5,911 research outputs found
Hadron Mass Spectrum from Lattice QCD
Finite temperature lattice simulations of quantum chromodynamics (QCD) are
sensitive to the hadronic mass spectrum for temperatures below the "critical"
temperature T_c ~ 160 MeV. We show that a recent precision determination of the
QCD trace anomaly shows evidence for the existence of a large number of hadron
states beyond those known from experiment. The lattice results are well
represented by an exponentially growing hadron mass spectrum up to a
temperature T = 155 MeV. Using simple parametrizations we show how one may
estimate the total spectral weight in these yet undermined states
LPM Interference and Cherenkov-like Gluon Bremsstrahlung in Dense Matter
Gluon bremsstrahlung induced by multiple parton scattering in a finite dense
medium has a unique angular distribution with respect to the initial parton
direction. A dead-cone structure with an opening angle for gluons with fractional energy arises from the
Landau-Pomeranchuck-Migdal (LPM) interference. In a medium where the gluon's
dielectric constant is , the LPM interference pattern is shown to
become Cherenkov-like with an increased opening angle determined by the
dielectric constant . For a large dielectric
constant , the corresponding total radiative parton
energy loss is about twice that from normal gluon bremsstrahlung. Implications
of this Cherenkov-like gluon bremsstrahlung to the jet correlation pattern in
high-energy heavy-ion collisions is discussed.Comment: 4 pages in RevTEx with 1 postscript figur
Cherenkov Radiation from Jets in Heavy-ion Collisions
The possibility of Cherenkov-like gluon bremsstrahlung in dense matter is
studied. We point out that the occurrence of Cherenkov radiation in dense
matter is sensitive to the presence of partonic bound states. This is
illustrated by a calculation of the dispersion relation of a massless particle
in a simple model in which it couples to two different massive resonance
states. We further argue that detailed spectroscopy of jet correlations can
directly probe the index of refraction of this matter, which in turn will
provide information about the mass scale of these partonic bound states.Comment: 4 pages, 5 figures, revte
Elastic energy loss and longitudinal straggling of a hard jet
The elastic energy loss encountered by jets produced in deep-inelastic
scattering (DIS) off a large nucleus is studied in the collinear limit. In
close analogy to the case of (non-radiative) transverse momentum broadening,
which is dependent on the medium transport coefficient , a class of
medium enhanced higher twist operators which contribute to the non-radiative
loss of the forward light-cone momentum of the jet () are identified and
the leading correction in the limit of asymptotically high is isolated.
Based on these operator products, a new transport coefficient is
motivated which quantifies the energy loss per unit length encountered by the
hard jet. These operator products are then computed, explicitly, in the case of
a similar hard jet traversing a deconfined quark-gluon-plasma (QGP) in the
hard-thermal-loop (HTL) approximation. This is followed by an evaluation of
sub-leading contributions which are suppressed by the light-cone momentum
, which yields the longitudinal "straggling" i.e., a slight change in
light cone momentum due to the Brownian propagation through a medium with a
fluctuating color field.Comment: 5 pages, 1 figure, Revtex
Relativistic calculations of the lifetimes and hyperfine structure constants in Zn
This work presents accurate {\it ab initio} determination of the magnetic
dipole (M1) and electric quadrupole (E2) hyperfine structure constants for the
ground and a few low-lying excited states in Zn, which is one of
the interesting systems in fundamental physics. The coupled-cluster (CC) theory
within the relativistic framework has been used here in this calculations. Long
standing demands for a relativistic and highly correlated calculations like CC
can be able to resolve the disagreements among the lifetime estimations
reported previously for a few low-lying states of Zn. The role of
different electron correlation effects in the determination of these quantities
are discussed and their contributions are presented.Comment: 9 pages, 1 figure. submitted to J. Phys. B Fast Trac
On the imaginary parts and infrared divergences of two-loop vector boson self-energies in thermal QCD
We calculate the imaginary part of the retarded two-loop self-energy of a
static vector boson in a plasma of quarks and gluons of temperature T, using
the imaginary time formalism. We recombine various cuts of the self-energy to
generate physical processes. We demonstrate how cuts containing loops may be
reinterpreted in terms of interference between Order tree diagrams and
the Born term along with spectators from the medium. We apply our results to
the rate of dilepton production in the limit of dilepton invariant mass E>>T.
We find that all infrared and collinear singularities cancel in the final
result obtained in this limit.Comment: references added, typos corrected, slightly abridged, version
accepted for publication in Phys. Rev.
Mass-Radius Relationships for Solid Exoplanets
We use new interior models of cold planets to investigate the mass-radius
relationships of solid exoplanets, considering planets made primarily of iron,
silicates, water, and carbon compounds. We find that the mass-radius
relationships for cold terrestrial-mass planets of all compositions we
considered follow a generic functional form that is not a simple power law:
for up to , where and are scaled mass and radius
values. This functional form arises because the common building blocks of solid
planets all have equations of state that are well approximated by a modified
polytrope of the form .
We find that highly detailed planet interior models, including temperature
structure and phase changes, are not necessary to derive solid exoplanet bulk
composition from mass and radius measurements. For solid exoplanets with no
substantial atmosphere we have also found that: with 5% fractional uncertainty
in planet mass and radius it is possible to distinguish among planets composed
predominantly of iron or silicates or water ice but not more detailed
compositions; with ~5% uncertainty water ice planets with
water by mass may be identified; the minimum plausible planet size for a given
mass is that of a pure iron planet; and carbon planet mass-radius relationships
overlap with those of silicate and water planets due to similar zero-pressure
densities and equations of state. We propose a definition of "super Earths''
based on the clear distinction in radii between planets with significant gas
envelopes and those without.Comment: ApJ, in press, 33 pages including 16 figure
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