arXiv subjects

Jishnu Dey

Publications and source records attributed to Jishnu Dey.

48 records · Page 3Linked to original sources

arXiv1999

On the nature of the compact star in 4U 1728-34

The discovery of kilohertz quasi-periodic oscillations (kHz QPOs) in low-mass X-ray binaries (LMXBs) with the Rossi X-ray Timing Explorer has stimulated extensive studies of these sources. Recently, Osherovich & Titarchuk suggest a new model for kHz QPOs and the related correlations between kHz QPOs and low frequency features in LMXBs. Here we use their results to study the mass - radius relation for the atoll source 4U 1728-34. We find that, if this model is correct, 4U 1728-34 is possibly a strange star rather a neutron star.

astro-ph↗

arXiv1999

Magnetic Moment of the $Ω^-$ in QCD sumrule (QCDSR)

The $Ω^-$ magnetic moment was measured very accurately and experimentalists remarked that it differs from the theoretical estimates, thus posing a challenge to the latter. One such estimation uses QCDSR. We revisit this sumrule method, using condensate parameters which were obtained from fitting the differences ($μ_p - μ_n$), ($μ_{Σ^+}- μ_{Σ^-}$) and ($μ_{Ξ^0} - μ_{Ξ^-}$) and confirm the experimental number. The $μ_{Δ^{++}}$ is also found to agree with the experimental estimate.

hep-ph↗

arXiv1999

Non-linear Regge spectrum fits to experimentally up-dated meson states

The exciting feature of recent times is the inflow of new experimental data. Fits to the $π, \r$ and f meson resonances found by the VES collaboration, along with those of the PDG 1998 compilation are reported using a non-linear model for Regge trajectories. There are only five parameters including the pion mass and the states come out as Regge -type excitations of the pion. Total number of mesons fitted are 23 and the fit is good to $\sim$ 3% for 18 of them and $\sim$ 9% for others.

hep-ph↗

arXiv1999

Limiting temperature of hadrons using states predicted from kappa-deformed Poincaré algebra

The experimental hadronic density of states dN/dm, assumed to be a sum of normalized Breit- Wigner distributions and plotted as a function of the hadron mass m, fails to show a Hagedorn like growth beyond 2 GeV, probably due to a lack of data. Experimental hadronic states are fitted using $\ka$ -deformed Poincaré algebra and the fit is used to extrapolate for including states not detected. For the theoretical density of states the plot is a straight line in the log scale even beyond 2 GeV with a limiting temperature of 400 MeV.

hep-ph↗

arXiv1999

Is SAX J1808.4-3658 a Strange Star ?

One of the most important questions in the study of compact objects is the nature of pulsars, including whether they are composed of $β$-stable nuclear matter or strange quark matter. Observations of the newly discovered millisecond X-ray pulsar \sax with the Rossi X-Ray Timing Explorer place firm constraint on the radius of the compact star. Comparing the mass - radius relation of \sax with the theoretical mass - radius relation for neutron stars and for strange stars, we find that a strange star model is more consistent with SAX J1808.4-3658, and suggest that it is a likely strange star candidate.

hep-ph↗

arXiv1998

Strange Stars with Realistic Quark Vector Interaction and Phenomenological Density-dependent Scalar Potential

We derive an equation of state (EOS) for strange matter, starting from an interquark potential which (i) has asymptotic freedom built into it, (ii) shows confinement at zero baryon density and deconfinement at high density and (iii) gives a stable configuration for chargeless, beta--stable quark matter. This EOS is then used to calculate the structure of Strange Stars, and in particular their mass-radius relation. Our present results confirm and reinforce the recent claim by Li et al (Astron. and Astrophys. 303 (1995) L1) and Bombaci (Phys.Rev. C55 (1997) 1587) that the compact objects associated with the x-ray pulsar Her X-1, and with the x-ray burster 4U 1820-30 are strange stars.

astro-ph↗

arXiv1998

Uses of QCD sumrules (QCDSR) from different points of view

We support the idea that the baryon, B with mass $M_B$, couples to its current with a coupling $\la_{B}^2 \sim 0.71 M_B^6$ from an analysis of magnetic moment sum rules. And we find a sum rule among the experimental magnetic moments which is independent of the parameters of QCDSR.

hep-ph↗

arXiv1997

Scaling Law for Baryon Coupling to its Current and its possible applications

The baryon- coupling to its current ($λ_{B}$), in conventional QCD sum rule calculations (QCDSR), is shown to scale as the cubic power of the baryon mass, $M_B$. Some theoretical justification for it comes from a simple light-cone model and also general scaling arguments for QCD. But more importantly, taken as a phenomenological ansatz for the present, this may find very good use in current explorations of possible applications of QCDSR to baryon physics both at temperature $T = 0$, $T \ne 0$ and/or density $ρ= 0$, $ρ\ne 0$.

hep-ph↗

arXiv1996

QCD phase transitions from relativistic hadron models

The models of translationally invariant infinite nuclear matter in the relativistic mean field models are very interesting and simple, since the nucleon can connect only to a constant vector and scalar meson field. Can one connect these to the complicated phase transitions of QCD ? For an affirmative answer to this question, one must consider models where the coupling constants to the scalar and vector fields must depend on density in a non-linear way, since as such the models are not explicitly chirally invariant. Once this is ensured, indeed one can derive a quark condensate indirectly from the energy density of nuclear matter which goes to zero at large density and temperature. The change to zero condensate indicates a smooth phase transition.

hep-ph↗

arXiv1996

The connection between the nuclear matter mean-field equation of state and the quark and gluon condensates at high density

It is known now that chiral symmetry restoration requires the meson-nucleon coupling to be density dependent in nuclear-matter mean-field models. We further show that quite generally, the quark and gluon condensates in medium are related to the trace of energy-momentum tensor of nuclear matter and in these models the incompressibility, K, must be less than thrice the chemical potential, $μ$. In the critical density $ρ_c$, the gluon condensate is only reduced by $20\%$ indicating a larger effective nucleon mass.

hep-ph↗

arXiv1993

Observed Supersymmetry and Parity Doubling of Excited Hadrons from a Simple Spectrum-Generating Algebra

We find remarkable agreement with the observed excitations of hadrons with a simple three parameter mass relation of the SU(3) subgroup of the underlying U(15/30) graded Lie group. The baryons are the appropriate supersymmetric partners of the mesons. An interesting feature, which is a focus of current interest, is that the baryons and isobars show parity doubling. Significantly, the ground state baryons and mesons have no place in the fit, so that the parity doubling is indicated only when excitation energy is available. This has correspondence with the parity doubling seen in recent lattice calculations, when thermal excitation is present. The agreement with experiment is comparable to the semi-relativistic quark model which fits with many force parameters and where the observed parity doubling is accidental. The gross splitting of the levels is the same for the strange and the non-strange sectors, suggesting flavour independence.

hep-ph↗

arXiv1993

Problem of Statistical Model in Deep Inelastic Scattering Phenomenology

Recent Deep Inelastic data leads to an up-down quark asymmetry of the nucleon sea. Explanations of the flavour asymmetry and the di-lepton production in proton-nucleus collisions call for a temperature $T \approx 100$ MeV in a statistical model. This T may be conjectured as being due to the Fulling-Davies-Unruh effect. But it is not possible to fit the structure function itself.

hep-ph↗