Tata Institute of Fundamental Research

About: Tata Institute of Fundamental Research is a education organization based out in Mumbai, Maharashtra, India. It is known for research contribution in the topics: Magnetization & Large Hadron Collider. The organization has 7786 authors who have published 21742 publications receiving 622368 citations. The organization is also known as: TIFR.

Stability constraints on classical de Sitter vacua

Abstract: We present further no-go theorems for classical de Sitter vacua in Type II string theory, i.e., de Sitter constructions that do not invoke non-perturbative effects or explicit supersymmetry breaking localized sources. By analyzing the stability of the 4D potential arising from compactification on manfiolds with curvature, fluxes, and orientifold planes, we found that additional ingredients, beyond the minimal ones presented so far, are necessary to avoid the presence of unstable modes. We enumerate the minimal setups for (meta)stable de Sitter vacua to arise in this context.

Near UV-Visible electronic absorption originating from charged amino acids in a monomeric protein

Abstract: Electronic absorption spectra of proteins are primarily characterized over the ultraviolet region (185–320 nm) of the electromagnetic spectrum. While recent studies on peptide aggregates have revealed absorption beyond 350 nm, monomeric proteins lacking aromatic amino acids, disulphide bonds, and active site prosthetic groups are expected to remain optically silent beyond 250 nm. Here, in a joint theoretical and experimental investigation, we report the distinctive UV-Vis absorption spectrum between 250 nm [e = 7338 M−1 cm−1] and 800 nm [e = 501 M−1 cm−1] in a synthetic 67 residue protein (α3C), in monomeric form, devoid of aromatic amino acids. Systematic control studies with high concentration non-aromatic amino acid solutions revealed significant absorption beyond 250 nm for charged amino acids which constitute over 50% of the sequence composition in α3C. Classical atomistic molecular dynamics (MD) simulations of α3C reveal dynamic interactions between multiple charged sidechains of Lys and Glu residues present in α3C. Time-dependent density functional theory calculations on charged amino acid residues sampled from the MD trajectories of α3C reveal that the distinctive absorption features of α3C may arise from two different types of charge transfer (CT) transitions involving spatially proximal Lys/Glu amino acids. Specifically, we show that the charged amino (NH3+)/carboxylate (COO−) groups of Lys/Glu sidechains act as electronic charge acceptors/donors for photoinduced electron transfer either from/to the polypeptide backbone or to each other. Further, the sensitivity of the CT spectra to close/far/intermediate range of encounters between sidechains of Lys/Glu owing to the three dimensional protein fold can create the long tail in the α3C absorption profile between 300 and 800 nm. Finally, we experimentally demonstrate the sensitivity of α3C absorption spectrum to temperature and pH-induced changes in protein structure. Taken together, our investigation significantly expands the pool of spectroscopically active biomolecular chromophores and adds an optical 250–800 nm spectral window, which we term ProCharTS (Protein Charge Transfer Spectra), for label free probes of biomolecular structure and dynamics.

Study of doubly heavy tetraquarks in Lattice QCD

Abstract: We present the results of a lattice calculation of tetraquark states with quark contents ${q}_{1}{q}_{2}\overline{Q}\overline{Q},{q}_{1},{q}_{2}\ensuremath{\subset}u,d,s,c$ and $Q\ensuremath{\equiv}b$, $c$ in both spin-0 ($J=0$) and spin-1 ($J=1$) sectors. This calculation is performed on three dynamical ${N}_{f}=2+1+1$ highly improved staggered quark ensembles at lattice spacings of about 0.12, 0.09, and 0.06 fm. We use the overlap action for light to charm quarks, while a nonrelativistic action with nonperturbatively improved coefficients with terms up to $\mathcal{O}({\ensuremath{\alpha}}_{s}{v}^{4})$ is employed for the bottom quark. While considering charm or bottom quarks as heavy, we calculate the energy levels of various four-quark configurations with light quark masses ranging from the physical strange quark mass to that of the corresponding physical pion mass. This enables us to explore the quark mass dependence of the extracted four-quark energy levels over a wide range of quark masses. The results of the spin-1 states show the presence of ground state energy levels which are below their respective thresholds for all the light flavor combinations. Further, we identify a trend that the energy splittings, defined as the energy difference between the ground state energy levels and their respective thresholds, increase with decreasing the light quark masses and are maximum at the physical point for all the spin-1 states. The rate of increase is, however, dependent on the light quark configuration of the particular spin-1 state. We also present a study of hadron mass relations involving tetraquarks, baryons, and mesons arising in the limit of infinitely heavy quarks and find that these relations are more compatible with the heavy quark limit in the bottom sector but deviate substantially in the charm sector. The ground state spectra of the spin-0 tetraquark states with various flavor combinations are seen to lie above their respective thresholds.

Evidence for particle re-acceleration in the radio relic in the galaxy cluster PLCKG287.0+32.9

Abstract: Radio relics are diffuse radio sources observed in galaxy clusters, probably produced by shock acceleration during cluster-cluster mergers. Their large size, of the order of 1 Mpc, indicates that the emitting electrons need to be (re)accelerated locally. The usually invoked diffusive shock acceleration models have been challenged by recent observations and theory. We report the discovery of complex radio emission in the Galaxy cluster PLCKG287.0+32.9, which hosts two relics, a radio halo, and several radio filamentary emission. Optical observations suggest that the cluster is elongated, likely along an intergalactic filament, and displays a significant amount of substructure. The peculiar features of this radio relic are that (1) it appears to be connected to the lobes of a radio galaxy and (2) the radio spectrum steepens on either side of the radio relic. We discuss the origins of these features in the context of particle re-acceleration.

Evidence for direct CP violation in the decay B±→ D(*)K±, D→KS0π+π - and measurement of the CKM phase φ3

Abstract: We present a new measurement of the unitarity triangle angle phi(3) using a Dalitz plot analysis of the K-S(0)pi(+)pi(-) decay of the neutral D meson produced in B-+/- -> D-(*()) K-+/- decays. The method exploits the interference between D-0 and (D) over bar (0) to extract the angle phi(3), strong phase delta, and the ratio r of suppressed and allowed amplitudes. We apply this method to a 605 fb(-1) data sample collected by the Belle experiment. The analysis uses three decays: B-+/- -> DK +/-, and B-+/- -> D*K-+/- with D* -> D pi(0) and D* -> D gamma, as well as the corresponding charge-conjugate modes. From a combined maximum likelihood fit to the three modes, we obtain phi(3) = 78.4 degrees (+10.8 degrees)(-11.6 degrees) +/- 3.6 degrees (syst) +/- 8.9 degrees (model). CP conservation in this process is ruled out at the confidence level (1 - CL) = 5 X 10(-4), or 3.5 standard deviations.