1,282 research outputs found
On the mixing property for a class of states of relativistic quantum fields
Let be a factor state on the quasi-local algebra of
observables generated by a relativistic quantum field, which in addition
satisfies certain regularity conditions (satisfied by ground states and the
recently constructed thermal states of the theory). We prove that
there exist space and time translation invariant states, some of which are
arbitrarily close to in the weak* topology, for which the time
evolution is weakly asymptotically abelian
Electromagnetic vertex function of the pion at T > 0
The matrix element of the electromagnetic current between pion states is
calculated in quenched lattice QCD at a temperature of . The
nonperturbatively improved Sheikholeslami-Wohlert action is used together with
the corresponding improved vector current. The electromagnetic
vertex function is extracted for pion masses down to and
momentum transfers .Comment: 17 pages, 8 figure
The transition temperature in QCD
We present a detailed calculation of the transition temperature in QCD with
two light and one heavier (strange) quark mass on lattices with temporal extent
N_t =4 and 6. Calculations with improved staggered fermions have been performed
for various light to strange quark mass ratios in the range, 0.05 <= m_l/m_s <=
0.5, and with a strange quark mass fixed close to its physical value. From a
combined extrapolation to the chiral (m_l -> 0) and continuum (aT = 1/N_t -> 0)
limits we find for the transition temperature at the physical point T_c r_0 =
0.457(7) where the scale is set by the Sommer-scale parameter r_0 defined as
the distance in the static quark potential at which the slope takes on the
value, (dV_qq(r)/dr)_r=r_0 = 1.65/r_0^2. Using the currently best known value
for r_0 this translates to a transition temperature T_c = 192(7)(4)MeV. The
transition temperature in the chiral limit is about 3% smaller. We discuss
current ambiguities in the determination of T_c in physical units and also
comment on the universal scaling behavior of thermodynamic quantities in the
chiral limit.Comment: 18 pages, 14 EPS figures, replaced wrong entries in column 7 of Table
A.
Field dependence of magnetization reversal by spin transfer
We analyse the effect of the applied field (Happl) on the current-driven
magnetization reversal in pillar-shaped Co/Cu/Co trilayers, where we observe
two different types of transition between the parallel (P) and antiparallel
(AP) magnetic configurations of the Co layers. If Happl is weaker than a rather
small threshold value, the transitions between P and AP are irreversible and
relatively sharp. For Happl exceding the threshold value, the same transitions
are progressive and reversible. We show that the criteria for the stability of
the P and AP states and the experimentally observed behavior can be precisely
accounted for by introducing the current-induced torque of the spin transfer
models in a Landau-Lifschitz-Gilbert equation. This approach also provides a
good description for the field dependence of the critical currents
Role of the Nuclear and Electromagnetic Interactions in the Coherent Dissociation of the Relativistic Li Nucleus into the H + He Channel
The differential cross section in the transverse momentum and a total
cross section of mb for the coherent dissociation of a 3-A-GeV/
Li nucleus through the HHe channel have been measured on emulsion
nuclei. The observed dependence of the cross section is explained by the
predominant supposition of the nuclear diffraction patterns on light (C, N, O)
and heavy (Br, Ag) emulsion nuclei. The contributions to the cross section from
nuclear diffraction ( MeV/) and Coulomb MeV/)
dissociations are calculated to be 40.7 and 4 mb, respectively.Comment: ISSN 0021-3640, Pleiades Publishing, Ltd., 200
Towards a Realistic Equation of State of Strongly Interacting Matter
We consider a relativistic strongly interacting Bose gas. The interaction is
manifested in the off-shellness of the equilibrium distribution. The equation
of state that we obtain for such a gas has the properties of a realistic
equation of state of strongly interacting matter, i.e., at low temperature it
agrees with the one suggested by Shuryak for hadronic matter, while at high
temperature it represents the equation of state of an ideal ultrarelativistic
Stefan-Boltzmann gas, implying a phase transition to an effectively weakly
interacting phase.Comment: LaTeX, figures not include
The QCD Equation of State with almost Physical Quark Masses
We present results on the equation of state in QCD with two light quark
flavors and a heavier strange quark. Calculations with improved staggered
fermions have been performed on lattices with temporal extent Nt =4 and 6 on a
line of constant physics with almost physical quark mass values; the pion mass
is about 220 MeV, and the strange quark mass is adjusted to its physical value.
High statistics results on large lattices are obtained for bulk thermodynamic
observables, i.e. pressure, energy and entropy density, at vanishing quark
chemical potential for a wide range of temperatures, 140 MeV < T < 800 MeV. We
present a detailed discussion of finite cut-off effects which become
particularly significant for temperatures larger than about twice the
transition temperature. At these high temperatures we also performed
calculations of the trace anomaly on lattices with temporal extent Nt=8.
Furthermore, we have performed an extensive analysis of zero temperature
observables including the light and strange quark condensates and the static
quark potential at zero temperature. These are used to set the temperature
scale for thermodynamic observables and to calculate renormalized observables
that are sensitive to deconfinement and chiral symmetry restoration and become
order parameters in the infinite and zero quark mass limits, respectively.Comment: 22 pages, 17 EPS-figures; revised version, updated references, data
added in Tab.1, several smaller change
Radial Velocity Studies of Close Binary Stars. IX
Radial-velocity measurements and sine-curve fits to the orbital velocity
variations are presented for the eighth set of ten close binary systems: AB
And, V402 Aur, V445 Cep, V2082 Cyg, BX Dra, V918 Her, V502 Oph, V1363 Ori, KP
Peg, V335 Peg. Half of the systems (V445 Cep, V2082 Cyg, V918 Her, V1363 Ori,
V335 Peg) were discovered photometrically by the Hipparcos mission and all
systems are double-lined (SB2) contact binaries. The broadening function method
permitted improvement of the orbital elements for AB And and V502 Oph. The
other systems have been observed for radial velocity variations for the first
time; in this group are five bright (V<7.5) binaries: V445 Cep, V2082 Cyg, V918
Her, KP Peg and V335 Peg. Several of the studied systems are prime candidates
for combined light and radial-velocity synthesis solutions.Comment: 17+ pages, 2 tables, 4 figure
Scalar Mesons in a Chiral Quark Model with Glueball
Ground-state scalar isoscalar mesons and a scalar glueball are described in a
U(3)xU(3) chiral quark model of the Nambu--Jona-Lasinio (NJL) type with 't
Hooft interaction. The latter interaction produces singlet-octet mixing in the
scalar and pseudoscalar sectors. The glueball is introduced into the effective
meson Lagrangian as a dilaton on the base of scale invariance. The mixing of
the glueball with scalar isoscalar quarkonia and amplitudes of their decays
into two pseudoscalar mesons are shown to be proportional to current quark
masses, vanishing in the chiral limit. Mass spectra of the scalar mesons and
the glueball and their main modes of strong decay are described.Comment: 10 pages, LaTeX text, requires svjour.cls and svepj.cl
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