352 research outputs found
Soft Photons from Off-shell Particles in a Hot Plasma
Considering the propagation of off-shell particles in the framework of
thermal field theory, we present the general formalism for the calculation of
the production rate of soft photons and dileptons from a hot plasma. This
approach is illustrated with an electrodynamic plasma. The photon production
rate from strongly interacting quarks in the quark-gluon plasma, which might be
formed in ultrarelativistic heavy ion collisions, is calculated in the
previously unaccessible regime of photon energies of the order of the plasma
temperature within an effective field theory incorporating dynamical chiral
symmetry breaking.Comment: 8 pages in RevTeX format, 3 figures uuencoded postscript added. Also
available by anonymous ftp at ftp://tpri6c.gsi.de/pub/phenning/qh95ga
Two regularizations - two different models of Nambu-Jona-Lasinio
Two variants of the Nambu--Jona-Lasinio model -- the model with 4-dimensional
cutoff and the model with dimensionally-analytical regularization -- are
systematically compared. It is shown that they are, in essence, two different
models of light-quark interaction. In the mean-field approximation the
distinction becomes apparent in a behavior of scalar amplitude near the
threshold. For 4-dimensional cutoff the pole term can be extracted, which
corresponds to sigma-meson. For dimensionally-analytical regularization the
singularity of the scalar amplitude is not pole, and this singularity is quite
disappeared at some value of the regularization parameter.
Still more essential distinction of these models exists in the
next-to-leading order of mean-field expansion. The calculations of meson
contributions in the quark chiral condensate and in the dynamical quark mass
demonstrate, that these contributions though their relatively smallness can
destabilize the Nambu--Jona-Lasinio model with 4-dimensional cutoff. On the
contrary, the Nambu--Jona-Lasinio model with dimensionally-analytical
regularization is stabilized with the next-to-leading order, i.e. the value of
the regularization parameter shifts to the stability region, where these
contributions decrease.Comment: 14 pages; Journal version; parameter fixing procedure is modifie
Effects of mesonic correlations in the QCD phase transition
The finite temperature phase transition of strongly interacting matter is
studied within a nonlocal chiral quark model of the NJL type coupled to a
Polyakov loop. In contrast to previous investigations which were restricted to
the mean-field approximation, mesonic correlations are included by evaluating
the quark-antiquark ring sum. For physical pion masses, we find that the pions
dominate the pressure below the phase transition, whereas above T_c the
pressure is well described by the mean-field approximation result. For large
pion masses, as realized in lattice simulations, the meson effects are
suppressed.Comment: 11 pages, 4 figures; version accepted for publication in Yad. Fiz.,
text extended, 1 figure adde
Epitaxial Lead Chalcogenides on Si for Mid-IR Detectors and Emitters Including Cavities
Lead chalcogenide (IV-VI narrow-gap semiconductor) layers on Si or BaF2(111) substrates are employed to realize two mid-infrared optoelectronic devices for the first time. A tunable resonant cavity enhanced detector is realized by employing a movable mirror. Tuning is across the 4μm to 5.5μm wavelength range, and linewidth is <0.1μm. Due to the thin (0.3μm) PbTe photodiode inside the cavity, a higher sensitivity at higher operating temperatures was achieved as compared to conventional thick photodiodes. The second device is an optically pumped vertical external-cavity surface-emitting laser with PbTe-based gain layers. It emits at ∼5μm wavelength and with output power up to 50mW pulsed, or 3mW continuous wave at 100
Chiral symmetry breaking in hot matter
This series of three lectures covers (a) a basic introduction to symmetry
breaking in general and chiral symmetry breaking in QCD, (b) an overview of the
present status of lattice data and the knowlegde that we have at finite
temperature from chiral perturbation theory. (c) Results obtained from the
Nambu--Jona-Lasinio model describing static mesonic properties are discussed as
well as the bulk thermodynamic quantities. Divergences that are observed in the
elastic quark-antiquark scattering cross-section, reminiscent of the phenomenon
of critical opalescence in light scattering, is also discussed. (d) Finally, we
deal with the realm of systems out of equilibrium, and examine the effects of a
medium dependent condensate in a system of interacting quarks.Comment: 62 LaTex pages, incorporating 23 figures. Lectures given at the
eleventh Chris-Engelbrecht Summer School in Theoretical Physics, 4-13
February, 1998, to be published by Springer Verla
Photon Production from a Quark--Gluon Plasma
In-medium interactions of a particle in a hot plasma are considered in the
framework of thermal field theory. The formalism to calculate gauge invariant
rates for photon and dilepton production from the medium is given. In the
application to a QED plasma, astrophysical consequences are pointed out. The
photon production rate from strongly interacting quarks in the quark--gluon
plasma, which might be formed in ultrarelativistic heavy ion collisions, is
calculated in the previously unaccessible regime of photon energies of the
order of the plasma temperature. For temperatures below the chiral phase
transition, an effective field theory incorporating dynamical chiral symmetry
breaking is employed, and perturbative QCD at higher temperatures. A smooth
transition between both regions is obtained. The relevance to the soft photon
problem and to high energy heavy ion experiments is discussed.Comment: Paper in ReVTeX. Figures and complete paper available via anonymous
ftp, ftp://tpri6c.gsi.de/pub/phenning/hq95ga
- scattering lengths at finite temperature in the Nambu--Jona-Lasinio model
The transition amplitude for scattering is evaluated within the SU(3)
Nambu--Jona-Lasinio model. Ordering terms according to the expansion in
leads to a box-like diagram, channel diagrams that admit scalar isoscalar
exchanges, and a channel exchange of a scalar isodoublet
that has quantum numbers corresponding to the . Both
the Pauli-Villars and O(3) regularization procedures are used to evaluate the
T=0 values of the scattering lengths and . The
finite temperature dependence is studied. We find that the variation in the
channel in the calculation of leads to a change in of a
factor of about two over the temperature range of T=150 MeV
From Monodisciplinary via Multidisciplinary to an Interdisciplinary Approach Investigating Air-Sea Interactions – a SOLAS Initiative
Understanding the physical and biogeochemical interactions and feedbacks between the ocean and atmosphere is a vital component of environmental and Earth system research. The ability to predict and respond to future environmental change relies on a detailed understanding of these processes. The Surface Ocean-Lower Atmosphere Study (SOLAS) is an international research platform that focuses on the study of ocean-atmosphere interactions, for which Future Earth is a sponsor. SOLAS instigated a collaborative initiative process to connect efforts in the natural and social sciences related to these processes, as a contribution to the emerging Future Earth Ocean Knowledge-Action Network (Ocean KAN). This is imperative because many of the recent changes in the Earth system are anthropogenic. An understanding of adaptation and counteracting measures requires an alliance of scientists from both domains to bridge the gap between science and policy. To this end, three SOLAS research areas were targeted for a case study to determine a more effective method of interdisciplinary research: valuing carbon and the ocean’s role; air-sea interactions, policy and stewardship; and, air-sea interactions and the shipping industry
Meson loop effects in the NJL model at zero and non-zero temperature
We compare two different possibilities to include meson-loop corrections in
the Nambu-Jona-Lasinio model: a strict 1/N_c-expansion in next-to-leading order
and a non-perturbative scheme corresponding to a one-meson-loop approximation
to the effective action. Both schemes are consistent with chiral symmetry, in
particular with the Goldstone theorem and the Gell-Mann-Oakes-Renner relation.
The numerical part at zero temperature focuses on the pion and the rho-meson
sector. For the latter the meson-loop-corrections are crucial in order to
include the dominant rho -> pipi-decay channel, while the standard Hartree +
RPA approximation only contains unphysical qqbar-decay channels. We find that
m_\pi, f_\pi, and quantities related to the rho-meson self-energy can
be described reasonably with one parameter set in the 1/N_c-expansion scheme,
whereas we did not succeed to obtain such a fit in the non-perturbative scheme.
We also investigate the temperature dependence of the quark condensate. Here we
find consistency with chiral perturbation theory to lowest order. Similarities
and differences of both schemes are discussed.Comment: 51 pages, 18 figures, to be published in Physics of Atomic Nuclei,
the volume dedicated to the 90th birthday of A.B. Migdal, error in Eq. 4.22
correcte
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