Physics
http://repository.iitgn.ac.in/handle/123456789/607
2017-06-27T03:35:55ZUpper limits on gravitational waves from scorpius X-1 from a model-based cross-correlation search in Advanced LIGO data
http://repository.iitgn.ac.in/handle/123456789/2994
Upper limits on gravitational waves from scorpius X-1 from a model-based cross-correlation search in Advanced LIGO data
Sengupta, Anand
2017-06-01T00:00:00ZRefractive index of an anisotropic Quark-Gluon-Plasma medium in an effective description of hot QCD
http://repository.iitgn.ac.in/handle/123456789/2993
Refractive index of an anisotropic Quark-Gluon-Plasma medium in an effective description of hot QCD
Jamal, M. Yousuf; Mitra, Sukanya; Chandra, Vinod
2017-06-01T00:00:00ZCollective excitations of hot QCD medium in a quasiparticle description
http://repository.iitgn.ac.in/handle/123456789/2982
Collective excitations of hot QCD medium in a quasiparticle description
Jamal, M. Yousuf; Mitra, Sukanya; Chandra, Vinod
Collective excitations of a hot QCD medium are the main focus of this article. The analysis is performed within semiclassical transport theory with isotropic and anisotropic momentum distribution functions for the gluonic and quark-antiquark degrees of freedom that constitutes the hot QCD plasma. The isotropic/equilibrium momentum distributions for gluons and quarks are based on a recent quasiparticle description of hot QCD equations of state. These effective momentum distribution functions for quasigluons and quasiquarks that encode hot QCD medium effects in terms of temperature dependent effective gluon and effective quark fugacities turned out to be isotropic in momentum. The anisotropic distributions are just the extensions of isotropic ones by stretching or squeezing them in one of the directions. The hot QCD medium effects in the model adopted here enter through the effective gluon and quark fugacities along with nontrivial dispersion relations leading to an effective QCD coupling constant. The semiclassical transport theory for computing the gluon polarization for the isotropic distributions (assuming a hot QCD medium as the ultrarelativistic system of gluons and quark/antiquarks) can straightforwardly be extended in the present case. The interactions mainly modify the Debye mass parameter and, in turn, the effective coupling in the medium. These modifications have been seen to modify the collective modes of the hot QCD plasma in a significant way.
2017-05-01T00:00:00ZGW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2
http://repository.iitgn.ac.in/handle/123456789/2968
GW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2
Sengupta, Anand
We describe the observation of GW170104, a gravitational-wave signal produced by the coalescence of a pair of stellar-mass black holes. The signal was measured on January 4, 2017 at 10∶11:58.6 UTC by the twin advanced detectors of the Laser Interferometer Gravitational-Wave Observatory during their second observing run, with a network signal-to-noise ratio of 13 and a false alarm rate less than 1 in 70 000 years. The inferred component black hole masses are
31.
2
+
8.4
−
6.0
M
⊙
and
19.
4
+
5.3
−
5.9
M
⊙
(at the 90% credible level). The black hole spins are best constrained through measurement of the effective inspiral spin parameter, a mass-weighted combination of the spin components perpendicular to the orbital plane,
χ
eff
=
−
0.1
2
+
0.21
−
0.30
. This result implies that spin configurations with both component spins positively aligned with the orbital angular momentum are disfavored. The source luminosity distance is
88
0
+
450
−
390
Mpc
corresponding to a redshift of
z
=
0.1
8
+
0.08
−
0.07
. We constrain the magnitude of modifications to the gravitational-wave dispersion relation and perform null tests of general relativity. Assuming that gravitons are dispersed in vacuum like massive particles, we bound the graviton mass to
m
g
≤
7.7
×
10
−
23
eV
/
c
2
. In all cases, we find that GW170104 is consistent with general relativity.
2017-06-01T00:00:00Z