3,147 research outputs found
Vector screening masses in the quark-gluon plasma and their physical significance
Static and non-static thermal screening states that couple to the conserved
vector current are investigated in the high-temperature phase of QCD. Their
masses and couplings to the current are determined at weak coupling, as well as
using two-flavor lattice QCD simulations. A consistent picture emerges from the
comparison, providing evidence that non-static Matsubara modes can indeed be
treated perturbatively. We elaborate on the physical significance of the
screening masses.Comment: 4 pages, 3 figures. Submitted as a contribution to the proceedings of
the Quark Matter 2014 conference (talk given by H. Meyer
A relation between screening masses and real-time rates
Thermal screening masses related to the conserved vector current are
determined for the case that the current carries a non-zero Matsubara
frequency, both in a weak-coupling approach and through lattice QCD. We point
out that such screening masses are sensitive to the same infrared physics as
light-cone real-time rates. In particular, on the perturbative side, the
inhomogeneous Schrodinger equation determining screening correlators is shown
to have the same general form as the equation implementing LPM resummation for
the soft-dilepton and photon production rates from a hot QCD plasma. The static
potential appearing in the equation is identical to that whose soft part has
been determined up to NLO and on the lattice in the context of jet quenching.
Numerical results based on this potential suggest that screening masses
overshoot the free results (multiples of 2piT) more strongly than at zero
Matsubara frequency. Four-dimensional lattice simulations in two-flavour QCD at
temperatures of 250 and 340 MeV confirm the non-static screening masses at the
10% level. Overall our results lend support to studies of jet quenching based
on the same potential at T > 250 MeV.Comment: 32 pages. v2: clarifications added, typos corrected; published
versio
Epidemiological and evolutionary consequences of life-history trade-offs in pathogens
Peer reviewe
Casimir scaling of domain wall tensions in the deconfined phase of D=3+1 SU(N) gauge theories
We perform lattice calculations of the spatial 't Hooft k-string tensions in
the deconfined phase of SU(N) gauge theories for N=2,3,4,6. These equal (up to
a factor of T) the surface tensions of the domain walls between the
corresponding (Euclidean) deconfined phases. For T much larger than Tc our
results match on to the known perturbative result, which exhibits Casimir
Scaling, being proportional to k(N-k). At lower T the coupling becomes stronger
and, not surprisingly, our calculations show large deviations from the
perturbative T-dependence. Despite this we find that the behaviour proportional
to k(N-k) persists very accurately down to temperatures very close to Tc. Thus
the Casimir Scaling of the 't Hooft tension appears to be a `universal' feature
that is more general than its appearance in the low order high-T perturbative
calculation. We observe the `wetting' of these k-walls at T around Tc and the
(almost inevitable) `perfect wetting' of the k=N/2 domain wall. Our
calculations show that as T tends to Tc the magnitude of the spatial `t Hooft
string tension decreases rapidly. This suggests the existence of a (would-be)
't Hooft string condensation transition at some temperature which is close to
but below Tc. We speculate on the `dual' relationship between this and the
(would-be) confining string condensation at the Hagedorn temperature that is
close to but above Tc.Comment: 40 pages, 14 figure
CO Distribution and Kinematics Along the Bar in the Strongly Barred Spiral NGC 7479
We report on the 2.5 arcsec (400 pc) resolution CO (J = 1 -> 0) observations
covering the whole length of the bar in the strongly barred late-type spiral
galaxy NGC 7479. CO emission is detected only along a dust lane that traverses
the whole length of the bar, including the nucleus. The emission is strongest
in the nucleus. The distribution of emission is clumpy along the bar outside
the nucleus, and consists of gas complexes that are unlikely to be
gravitationally bound. The CO kinematics within the bar consist of two separate
components. A kinematically distinct circumnuclear disk, < 500 pc in diameter,
is undergoing predominantly circular motion with a maximum rotational velocity
of 245 km/s at a radius of 1 arcsec (160 pc). The CO-emitting gas in the bar
outside the circumnuclear disk has substantial noncircular motions which are
consistent with a large radial velocity component, directed inwards. The CO
emission has a large velocity gradient across the bar dust lane, ranging from
0.5 to 1.9 km/s/pc after correcting for inclination, and the projected velocity
change across the dust lane is as high as 200 km/s. This sharp velocity
gradient is consistent with a shock front at the location of the bar dust lane.
A comparison of H-alpha and CO kinematics across the dust lane shows that
although the H-alpha emission is often observed both upstream and downstream
from the dust lane, the CO emission is observed only where the velocity
gradient is large. We also compare the observations with hydrodynamic models
and discuss star formation along the bar.Comment: 16 pages, including 10 figures. Accepted for publication in Ap
String Breaking in Non-Abelian Gauge Theories with Fundamental Matter Fields
We present clear numerical evidence for string breaking in three-dimensional
SU(2) gauge theory with fundamental bosonic matter through a mixing analysis
between Wilson loops and meson operators representing bound states of a static
source and a dynamical scalar. The breaking scale is calculated in the
continuum limit. In units of the lightest glueball we find . The implications of our results for QCD are discussed.Comment: 4 pages, 2 figures; equations (4)-(6) corrected, numerical results
and conclusions unchange
Quark mass thresholds in QCD thermodynamics
We discuss radiative corrections to how quark mass thresholds are crossed, as
a function of the temperature, in basic thermodynamic observables such as the
pressure, the energy and entropy densities, and the heat capacity of high
temperature QCD. The indication from leading order that the charm quark plays a
visible role at surprisingly low temperatures, is confirmed. We also sketch a
way to obtain phenomenological estimates relevant for generic expansion rate
computations at temperatures between the QCD and electroweak scales, pointing
out where improvements over the current knowledge are particularly welcome.Comment: 14 pages. v2: minor additions and clarifications; published versio
Spatial correlators in strongly coupled plasmas
We numerically calculate the spatial correlators of the scalar and
pseudoscalar operators and , in SU(3) Yang-Mills theory at
zero and finite-temperature on the lattice. We compare the results over the
distances to the free-field prediction, to the
operator-product expansion as well as to the strongly coupled large-
\sN=4 super-Yang-Mills theory, where results are obtained by AdS/CFT methods.
For , both channels exhibit stronger spatial correlations than
in the vacuum, and we give an explanation for this, using sum-rules and the
operator-product expansion. The AdS/CFT calculation provides a
semi-quantitatively successful description of the vacuum-subtracted
correlator, renormalized in the 3-loop scheme, in the
interval of temperatures , while the free-field prediction has
the wrong sign. The and correlators are predicted to have the
same functional form both at weak coupling and in the strongly coupled SYM
theory. The Yang-Mills plasma does not meet that expectation below .
Instead we find that strong fluctuations of are present at least up
to that temperature. We discuss the impact of our results on our understanding
of the quark-gluon plasma.Comment: 32 pages, 9 figures, 4 tables; added some references, more detailed
captions, conclusions unchange
Quarkonium in Hot Medium
I review recent progress in studying quarkonium properties in hot medium as
well as possible consequences for quarkonium production in heavy ion
collisions.Comment: Invited talk at SQM 2009, Buzios, Brazil, Sep. 27 -Oct. 2 2009,
LaTeX, 8 pages,3 figures; typos corrected, references adde
Gauge Dependence of the High-Temperature 2-Loop Effective Potential for the Higgs Field
The high-temperature limit of the 2-loop effective potential for the Higgs
field is calculated from an effective 3d theory, in a general covariant gauge.
It is shown explicitly that a gauge-independent result can be extracted for the
equation of state from the gauge-dependent effective potential. The convergence
of perturbation theory is estimated in the broken phase, utilizing the gauge
dependence of the effective potential.Comment: 13 LaTeX-pages + 2 ps-figure (Instructions added to uudecode the
ps-file.
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