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Sibaji Raha

Publications and source records attributed to Sibaji Raha.

At least 37 records · Page 2Linked to original sources
arXiv2012

Solving relativistic hydrodynamic equation in presence of magnetic field for phase transition in a neutron star

Hadronic to quark matter phase transition may occur inside neutron stars (NS) having central densities of the order of 3-10 times normal nuclear matter saturation density ($n_0$). The transition is expected to be a two-step process; transition from hadronic to 2-flavour matter and two-flavour to $β$ equilibrated charge neutral three-flavour matter. In this paper we concentrate on the first step process and solve the relativistic hydrodynamic equations for the conversion front in presence of high magnetic field. Lorentz force due to magnetic field is included in the energy momentum tensor by averaging over the polar angles. We find that for an initial dipole configuration of the magnetic field with a sufficiently high value at the surface, velocity of the front increases considerably.

astro-ph.HE↗
arXiv2011

Entropy scaling and thermalization in hadron-hadron collisions at LHC

The recent LHC data have once more brought the issue of the formation of thermalized state of matter in hadron-hadron collisions into the forefront. In this letter, we have shown that the scaling of the information entropy of the chaotically produced particles is valid up to recently available data from p+p collisions at $\sqrt{s}$ = 2.36 TeV obtained by ALICE experiment. We predict that at the highest energies projected for LHC, almost all the particles will be produced chaotically, indicating that a collective behavior should be observed in hadronic collisions, as indicated by one of present authors quite some time ago.

hep-ph↗
arXiv2011

Calibration of a solid state nuclear track detector (SSNTD) with high detection threshold to search for rare events in cosmic rays

We have investigated a commercially available polymer for its suitability as a solid state nuclear track detector (SSNTD). We identified that polymer to be polyethylene terephthalate (PET) and found that it has a higher detection threshold compared to many other widely used SSNTDs which makes this detector particularly suitable for rare event search in cosmic rays as it eliminates the dominant low Z background. Systematic studies were carried out to determine its charge response which is essential before any new material can be used as an SSNTD. In this paper we describe the charge response of PET to 129Xe, 78Kr and 49Ti ions from the REX-ISOLDE facility at CERN, present the calibration curve for PET and characterize it as a nuclear track detector.

nucl-ex↗
arXiv2009

Magnetic field inhibits the conversion of neutron stars to quark stars

Neutron stars provide a natural laboratory to test some unique implications of Quantum Chromodynamics (QCD)- the underlying theory of strong interactions- at extreme conditions of very high baryon density. It has been suggested that the true ground state of QCD is strange quark matter, and, consequently, neutron stars should convert to strange quark stars under suitable conditions. Substantial efforts have been, and are being, spent in studying the details of such conversion. In this letter, we show that the presence of high magnetic field, an essential feature of neutron stars, strongly inhibits the conversion of neutron stars to bare quark stars.

astro-ph.HE↗
arXiv2009

Study of low energy hadronic interaction models based on BESS observed cosmic ray proton and antiproton spectra at medium high altitude

We study low energy hadronic interaction models based on BESS observed cosmic ray proton and antiproton spectra at medium high altitude. Among the three popular low energy interaction models, we find that FLUKA reproduces results of BESS observations on secondary proton spectrum reasonably well over the whole observed energy range, the model UrQMD works well at relatively higher energies whereas spectrum obtained with GHEISHA differs significantly from the measured spectrum. Simulated antiproton spectrum with FLUKA, however, exhibits significant deviations from the BESS observation wheras UrQMD and GHEISHA reproduce the BESS observations within the experimental error.

astro-ph.HE↗
arXiv2008

Conversion of nuclear to 2-flavour quark matter in rotating compact stars: A general relativistic perspective

The conversion of neutron star to strange star is argued to be a two step process. The first process involves the deconfinement of nuclear to two-flavour quark matter. The GR results shows that the propagating front breaks up into fragments which propagate with different velocities along different directions. The time taken for this conversion to happen is of the order of few $ms$. This calculation indicates the inadequacy of non-relativistic (NR) or even Special Relativistic (SR) treatments for these cases.

astro-ph↗
arXiv2007

Effect of General Relativity and rotation on the energy deposition rate for $ν+ \barν \to e^+ + e^- $ inside a compact star

We have studied the $ν+ \barν \to e^+ + e^- $ energy deposition rate in a rotating compact star. This reaction is important for the study of gamma ray bursts. The General Relativistic (GR) effects on the energy deposition rate have been incorporated. We find that the efficiency of the process is larger for a rotating star. The total energy deposition rate increases by more than an order of magnitude due to rotation. The dependence of this energy deposition rate on the deformation parameter of the star has also been discussed.

astro-ph↗
arXiv2006

The conversion of Neutron star to Strange star : A two step process

The conversion of neutron matter to strange matter in a neutron star have been studied as a two step process. In the first step, the nuclear matter gets converted to two flavour quark matter. The conversion of two flavour to three flavour strange matter takes place in the second step. The first process is analysed with the help of equations of state and hydrodynamical equations, whereas, in the second process, non-leptonic weak interaction plays the main role. Velocities and the time of travel through the star of these two conversion fronts have been analysed and compared.

astro-ph↗
arXiv2006

Colour entangled orphan quarks and dark energy from cosmic QCD phase transition

The present day astrophysical observations indicate that the universe is composed of a large amount of dark energy (DE) responsible for an accelerated expansion of the universe, along with a sizeable amount of cold dark matter (CDM), responsible for structure formation. The explanations for the origin or the nature of both CDM and DE seem to require ideas beyond the standard model of elementary particle interactions. Here we show that CDM and DE both can arise from the standard principles of strong interaction physics and quantum entanglement.

hep-ph↗
arXiv2006

QCD phase transition in rotaing neutron star, Neutrino beaming and Gamma-ray bursters

We have studied the emission of neutrinos from a rotating hybrid star. We find that the emission is predominantly confined to a very small angle, provided the core of the star is in a mixed phase of quarks and hadrons and the size of such a mixed phase is small. Annihilation of neutrinos to produce gamma rays has been discussed. The estimated duration of the burst is found to be within the observational range.

astro-ph↗
arXiv2005

Cosmological dark energy from the cosmic QCD phase transition and colour entanglement

Recent astrophysical observations indicate that the universe is composed of a large amount of dark energy (DE) responsible for an accelerated expansion of the universe, along with a sizeable amount of cold dark matter (CDM), responsible for structure formation. At present, the explanations for the origin or the nature of both CDM and DE seem to require ideas beyond the standard model of elementary particle interactions. Here, for the first time, we show that CDM and DE can arise entirely from the standard principles of strong interaction physics and quantum entanglement. Quantitative agreement with the present data obtains without the need for any adjustable parameters.

hep-ph↗
arXiv2005

Strangeness, Cosmological Cold Dark Matter and Dark Energy

It is now believed that the universe is composed of a small amount of the normal luminous matter, a substantial amount of matter (Cold Dark Matter: CDM) which is non-luminous and a large amount of smooth energy (Dark Energy: DE). Both CDM and DE seem to require ideas beyond the standard model of particle interactions. In this work, we argue that CDM and DE can arise entirely from the standard principles of strong interaction physics out of the same mechanism.

astro-ph↗
arXiv2004

Rotating Twin Stars and Signature of Quark-Hadron Phase Transition

The quark hadron phase transition in a rotating compact star has been studied. The NLZ-model has been used for the hadronic sector and the MIT Bag model has been used for the quark sector. It has been found that rotating twin star (third family) solutions are obtained upto $Ω\approx 4000 s^{-1}$. Stars which are rotating faster than this limit do not show any twin star solution. A backbending in moment of inertia is also observed in the supermassive rest mass sequences. The braking index is found to diverge for a star having pure quark core.

astro-ph↗
arXiv2000

Strange quark matter in cosmic ray flux and exotic events

There have been several reports of exotic nuclear fragments, with highly unusual charge to mass ratio, in cosmic ray experiments. Although there exist experimental uncertainties which make them, at best, only candidate "exotic" events, it is important to understand what they could be, if they are eventually confirmed. Among other possible explanations, some authors have interpreted them to be lumps of strange quark matter (strangelets). A major problem with such an interpretation is that to reach the earth's surface, they must possess an unusually high penetrability through the terrestrial atmosphere. We show that a recently proposed mechanism for the propagation of strangelets through the earth's atmosphere, together with a proper account of charge capture and ionisation loss, would solve this problem. We also argue that this could lead to viable strategies for definitive detection of strange quark matter in cosmic ray flux using a ground based large area array of passive detectors.

astro-ph↗