119179229
KHz QPOs in LMXBs, relations between different frequencies and compactness of stars.
Abstract We suggest that the mass of four compact stars SAX J1808.4-3658, KS 1731-260, SAX J1750.8-2900 and IGR J17191-2821 can be determined from the difference in the observed kiloHertz quasi periodic oscillations (kHz QPO-s) of these stars. The stellar radius is very close to the marginally stable orbit Rms as predicted by Einstein’s general relativity. It may be noted that the first of these stars was suggested to be a strange star more than a decade back by Li et al. (1999a) from the unique millisecond X-ray pulsations with an accurate determination of its rotation period. It showed kHz QPO-s eight years back and so far it is the only set that has been observed. This is the first time we give an estimate of the mass of the star and of three other compact stars in low-mass X-ray binaries using their observed kHz QPO-s.
15993375
Double neutron stars as double strange stars
Double neutron star systems lead to strong tests of general r lativity. The history of the double pulsar PSR J0737−3039 is also very interesting. There are claims that the youn ger member of this binary (pulsar B) had a light progenitor. It is possible that such double pulsar systems are double str ange stars. We suggest that the collapse of the light progeni tor was a phase transition to strange matter and J0737 −3039B is a strange star. This would support small baryon loss implied by the small natal kick velocity for the system J0737 −3039. Using equation of states for strange quark matter and n eutron matter, we have calculated the stellar structure and the baryon conten t of the progenitor as well as the existing star to compare wi th observational predictions. We have also calculated the moment of i ertia using both of the equation of states to facilitate co mparison with expected future measurements. The baryon number of the progenitor turns out to be ∼ 2× 1057 and with small baryon loss the this fits into a strange star of mass 1.25 M⊙. Double neutron stars may be double strange stars. If the mom ent of inertia of these stars are found in the near future as expected, then our predictions can be further tested.
127351407
Color Singlet Hadron Formation and Phase Transition to Quark - Gluon Plasma in the Bag Model
14202199
Entropy and equation of state for dense hot quark matter and its effect on compact quark stars
Dey et al. [1] derived an equation of state (EOS) for matter in strange stars (SS from hereon) with quark masses showing chiral symmetry restoration (CSM) and an interquark potential which (i) has asymptotic freedom built into it, (ii) shows confinement at zero density (ρB = 0) and deconfinement at high ρB. This EOS gives a stable configuration for chargeless, β-stable quark matter. The SS derived from this EOS fits into the empirical mass -radius (M-R) relations of some stars constraining the CSM parameters [1, 2, 3]. In the present paper we extend the calculation to include high temperatures upto T = 10 MeV ≡ 1.16 × 10 K where the quark gas is still degenerate and find that the empirical M-R relation, derived from astrophysical data, is still satisfied. The EOS is tabulated for T = 10 MeV . The entropy is calculated and matches onto that calculated from hadronic models thus supporting the idea that the quark-hadron transition may be continuous. (1) Dept. of Physics, Presidency College, Calcutta 700 073, India (2) Azad Physics Centre, Dept. of Physics, Maulana Azad College, Calcutta 700 013, India (3) Abdus Salam ICTP, Trieste, Italy (4) Department of Physics, Burdwan University, Burdwan 713104, India. † permanent address; 1/10 Prince Golam Md. Road, Calcutta 700 026, India, e-mail : deyjm@giascl01.vsnl.net.in ** Suported by DST Grant no. SP/S2/K18/96, Govt. of India.
120924061
IS THERE A SPIN 1/2 WEAK DOUBLET OF SKYRMIONS ALMOST DEGENERATE WITH W AND Z?
120717106
QCD — MOTIVATED QUARK STARS IN THE LIGHT OF RECENT ASTROPHYSICAL OBSERVATIONS
Are there quark stars in nature? We review the question in the light of modern astrophysical observations. Quark stars have properties which are very similar to those of neutron stars. For example they are now known to have the same kind of cooling properties. Their masses may also be similar. On the other hand, gamma ray bursts (GRB), the brightest phenomenon observable at present in the sky, could possibly be conversion of normal or neutron matter on the surface of a quark star. The best observational evidence for the existence of quark stars seems to be some compact objects, the X-Ray burst source 4U 1820-30, the X-ray pulsar Her X-1, the star 4U 1728-34 and SAX J-1808.4-3658, this last one being the stablest and fastest rotating hard X-ray pulsar known to date. The mass of at least these four objects is high and their radius is low, placing them close to the black hole line, in the mass–radius (M–R) plot.
36506128
Experimental Test of a New Antiproton Acceleration Scheme in the Fermilab Main Injector
In an effort to provide higher intensity and lower emittance antiproton beam to the Tevatron collider for high luminosity operation, a new Main Injector (MI) antiproton acceleration scheme has been developed [1-4]. In this scheme, beam is accelerated from 8 to 27 GeV using the 2.5 MHz rf system and from 27 to 150 GeV using the 53 MHz rf system. This paper reports the experimental results of beam study. Simulation results are reported in a different PAC’ 05 paper [5]. Experiments are conducted with proton beam from the Booster. Acceleration efficiency, emittance growth and beam harmonic transfer between 2.5 MHz (h=28) and 53 MHz (h=588) buckets have been studied. Beam study shows that one can achieve an overall acceleration efficiency of about 100%, longitudinal emittance growth less than 20% and negligible transverse emittance growth.
111241112
Linearization of the Fermilab recycler high level RF
In studying the recycler high level RF, it was found that at 89 kHz, the lowest frequency required by the system, some nonlinearities in magnitude and phase were discovered. The visible evidence of this was that beam injected in a barrier bucket had a definite slope at the top. Using a network analyzer, the S-parameter S/sub 21/ was realized for the overall system and from mathematical modeling a second order numerator and denominator transfer function was found. The inverse of this transfer function gives our linearization transfer function. The linearization transfer function was realized in hardware by summing a high pass, band pass and low pass filter together. The resulting magnitude and phase plots, along with actual beam response will be shown.