121478460
On the density dependence of nucleon size in nuclear medium
Abstract There has been speculation regarding the increase in nucleon size in dense nuclear medium. Following recent suggestions this increase with the restoration of chiral symmetry at high density is estimated. A measure of symmetry breaking is the pion decay constant, ƒ π and its density dependence is extractedfrom QCD sum rules. The nucleon size is inversely proportional to ƒ π .
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.
13958309
Evidence for strange stars from joint observation of harmonic absorption bands and of redshift
From recent reports on terrestrial heavy ion collision experiments it appears that one may not obtain information about the existence of asymptotic freedom (AF) and chiral symmetry restoration (CSR) for quarks of QCD at high density. This information may still be obtained from compact stars – if they are made up of strange quark matter (SQM). 
 
 
 
Very high gravitational redshift lines (GRL), seen from some compact stars, seem to suggest high ratios of mass and radius (M/R) for them. This is suggestive of strange stars (SS) and can in fact be fitted very well with SQM equation of state (EOS) deduced with built in AF and CSR. In some other stars broad absorption bands (BAB) appear at about ∼0.3 keV and multiples thereof, that may fit in very well with resonance with harmonic compressional breathing mode frequencies of these SS. Emission at these frequencies are also observed in six stars. 
 
 
 
If these two features of large GRL and BAB were observed together in a single star, it would strengthen the possibility for the existence of SS in nature and would vindicate the current dogma of AF and CSR that we believe in QCD. Recently, in 4U 1700 − 24, both features appear to be detected, which may well be interpreted as observation of SS – although the group that analyzed the data did not observe this possibility. We predict that if the shifted lines, that has been observed, are from neon with GRL shift z= 0.4– then the compact object emitting it is a SS of mass 1.2 M⊙ and radius 7 km. In addition the fit to the spectrum leaves a residual with broad dips at 0.35 keV and multiples thereof, as in 1E 1207 − 5209 which is again suggestive of SS.
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.
15400142
Strange Stars : An interesting member of the compact object family
We have studied strange star properties both at zero temperature and at finite temperatures and searched signatures of strange stars in gamma‐ray, x‐ray and radio astronomy. We have a set of Equations of State (EoS) for strange quark matter (SQM) and solving the TOV equations, we get the structure of strange stars. The maximum mass for a strange star decreases with the increase of temperature, because at high temperatures, the EoS become softer. One important aspect of strange star is that, surface tension depends on the size and structure of the star and is significantly larger than the conventional values. Moment of inertia is another important parameter for compact stars as by comparing theoretical values with observed estimate, it is possible to constrain the dense matter Equation of State. We hope that this approach will help us to decide whether the members of the double pulsar system PSR J0737‐3039 are neutron stars or strange stars.
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.
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.
109094861
Modification of Linac 7651 driver to operate at 425 MHz