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.

Size effect study in magnetoelectric BiFeO3 system

Abstract: In this paper, we report for the first time finite size effects on Neel temperature (T N) of magnetoelectric BiFeO3 system. Novel wet chemical route has been developed to produce fine particles of BiFeO3 with controlled size and size distribution. Unlike other oxide systems, lattice volume contraction has been observed with decrease in particle size. The decrease in T N is co-related to unit cell volume contraction occurring with reduction in particle size.

Improving the sensitivity of a search for coalescing binary black holes with nonprecessing spins in gravitational wave data

Abstract: We demonstrate for the first time a search pipeline with improved sensitivity to gravitational waves from coalescing binary black holes with spins aligned to the orbital angular momentum by the inclusion of spin effects in the search templates. We study the pipeline recovery of simulated gravitational wave signals from aligned-spin binary black holes added to real detector noise, comparing the pipeline performance with aligned-spin filter templates to the same pipeline with nonspinning filter templates. Our results exploit a three-parameter phenomenological waveform family that models the full inspiral-merger-ringdown coalescence and treats the effect of aligned spins with a single effective spin parameter χ. We construct template banks from these waveforms by a stochastic placement method and use these banks as filters in the recently developed gstlal search pipeline. We measure the observable volume of the analysis pipeline for binary black hole signals with M_(total) and χ∈[0,0.85]. We find an increase in observable volume of up to 45% for systems with 0.2≤χ≤0.85 with almost no loss of sensitivity to signals with 0≤χ≤0.2. We also show that the use of spinning templates in the search pipeline provides for more accurate recovery of the binary mass parameters as well as an estimate of the effective spin parameter. We demonstrate this analysis on 25.9 days of data obtained from the Hanford and Livingston detectors in LIGO’s fifth observation run.

Search for Subsolar-Mass Ultracompact Binaries in Advanced LIGO’s First Observing Run

Abstract: We present a search for subsolar mass ultracompact objects in data obtained during Advanced LIGO’s second observing run. In contrast to a previous search of Advanced LIGO data from the first observing run, this search includes the effects of component spin on the gravitational waveform. We identify no viable gravitational-wave candidates consistent with subsolar mass ultracompact binaries with at least one component between 0.2 M⊙–1.0 M⊙. We use the null result to constrain the binary merger rate of (0.2 M⊙, 0.2 M⊙) binaries to be less than 3.7×105 Gpc-3 yr-1 and the binary merger rate of (1.0 M⊙, 1.0 M⊙) binaries to be less than 5.2×103 Gpc-3 yr-1. Subsolar mass ultracompact objects are not expected to form via known stellar evolution channels, though it has been suggested that primordial density fluctuations or particle dark matter with cooling mechanisms and/or nuclear interactions could form black holes with subsolar masses. Assuming a particular primordial black hole (PBH) formation model, we constrain a population of merging 0.2 M⊙ black holes to account for less than 16% of the dark matter density and a population of merging 1.0 M⊙ black holes to account for less than 2% of the dark matter density. We discuss how constraints on the merger rate and dark matter fraction may be extended to arbitrary black hole population models that predict subsolar mass binaries.

Helioseismic measurement of the extent of overshoot below the solar convection zone

Abstract: The discontinuity in the derivatives of the sound speed at the base of the overshoot layer below the solar convection zone introduces a characteristic oscillatory component in the frequencies of solar p-modes as a function of the radial order n. The amplitude of this oscillatory part is calibrated as a function of the extent of overshoot using a sequence of solar models constructed with varying extent of overshoot. Using this calibration, an attempt is made to measure the extent of overshoot below the solar convection zone using the available frequencies of the p-modes. It is found that the observed frequencies are consistent with a solar model without overshoot. Further, taking account of the errors in observations, it is possible to put a 2-σ upper limit of 0.1 H p on the extent of overshoot.