26 research outputs found
Spectral functions in the sigma-channel near the critical end point
Spectral functions in the -channel are investigated near the chiral
critical end point (CEP), that is, the point where the chiral phase transition
ceases to be first-ordered in the -plane of the QCD phase diagram. At
that point the meson becomes massless in spite of explicit breaking of
the chiral symmetry. It is expected that experimental signatures peculiar to
CEP can be observed through spectral changes in the presence of abnormally
light mesons. As a candidate, the invariant-mass spectrum for diphoton
emission is estimated with the chiral quark model incorporated. The results
show the characteristic shape with a peak in the low energy region, which may
serve as a signal for CEP. However, we find that the diphoton multiplicity is
highly suppressed by infrared behaviors of the meson. Experimentally,
in such a low energy region below the threshold of two pions, photons from
are major sources of the background for the signal.Comment: 12 pages, 8 figures, 1 figure replaced, minor modification
Scalar density fluctuation at critical end point in NJL model
Soft mode near the critical end point in the phase diagram of two-flavor
Nambu--Jona-Lasinio (NJL) model is investigated within the leading 1/N_c
approximation with N_c being the number of the colors. It is explicitly shown
by studying the spectral function of the scalar channel that the relevant soft
mode is the scalar density fluctuation, which is coupled with the quark number
density, while the sigma meson mode stays massive.Comment: 9 pages, 4 figure
Radial Velocity Studies of Close Binary Stars.VI
Radial-velocity measurements and sine-curve fits to the orbital velocity
variations are presented for the sixth set of ten close binary systems: SV Cam,
EE Cet, KR Com, V410 Cyg, GM Dra, V972 Her, ET Leo, FS Leo, V2388 Oph, II UMa.
All systems except FS Leo are double-lined spectroscopic binaries. The type of
FS Leo is unknown while SV Cam is a close, detached binary; all remaining
systems are contact binaries. Eight binaries (all except SV Cam and V401 Cyg)
are the recent photometric discoveries of the Hipparcos satellite project. Five
systems, EE Cet, KR Com, V401 Cyg, V2388 Oph, II UMa, are members of
visual/spectroscopic triple systems. We were able to observe the close binary
system EE Cet separately of its companion, but in the remaining four systems we
could separate the spectral components only through the use of the
broadening-function approach. Several of the studied systems are prime
candidates for combined light and radial-velocity synthesis solutions.Comment: AASTeX5, 5 figures, 2 tables, modified after the AJ revie
Flux tube dynamics in the dual superconductor
We study plasma oscillations in a flux tube of the dual superconductor model
of 't Hooft and Mandelstam. A magnetic condensate is coupled to an
electromagnetic field by its dual vector potential, and fixed electric charges
set up a flux tube. An electrically charged fluid (a quark plasma) flows in the
tube and screens the fixed charges via plasma oscillations. We investigate both
Type I and Type II superconductors, with plasma frequencies both above and
below the threshold for radiation into the Higgs vacuum. We find strong
radiation of electric flux into the superconductor in all regimes, and argue
that this invalidates the use of the simplest dual superconductor model for
dynamical problems.Comment: 25 pages Revtex with 11 EPS figure
The O(N) linear sigma model at finite temperature beyond the Hartree approximation
We study the O(N) linear sigma model with spontaneous symmetry breaking,
using a Hartree-like ansatz with a classical field and variational masses. We
go beyond the Hartree approximation by including the two-loop contribution, the
sunset diagram, using the 2PPI expansion. We have computed numerically the
effective potential at finite temperature. We find a phase transition of second
order, while it is first order in the Hartree approximation. We also discuss
some implications of the fact that in this order, the decay of the sigma into
two pions affects the thermal diagrams.Comment: 22 pages, 14 figures. v2: minor corrections, some more references.
v3: added new set of data, new appendix. Submitted to Phys.Rev.
"Inter-Longitude Astronomy" (ILA) project : current highlights and perspectives : I. Magnetic vs. non-magneticinteracting binary stars
We present a review of highlights of our photometric and photo-polarimetric monitoring and mathematical modeling of interacting binary stars of different types classical, asynchronous, intermedi ate polars with 25 timescales corresponding to differ ent physical mechanisms and their combinations (part "Polar"); negative and positive superhumpers in nova-like and dwarf novae stars ("Superhumper"); symbiotic ("Symbiosis"); eclipsing variables with and without ev idence for a current mass transfer ("Eclipser") with a special emphasis on systems with a direct impact of the stream into the gainor star's atmosphere, which we propose to call "Impactors", or V361 Lyr-type stars. Other parts of the ILA project are "Stellar Bell" (pul sating variables of different types and periods - M, SR, RV Tau, RR Lyr, Delta Sct) and "New Variable".
Chiral Symmetry and light resonances in hot and dense matter
We present a study of the scattering amplitude in the and
channels at finite temperature and nuclear density within a chiral
unitary framework. Meson resonances are dynamically generated in our approach,
which allows us to analyze the behavior of their associated scattering poles
when the system is driven towards chiral symmetry restoration. Medium effects
are incorporated in three ways: (a) by thermal corrections of the unitarized
scattering amplitudes, (b) by finite nuclear density effects associated to a
renormalization of the pion decay constant, and complementarily (c) by
extending our calculation of the scalar-isoscalar channel to account for finite
nuclear density and temperature effects in a microscopic many-body
implementation of pion dynamics. Our results are discussed in connection with
several phenomenological aspects relevant for nuclear matter and Heavy-Ion
Collision experiments, such as mass scaling vs broadening from dilepton
spectra and chiral restoration signals in the channel. We also
elaborate on the molecular nature of resonances.Comment: 14 pages, 14 figures. Contribution to Hard Probes 2008, Illa de A
Toxa, Spain, June 8th-14th 200
A search for periodic and quasi-periodic photometric behavior in the cataclysmic variable TT arietis
Observations of TT Ari obtained at 11 observatories (campaign TT Ari-94) during 258 hr were carried out to study optical variability on timescales from minutes to weeks. The best-fit primary photometric period determined from 16 nights of data obtained at the Dushak-Eregdag station of the Odessa State University is P = 0d.133160 ± 0d.000004 with a mean amplitude of 0.0513 ± 0.0008 mag. This new primary photometric period is larger than that obtained during the TT Ari-88 campaign and is well outside the range of estimates published since 1961. Contrary to previous findings, the "5-7 hr" secondary photometric period is not seen. Our observations do show evidence for periods of 2d.916 and 0d.3040 with amplitudes of 43 and 25 mmag, respectively. The beat period between the spectroscopic and photometric periods is not seen. No coherent oscillations in the range f = 10-2500 cycles day-1 are found. The highest peaks in the power spectrum cover the wide range of 24-139 cycles day-1. In the mean periodogram, the highest peak corresponds to 21 and 30 minutes for the largest sets of observations, i.e., those obtained at Odessa and Krakow Universities, respectively. In the instrumental B system, variations with an amplitude exceeding 0.011 mag occur 8 times (from 33 runs) at 24 minutes. We conclude that quasi-periodic variations occur at a few preferred timescales rather than at a relatively stable period with a secular decrease. In the frequency range 90-900 cycles day-1, the power spectrum obeys a power law with a slope ranging from γ = 1.3 to 2.6 for different runs