion process was synthesized using Rice husks.
Abstract: We synthesized mesoporous SiO2 nanomatrix using rice husks as a precursor through a facile thermal combustion process. XRD, FTIR, EDX, and TEM analyses were used to validate the produced mesoporous SiO2 nanomatrix. Electrochemical measurements were used to determine the specific capacitance of mesoporous SiO2 nanomatrix, and the results showed that the specific capacitances are 216, 204, 182, 163, 152, 142, 135, 133, 124.4, 124 F/g at current densities of 0.5, 1, 2, 4, 6, 8, 10, 12, 14, and 16 A/g. The benefit of impurities, as well as the large surface area and mesoporous structure of rice husk derived SiO2 nanostructures, allow Faradaic redox reactions at the electrode surface and the resulting supercapacitive behavior. This research might lead to a low-cost technique of producing supercapacitor electrodes using rice husk-derived SiO2 as a precursor.
7 citations
TL;DR: In the cell, the protein domains are attached with the short oligopeptide, commonly known as linker peptide as mentioned in this paper, which assists in domain-domain interaction and protein folding into the peculiar conformations.
TL;DR: In this paper , the authors discuss the double trumpet path integral and argue that with suitable twisted boundary conditions, a divergence in the moduli space integral can be avoided and the system can tunnel from a contracting phase to an expanding one avoiding a potential big bang/big crunch singularity.
Abstract: A bstract We discuss JT gravity in AdS and dS space in the second order formalism. For the pure dS JT theory without matter, we show that the path integral gives rise in general to the Hartle-Hawking wave function which describes an arbitrary number of disconnected universes produced by tunnelling “from nothing”, or to transition amplitudes which describe the tunnelling of an initial state consisting of several contracting universes to a final state of several expanding universes. These processes can be described by a hologram consisting of Random Matrix Theory (RMT) or, we suggest, after some modification on the gravity side, by a hologram with the RMT being replaced by SYK theory. In the presence of matter, we discuss the double trumpet path integral and argue that with suitable twisted boundary conditions, a divergence in the moduli space integral can be avoided and the system can tunnel from a contracting phase to an expanding one avoiding a potential big bang/big crunch singularity. The resulting spectrum of quantum perturbations which are produced can exhibit interesting departures from scale invariance. We also show that the divergence in moduli space can be avoided for suitable correlators which involve different boundaries in the AdS/dS cases, and suggest that a hologram consisting of the SYK theory with additional matter could get rid of these divergences in general. Finally, we analyse the AdS double trumpet geometry and show that going to the micro-canonical ensemble instead of the canonical one, for the spectral form factor, does not get rid of the divergence in moduli space.
TL;DR: In this article , an upper limit on the mass of a black hole set by the pair-instability supernovae (PISN) process can be useful in inferring the redshift of the GW sources by lifting the degeneracy between mass and redshift.
Abstract: ABSTRACT An upper limit on the mass of a black hole set by the pair-instability supernovae (PISN) process can be useful in inferring the redshift of the gravitational wave (GW) sources by lifting the degeneracy between mass and redshift. However, for this technique to work, it is essential that the PISN mass scale is redshift independent or at least has a predictable redshift dependence. We show that the observed PISN mass scale can get smeared and the position of the PISN mass scale is likely to exhibit a strong redshift dependence due to a combined effect from the non-zero value of the delay time between the formation of a star and the merging of two black holes and the metallicity dependence of PISN mass scale. Due to the unknown form of the delay-time distribution, the redshift dependence of the PISN mass cutoff of the binary black holes (BBHs) cannot be well characterized and will exhibit a large variation with the change in redshift. As a result, the use of a fixed PISN mass scale to infer the redshift of the BBHs from the observed masses will be systematically biased. Though this uncertainty is not severe for the third observation run conducted by the LIGO–Virgo–KAGRA collaboration, in the future this uncertainty will cause a systematic error in the redshift inferred from the PISN mass scale. The corresponding systematic error will be a bottleneck in achieving a few per cent precision measurements of the cosmological parameters using this method in the future.
TL;DR: In this paper , an extended version of the explicitly photon-conserving seminumerical model of reionization, script, which also includes thermal evolution of the intergalactic medium (IGM), was used to constrain these free parameters by simultaneously matching with various observational probes.
Abstract: ABSTRACT Given that the reionization history of cosmic hydrogen is yet to be stringently constrained, it is worth checking the prospects of doing so using physically motivated models and available observational data. For this purpose, we use an extended version of the explicitly photon-conserving seminumerical model of reionization, script, which also includes thermal evolution of the intergalactic medium (IGM). The model incorporates the effects of inhomogeneous recombination and radiative feedback self-consistently and is characterized by five free parameters (two for the redshift-dependent ionization efficiency, two for the ionizing escape fraction, and another for reionization temperature increment). We constrain these free parameters by simultaneously matching with various observational probes, e.g. estimates of the ionized hydrogen fraction, the CMB scattering optical depth and the galaxy UV luminosity function. In addition, we include the low-density IGM temperature measurements obtained from Lyman-α absorption spectra at z∼5.5, a probe not commonly used for Bayesian analysis of reionization parameters. We find that the interplay of the various data sets, particularly inclusion of the temperature data, leads to tightening of the parameter constraints. Our default models prefer a late end of reionization (at z ≲ 6), in agreement with other recent studies. We can also derive constraints on the duration of reionization, $\Delta z=1.81^{+0.51}_{-0.67}$ and the mid-point of reionization, $z_{\mathrm{mid}}=7.0^{+0.30}_{-0.40}$. The constraints can be further tightened by including other available and upcoming data sets.
TL;DR: In this paper , the authors present a summary of recent efforts in the design and optimization of metal-based small-molecule 'theranostic' anticancer agents and highlight the advantages of a theranostic candidate over the purely therapeutic or diagnostic agent in terms of evaluation of its biological properties.
Abstract: Around 10 million fatalities were recorded worldwide in 2020 due to cancer and statistical projections estimate the number to increase by 60% in 2040. With such a substantial rise in the global cancer burden, the disease will continue to impose a huge socio-economic burden on society. Currently, the most widely used clinical treatment modality is cytotoxic chemotherapy using platinum drugs which is used to treat variety of cancers. Despite its clinical success, critical challenges like resistance, off-target side effects and cancer variability often reduce its overall therapeutic efficiency. These challenges require faster diagnosis, simultaneous therapy and a more personalized approach toward cancer management. To this end, small-molecule 'theranostic' agents have presented a viable solution combining diagnosis and therapy into a single platform. In this review, we present a summary of recent efforts in the design and optimization of metal-based small-molecule 'theranostic' anticancer agents. Importantly, we highlight the advantages of a theranostic candidate over the purely therapeutic or diagnostic agent in terms of evaluation of its biological properties.
TL;DR: In this article , the authors give a pedagogical introduction to the superconformal index and present a series of lectures geared towards a beginning graduate student interested in working with the superconsistent index.
Abstract: Abstract In these lectures, we give a pedagogical introduction to the superconformal index. This is the writeup of the lectures given at the Winter School ‘YRISW 2020’ and is to appear in a special issue of J. Phys. A. The lectures are at a basic level and are geared towards a beginning graduate student interested in working with the superconformal index.
TL;DR: In this article, it was shown that for a regular local ring R containing an infinite field, the natural map S L r (R [ X ], ( X 2 − X ) / E r ( R [ X, X 2, X ) ) → S K 1 (R[ X ], (X 2 − x ) ) is an isomorphism for r ≥ 3.
TL;DR: In this paper , the authors analyzed the constraints imposed by unitarity and crossing symmetry on conformal theories in large dimensions and showed that the four-point function of identical scalar operators ϕ with scaling dimension ∆ ϕ such that ϕ /D < 3 / 4, is necessarily that of the generalized free field theory.
Abstract: A bstract In this paper, we analyze the constraints imposed by unitarity and crossing symmetry on conformal theories in large dimensions. In particular, we show that in a unitary conformal theory in large dimension D , the four-point function of identical scalar operators ϕ with scaling dimension ∆ ϕ such that ∆ ϕ /D < 3 / 4, is necessarily that of the generalized free field theory. This result follows only from crossing symmetry and unitarity. In particular, we do not impose the existence of a conserved spin two operator (stress tensor). We also present an argument to extend the applicability of this result to a larger range of conformal dimensions, namely to ∆ ϕ /D < 1. This extension requires some reasonable assumptions about the spectrum of light operators. Together, these results suggest that if there is a non-trivial conformal theory in large dimensions, not necessarily having a stress tensor, then its relevant operators must be exponentially weakly coupled with the rest.
TL;DR: In this article , the authors used elastic scattering from a monocrystalline silver nanowire for the simultaneous detection of spin angular momentum (SAM) and orbital angular momentum of light beam.
Abstract: In recent times the spin angular momentum (SAM) and orbital angular momentum (OAM) of light have gained prominence because of their significance in optical communication systems, micromanipulation, and sub-wavelength position sensing. To this end, simultaneous detection of SAM and OAM of light beam is one of the important topics of research from both application and fundamental spin-orbit interaction (SOI) point of view. While interferometry and metasurface based approaches have been able to detect the states, the presented approach involves elastic scattering from a monocrystalline silver nanowire for the simultaneous detection of SAM and OAM state of a circularly polarized Laguerre–Gaussian beam. By employing Fourier plane (FP) microscopy, the transmitted scattered light intensity distribution in the FP is analyzed to reconstruct the SAM and OAM state unambiguously. The SAM and OAM induced transverse energy flow as well as the polarization dependent scattering characteristics of the nanowire is investigated to understand the detection mechanism. This method is devoid of complex nanofabrication techniques and to the authors' knowledge, is a first example of single nano-object based simultaneous SAM and OAM detection. The study will further the understanding of SOI effects and can be useful for on-chip optical detection and manipulation.
TL;DR: In this article , a comparison of the one-way geomechanically coupled and non-coupled models is presented, and the results suggest that computed fluid pressure response and CO2 distribution in the reservoir are significantly influenced by reservoir geOMEchanical properties.
TL;DR: In this paper, the existence of the HK density function for a graded pair (R, I ) is proved for the case where R is an N -graded domain of finite type over a perfect field and I ⊂ R is a graded ideal of finite colength.
05 Jul 2022
TL;DR: In this article , a data-driven, multi-messenger technique was proposed to address this question by exploiting the inevitable correlation between gravitational waves and atomic/molecular emission-line signals.
Abstract: Abstract The formation of compact objects—neutron stars, black holes, and supermassive black holes—and their connection to the chemical composition of galaxies is one of the central questions in astrophysics. We propose a novel data-driven, multi-messenger technique to address this question by exploiting the inevitable correlation between gravitational waves and atomic/molecular emission-line signals. For a fiducial probability distribution function p ( t d ) ∝ t d − κ of time delays, this method can provide a measurement of the minimum delay time of 0.5 Gyr and a power-law index of κ = 1 with a standard deviation of 0.12 (and 0.45) and 0.06 (and 0.34), respectively, from five years of LIGO–Virgo–KAGRA observations in synergy with SPHEREx line intensity mapping (and DESI emission-line galaxies). Such measurements will provide data-driven, multi-messenger constraints on the delay time distribution which is currently not well known.
TL;DR: In this paper, the authors studied the well-posedness of a system of one-dimensional partial differential equations modeling blood flows in a network of vessels with viscoelastic walls and proved the existence and uniqueness of maximal strong solution for this type of hyperbolic/parabolic model.
Abstract: We study the well-posedness of a system of one-dimensional partial differential equations modeling blood flows in a network of vessels with viscoelastic walls. We prove the existence and uniqueness of maximal strong solution for this type of hyperbolic/parabolic model. We also prove a stability estimate under suitable nonlinear Robin boundary conditions.
TL;DR: In this article , the authors identify and compute such appropriate Hilbert-space correlations which carry information of entanglement for many-body localized (MBL) eigenstates and show that these correlations are qualitatively different not only from those of ergodic states but also of sparse random states with fractal statistics.
Abstract: Eigenstates of many-body localized (MBL) systems are characterized by area-law bipartite entanglement along with multifractal statistics of their amplitudes on Hilbert space. At the same time, sparse random pure states with fractal statistics are not compatible with area law and necessarily exhibit volume-law entanglement. This raises the question regarding what correlation functions of Hilbert-space amplitudes MBL eigenstates must possess for their area-law entanglement to be compatible with their multifractality. In this Letter, we identify and compute such appropriate Hilbert-space correlations which carry information of entanglement. We find that, for MBL eigenstates, these correlations are qualitatively different not only from those of ergodic states but also of sparse random states with fractal statistics. This enables us to show that indeed the said correlations lie at the heart of the coexistence of area-law entanglement and multifractality for MBL eigenstates.
TL;DR: In this article , a conformally covariant momentum space representation of CFT correlation functions is proposed, which reduces to the S-matrix in the flat space limit by keeping all the particle masses fixed as the conformal dimensions go to infinity along with the AdS radius.
Abstract: A bstract In this paper, we propose a conformally covariant momentum space representation of CFT correlation functions. We call it the AdS S-matrix. This representation has the property that it reduces to the S-matrix in the flat space limit. The flat space limit in question is taken by keeping all the particle masses fixed as the operator conformal dimensions go to infinity along with the AdS radius R. We give Feynman-like rules to compute the AdS S-matrix in 1 / R perturbation theory. Moreover, we relate it to the Mellin space representation of the conformal correlators in 1 / R perturbation theory.
TL;DR: In this article, the authors compared Maltose Binding Protein (MBP) with NT* for enhancing the solubility of the passenger protein. And they found that although the overall expression levels for NT* fusions are much higher than those for the MBP fusion, MBP was far superior for improving the passenger proteins' performance.
TL;DR: In this paper , the authors show that the Belle II experiment is the perfect laboratory for the search of particles that couple weakly to the Standard Model and have a characteristic decay length of a few centimetres and more.
Abstract: A bstract With a design luminosity of 50 ab − 1 and detectors with tracking capabilities extending beyond 1 m, the Belle II experiment is the perfect laboratory for the search of particles that couple weakly to the Standard Model and have a characteristic decay length of a few centimetres and more. We show that for models of dark photons and other light vector bosons, Belle II will be successful in probing regions of parameter space which are as of now unexplored by any experiment. In addition, for models where the vector boson couples sub-dominantly to the electron and quarks as compared to muons, e.g. in the L μ −L τ model, Belle II will probe regions of mass and couplings compatible with the anomalous magnetic moment of muon. We discuss these results and derive the projected sensitivity of Belle II for a handful of other models. Finally, even with the currently accumulated data, ∼ 200 fb − 1 , Belle II should be able to cover regions of parameter space pertaining to the X(17) boson postulated to solve the ATOMKI anomaly.
TL;DR: In this article, a first-order Godunov-type scheme for weakly hyperbolic pressureless gas dynamics equations and augmented Burgers' equations was proposed and tested on a number of numerical examples for one and two-dimensional pressureless equations.