Density of defects and the scaling law of the entanglement entropy in quantum phase transition of one dimensional spin systems induced by a quench

We have studied quantum phase transition induced by a quench in different one dimensional spin systems. Our analysis is based on the dynamical mechanism which envisages nonadiabaticity in the vicinity of the critical point. This causes spin fluctuation which leads to the random fluctuation of the Berry phase factor acquired by a spin state when the ground state of the system evolves in a closed path. The two-point correlation of this phase factor is associated with the probability of the formation of defects. In this framework, we have estimated the density of defects produced in several one dimensional spin chains. At the critical region, the entanglement entropy of a block of $L$ spins with the rest of the system is also estimated which is found to increase logarithmically with $L$. The dependence on the quench time puts a constraint on the block size $L$. It is also pointed out that the Lipkin-Meshkov-Glick model in point-splitting regularized form appears as a combination of the XXX model and Ising model with magnetic field in the negative z-axis. This unveils the underlying conformal symmetry at criticality which is lost in the sharp point limit. Our analysis shows that the density of defects as well as the scaling behavior of the entanglement entropy follows a universal behavior in all these systems.Comment: 4 figures, Accepted in Phys. Rev.

An experimental study of the swelling properties of spherical hydro-gel immersed in water and the formulation of a simple theoretical model for its explanation

The mechanism of variation of mass and volume, through the absorption of water, by the most commonly used and abundantly available spherical hydro-gel beads of various colors has been studied. Immersing the beads in distilled water, both mass and volume were measured at regular intervals. By an analysis of mass-versus-time data, using standard theoretical methods, the mechanism of diffusion of water has been studied. Relaxation controlled transport was found to be the predominant process of diffusion of water into the materials under study. The diffusion coefficient has been determined for hydro-gels of different colors. Various swelling related parameters such as equilibrium water content, equilibrium swelling ratio, characteristic time, initial rate of water absorption etc. were determined for these hydro-gels. The maximum attainable mass and the maximum number of water molecules that can be attached to active polymer sites in a single bead have been calculated. In this regard, the number of such active sites per unit volume and mass of dry hydro-gel was determined. A theoretical model has been developed, based on the consideration of water absorption through the occupation of vacant polymer sites in a highly porous hydro-gel. Considerations of cylindrical and spherical pores in this model predicted almost the same swelling behavior. Expressions relating mass and volume with time have been formulated and they agreed well with experimental observations. The dependence of characteristic time () upon structural parameters have been established. Values of swelling related parameters have been determined by a numerical fitting of theoretical model to experimental data. The agreement of experimental findings with theoretical predictions has been depicted graphically

Quantum Cournot equilibrium for the Hotelling-Smithies model of product choice

This paper demonstrates the quantization of a spatial Cournot duopoly model with product choice, a two stage game focusing on non-cooperation in locations and quantities. With quantization, the players can access a continuous set of strategies, using continuous variable quantum mechanical approach. The presence of quantum entanglement in the initial state identifies a quantity equilibrium for every location pair choice with any transport cost. Also higher profit is obtained by the firms at Nash equilibrium. Adoption of quantum strategies rewards us by the existence of a larger quantum strategic space at equilibrium.Comment: 13 pages, 6 tables, 8 figure

An experimental study of the swelling properties of spherical hydro-gel immersed in water and the formulation of a simple theoretical model for its explanation

The mechanism of variation of mass and volume, through the absorption of water, by the most commonly used and abundantly available spherical hydro-gel beads of various colors has been studied. Immersing the beads in distilled water, both mass and volume were measured at regular intervals. By an analysis of mass-versus-time data, using standard theoretical methods, the mechanism of diffusion of water has been studied. Relaxation controlled transport was found to be the predominant process of diffusion of water into the materials under study. The diffusion coefficient has been determined for hydro-gels of different colors. Various swelling related parameters such as equilibrium water content, equilibrium swelling ratio, characteristic time, initial rate of water absorption etc. were determined for these hydro-gels. The maximum attainable mass and the maximum number of water molecules that can be attached to active polymer sites in a single bead have been calculated. In this regard, the number of such active sites per unit volume and mass of dry hydro-gel was determined. A theoretical model has been developed, based on the consideration of water absorption through the occupation of vacant polymer sites in a highly porous hydro-gel. Considerations of cylindrical and spherical pores in this model predicted almost the same swelling behavior. Expressions relating mass and volume with time have been formulated and they agreed well with experimental observations. The dependence of characteristic time () upon structural parameters have been established. Values of swelling related parameters have been determined by a numerical fitting of theoretical model to experimental data. The agreement of experimental findings with theoretical predictions has been depicted graphically

Detectable abundance of cyanoacetylene (hc3n) predicted on reduced nitrogen-rich super-earth atmospheres

Abstract: We predict that cyanoacetylene (HC3N) is produced photochemically in the atmosphere of GJ 1132 b in abundances detectable by the James Webb Space Telescope (JWST), assuming that the atmosphere is hydrogen dominated and rich in molecular nitrogen (N2), methane (CH4), and hydrogen cyanide (HCN), as described by Swain et al. First, we construct line lists and cross sections for HC3N. Then we apply these cross sections and the model atmosphere of Swain et al. to a radiative transfer model in order to simulate the transmission spectrum of GJ 1132 b as it would be seen by JWST, accounting for the uncertainty in the retrieved abundances. We predict that cyanoacetylene features at various wavelengths, with a clear lone feature at 4.5 μm, observable by JWST after one transit. This feature persists within the 1σ uncertainty of the retrieved abundances of HCN and CH4. The signal is detectable for stratospheric temperatures ≲600 K and moderate stratospheric mixing (106 cm2 s−1 ≲ K zz ≲ 108 cm2 s−1). Our results also indicate that HC3N is an important source of opacity that future retrieval models should consider

Follow-up observations of GW170817 with the MAGIC telescopes

The discovery of the electromagnetic counterpart AT2017gfo and the GRB 170817A, associated to the binary neutron star merger GW170817, was one of the major advances in the study of gamma-ray bursts (GRBs) and the hallmark of the multi-messenger astronomy with gravitational waves. Another breakthrough in GRB physics is represented by the discovery of the highly energetic, teraelectronvolt (TeV) component in the GRB 190114C, possibly an universal component in all GRBs. This conclusion is also suggested by the hint of TeV emission in the short GRB 160821B and a few more events reported in the literature. The missing observational piece is the joint detection of TeV emission and gravitational waves from a short GRB and its progenitor. MAGIC observed the counterpart AT2017gfo as soon as the visibility conditions allowed it, namely from January to June 2018. These observations correspond to the maximum flux level observed in the radio and X-ray bands. The upper limits derived from TeV observations are compared with the modelling of the late non-thermal emission using the multi-frequency SED

First detection of VHE gamma-ray emission from TXS 1515-273, study of its X-ray variability and spectral energy distribution

We report here on the first multi-wavelength (MWL) campaign on the blazar TXS 1515-273, undertaken in 2019 and extending from radio to very-high-energy gamma rays (VHE). Up until now, this blazar had not been the subject of any detailed MWL observations. It has a rather hard photon index at GeV energies and was considered a candidate extreme high-synchrotronpeaked source. MAGIC observations resulted in the first-time detection of the source in VHE with a statistical significance of 7.6$\sigma$. The average integral VHE flux of the source is 6 $\pm$ 1% of the Crab nebula flux above 400 GeV. X-ray coverage was provided by Swift-XRT, XMMNewton, and NuSTAR. The long continuous X-ray observations were separated by $\sim$ 9 h, both showing clear hour scale flares. In the XMM-Newton data, both the rise and decay timescales are longer in the soft X-ray than in the hard X-ray band, indicating the presence of a particle cooling regime. The X-ray variability timescales were used to constrain the size of the emission region and the strength of the magnetic field. The data allowed us to determine the synchrotron peak frequency and classify the source as a flaring high, but not extreme, synchrotron peaked object. Considering the constraints and variability patterns from the X-ray data, we model the broad-band spectral energy distribution. We applied a simple one-zone model, which could not reproduce the radio emission and the shape of the optical emission, and a two-component leptonic model with two interacting components, enabling us to reproduce the emission from radio to VHE band

MAGIC observations of the nearby short GRB 160821B

Gamma-ray bursts (GRBs), the most luminous explosions in the universe, have at least two types known. One of them, short GRBs, have been thought to originate from binary neutron star (BNS) mergers. The discovery of GW170817 together with a GRB was the first and only direct proof of the hypothesis, and thus the properties of the short GRBs are poorly known yet. Aiming to clarify the underlying physical mechanisms of the short GRBs, we analyzed GRB 160821B, one of the nearest short GRBs known at z=0.162, observed with the MAGIC telescopes. A hint of a gamma-ray signal is found above 0.5 TeV at a significance of >3 sigma during observations from 24 seconds until 4 hours after the burst, as presented in the past. Recently, multi-wavelength data of its afterglow emission revealed a well-sampled kilonova component from a BNS merger, and the importance of GRB 160821B increased concerning GRB-GW studies. Accordingly, we investigated GRB afterglow models again, using the revised multi-wavelength data. We found that the straightforward interpretation with one-zone synchrotron self-Compton model from the external forward shock is in tension with the observed TeV flux, contradicting the suggestion reported previously. In this contribution we discuss the implication from the TeV observation, including alternative scenarios where the TeV emission can be enhanced. We also give a brief outlook of future GeV-TeV observations of short GRBs with imaging atmospheric Cherenkov telescopes, which could shed more light on the GRB-BNS merger relation

A lower bound on intergalactic magnetic fields from time variability of 1ES 0229+200 from MAGIC and Fermi/LAT observations

Extended and delayed emission around distant TeV sources induced by the effects of propagation of gamma rays through the intergalactic medium can be used for the measurement of the intergalactic magnetic field (IGMF). We search for delayed GeV emission from the hard-spectrum TeV blazar 1ES 0229+200 with the goal to detect or constrain the IGMF-dependent secondary flux generated during the propagation of TeV gamma rays through the intergalactic medium. We analyze the most recent MAGIC observations over a 5 year time span and complement them with historic data of the H.E.S.S. and VERITAS telescopes along with a 12-year long exposure of the Fermi/LAT telescope. We use them to trace source evolution in the GeV-TeV band over one-and-a-half decade in time. We use Monte Carlo simulations to predict the delayed secondary gamma-ray flux, modulated by the source variability, as revealed by TeV-band observations. We then compare these predictions for various assumed IGMF strengths to all available measurements of the gamma-ray flux evolution. We find that the source flux in the energy range above 200 GeV experiences variations around its average on the 14 years time span of observations. No evidence for the flux variability is found in 1-100 GeV energy range accessible to Fermi/LAT. Non-detection of variability due to delayed emission from electromagnetic cascade developing in the intergalactic medium imposes a lower bound of B>1.8e-17 G for long correlation length IGMF and B>1e-14 G for an IGMF of the cosmological origin. Though weaker than the one previously derived from the analysis of Fermi/LAT data, this bound is more robust, being based on a conservative intrinsic source spectrum estimate and accounting for the details of source variability in the TeV energy band. We discuss implications of this bound for cosmological magnetic fields which might explain the baryon asymmetry of the Universe.Comment: 10 pages, 5 figures, accepted to A&A. Corresponding authors: Ievgen Vovk, Paolo Da Vela (mailto:[email protected]) and Andrii Neronov (mailto:[email protected]

Multiwavelength monitoring of the gravitationally lensed blazar QSO B0218+357 between 2016 and 2020

QSO B0218+357 is currently the only gravitationally lensed source from which very-high-energy (VHE, &100GeV) gamma-ray emission has been detected. We report the multiwavelength monitoring observations of this source performed between 2016 and 2020 in radio interferometry, optical, X-ray and gamma-ray bands. During the monitoring individual flares and hints of enhanced states in optical, X-ray and GeV bands have been observed, and the simultaneous data taken by the MAGIC telescopes allow us to search for the VHE gamma-ray emission associated with these events