Seminars

"Since Bell's theorem we know that quantum mechanics is incompatible with local hidden variable models, the phenomenon known as quantum nonlocality. However, in spite of steady progress over years, the precise characterization of the set of quantum correlations has remained an elusive quest. There are correlations compatible with the no-signaling principle and still beyond what can be achieved within quantum theory, what has motivated the search for physical principles and computational methods to decide the quantum or post-quantum behavior of correlations. Here we identify a yet new feature of Bell correlations that we call quantum voids: faces of the no-signaling set where all nonlocal correlations are postquantum. Considering the simplest possible Bell scenario we give a full characterization of quantum voids, also understanding its connections to known principles and its potential use as a dimension witness. Reference: A. Rai, C. Duarte, S. Brito, R. Chaves, Into the Quantum Void: Geometry of the Quantum Set on no Signaling Faces, quant-phys: arXiv:1812.06057 (Dec. 2018) [ Link: https://arxiv.org/abs/1812.06057 ]."

"We add new particles to the Standard Model at TeV scale, e.g., a gauge singlet scalar. Such new physics also provides a viable dark matter candidate. We have shown various phase diagrams and point out the regions of absolute stability, meta-stability and instability for the electroweak vacuum. We graphically demonstrate how the confidence level, at which stability of electroweak vacuum is excluded, depends on such new physics parameters."

"The intriguing question, why the present scale of the universe is free from any perceptible footprints of rank-2 antisymmetric tensor fields (generally known as Kalb-Ramond fields) is addressed. A quite natural explanation of this issue is given from the angle of higher-curvature gravity, both in four- and in five-dimensional spacetime. The results here obtained reveal that the amplitude of the Kalb-Ramond field may be actually large and play a significant role during the early universe, while the presence of higher-order gravity suppresses this field during the cosmological evolution, so that it eventually becomes negligible in the current universe. Besides the suppression of the Kalb-Ramond field, the extra degree of freedom in F(R) gravity, usually known as scalaron, also turns out to be responsible for inflation. Such F(R) gravity with Kalb-Ramond fields may govern the early universe to undergo an inflationary stage at early times (with the subsequent graceful exit) for wider range of F(R) gravity than without antisymmetric fields. Furthermore, the models—in four and five dimensional spacetimes are linked to observational constraints, with the conclusion that the corresponding values of the spectral index and tensor-to-scalar ratio closely match the values provided by the Planck survey 2018 data."

"ery strong magnetic fields can arise in non-central heavy-ion collisions at ultra-relativistic energies, which may not decay quickly in a conducting plasma. We carry out relativistic magneto-hydrodynamics (RMHD) simulations to study the effects of this magnetic field on the evolution of the fluid and on resulting flow fluctuations in the ideal RMHD limit. Our results show that the magnetic field leads to enhancement in elliptic flow for small impact parameters while it suppresses it for large impact parameters. Interestingly, we find that magnetic field in localized regions can temporarily increase in time as evolving fluid energy density fluctuations lead to reorganization of magnetic flux. This can have important effects on the chiral magnetic effect. We discuss the situation of nontrivial magnetic field configurations arising from collision of deformed nuclei and show that it can lead to anomalous elliptic flow. Special (crossed body-body) configurations of deformed nuclei collisions can lead to the presence of a quadrupolar magnetic field, which can have very important effects on the rapidity dependence of transverse expansion (similar to beam focusing from quadrupole fields in accelerators)."

"We will discuss various aspects of the Ramanujan-Petersson conjecture about the growth of the Fourier coefficients of cusp forms of half-integral weight. This is recent joint work with S. Gun"

"Blazars are active galactic nuclei with strong jets. They tend to exhibit dramatic and unpredictable flux variations, namely outbursts. Certain observed outbursts from an exceptional Blazar OJ287 can be explained by invoking a massive black hole binary as its central engine. Detailed General Relativistic modeling allowed us to predict a major optical outburst during November 2015. The outburst did occur within the expected time range, peaking on 5/12/2015. A multi-wavelength observational campaign confirmed the occurrence of certain impact flare and the presence of a major thermal component in the flare, as predicted. These observations and subsequent analysis allowed us to establish the presence of a spinning supermassive black hole binary that spirals in due to the emission of nano-Hertz gravitational waves in the central engine of OJ287. I will briefly list our on-going efforts that should be interesting to the Event Horizon Telescope consortium and the International Pulsar Timing Array."

"Pulsar timing array experiments aim to detect nanohertz gravitational waves (GWs) by precise timing of an ensemble of millisecond pulsars. Times of arrival (TOAs) of pulsar pulses are modulated in the presence of a GW, by an amount proportional to the antiderivative of the GW amplitude. In this talk, I present our latest results on efficient computation of GW-induced pulsar timing residuals due to eccentric supermassive black hole binaries. GW-induced timing residuals due to low-eccentricity binaries can be very efficiently computed using analytic post-circular waveforms developed by Boetzel et al. 2017 incorporating advance of periastron in a post-Newtonian (PN) accurate manner. I also introduce a novel semi-analytic solution to quadrupolar order orbital evolution equations which enables efficient computation of the Pulsar term in the timing residuals. This efficient solution also enables the computation of numerical arbitrary-eccentricity timing residuals incorporating exactly the reactive orbital evolution and advance of periastron. These results will be used to search for eccentric supermassive binaries in the International Pulsar Timing Array data."

"Fracmeet 2019"

"Fracmeet 2019"