Physicshttp://repository.iitgn.ac.in/handle/123456789/6072017-06-23T13:41:19Z2017-06-23T13:41:19ZCollective excitations of hot QCD medium in a quasiparticle descriptionJamal, M. YousufMitra, SukanyaChandra, Vinodhttp://repository.iitgn.ac.in/handle/123456789/29822017-06-23T12:21:10Z2017-05-01T00:00:00ZCollective 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 0.2Sengupta, Anandhttp://repository.iitgn.ac.in/handle/123456789/29682017-06-13T14:11:58Z2017-06-01T00:00:00ZGW170104: 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.
2017-06-01T00:00:00ZExothermicity is not a necessary condition for enhanced diffusion of enzymesIllien, PierreZhao, XiDey, Krishna K.Butler, Peter J.Sen, AyusmanGolestanian, Raminhttp://repository.iitgn.ac.in/handle/123456789/29662017-06-13T12:20:58Z2017-06-01T00:00:00ZExothermicity is not a necessary condition for enhanced diffusion of enzymes
Illien, Pierre; Zhao, Xi; Dey, Krishna K.; Butler, Peter J.; Sen, Ayusman; Golestanian, Ramin
Recent experiments have revealed that the diffusivity of exothermic and fast enzymes is enhanced when they are catalytically active, and different physical mechanisms have been explored and quantified to account for this observation. We perform measurements on the endothermic and relatively slow enzyme aldolase, which also shows substrate-induced enhanced diffusion. We propose a new physical paradigm, which reveals that the diffusion coefficient of a model enzyme hydrodynamically coupled to its environment increases significantly when undergoing changes in conformational fluctuations in a substrate concentration dependent manner, and is independent of the overall turnover rate of the underlying enzymatic reaction. Our results show that substrate-induced enhanced diffusion of enzyme molecules can be explained within an equilibrium picture, and that the exothermicity of the catalyzed reaction is not a necessary condition for the observation of this phenomenon.
2017-06-01T00:00:00ZOptical intra-day variability in 3C 66A: a decade of observationsKaur, NavpreetSameer, BaliyanKiran, S.Ganesh, S.http://repository.iitgn.ac.in/handle/123456789/29632017-06-05T12:37:08Z2017-05-01T00:00:00ZOptical intra-day variability in 3C 66A: a decade of observations
Kaur, Navpreet; Sameer, Baliyan; Kiran, S.; Ganesh, S.
We present results based on the observations of the blazar 3C 66A from 2005 November 06 to 2016 February 14 in the BVR and I broad-bands using the 1.2-m telescope of the Mt Abu InfraRed Observatory (MIRO). The source was observed on 160 nights; on 89 of these nights, it was monitored for more than 1 h to check for the presence of any intra-day variability (IDV). The blazar 3C 66A exhibited significant variations in the optical flux on short- and long-term time-scales. However, unlike the highly variable S5 0716+71, it showed an IDV duty cycle of about 8 per cent only. Our statistical studies suggest IDV time-scales ranging from ∼37 min to about 3.12 h and, in one case, the possibility of quasi-periodic variations with a characteristic time-scale of ∼1.4 h. The IDV amplitudes in the R band were found to vary from 0.03 mag to as much as 0.6 mag, with a larger amplitude of variation when the source was relatively fainter. The typical rate of the flux variation was estimated to be ∼0.07 mag h−1 in both the rising and the falling phases. However, rates of brightness variation as high as 1.38 mag h−1 were also detected. The shortest time-scale of the variation (i.e. 37 min) sets an upper limit of 6.92 × 1014 cm on the size of the emission region and about 3.7 × 108 M⊙ as an estimate of the mass of the black hole, assuming that the origin of the rapid optical variability is in close vicinity to the central supermassive black hole. The long-term study suggests a mild bluer-when-brighter behaviour, typical for BL Lacertae objects.
2017-05-01T00:00:00Z