37,581 research outputs found
A path integral for heavy-quarks in a hot plasma
We propose a model for the propagation of a heavy-quark in a hot plasma, to
be viewed as a first step towards a full description of the dynamics of heavy
quark systems in a quark-gluon plasma, including bound state formation. The
heavy quark is treated as a non relativistic particle interacting with a
fluctuating field, whose correlator is determined by a hard thermal loop
approximation. This approximation, which concerns only the medium in which the
heavy quark propagates, is the only one that is made, and it can be improved.
The dynamics of the heavy quark is given exactly by a quantum mechanical path
integral that is calculated in this paper in the Euclidean space-time using
numerical Monte Carlo techniques. The spectral function of the heavy quark in
the medium is then reconstructed using a Maximum Entropy Method. The path
integral is also evaluated exactly in the case where the mass of the heavy
quark is infinite; one then recovers known results concerning the complex
optical potential that controls the long time behavior of the heavy quark. The
heavy quark correlator and its spectral function is also calculated
semi-analytically at the one-loop order, which allows for a detailed
description of the coupling between the heavy quark and the plasma collective
modes
Multiple Parton Scattering in Nuclei: Heavy Quark Energy Loss and Modified Fragmentation Functions
Multiple scattering, induced radiative energy loss and modified fragmentation
functions of a heavy quark in nuclear matter are studied within the framework
of generalized factorization in perturbative QCD. Modified heavy quark
fragmentation functions and energy loss are derived in detail with illustration
of the mass dependencies of the Landau-Pomeranchuk-Migdal interference effects
and heavy quark energy loss. Due to the quark mass dependence of the gluon
formation time, the nuclear size dependencies of nuclear modification of the
heavy quark fragmentation function and heavy quark energy loss are found to
change from a linear to a quadratic form when the initial energy and momentum
scale are increased relative to the quark mass. The radiative energy loss of
the heavy quark is also significantly suppressed due to limited cone of gluon
radiation imposed by the mass. Medium modification of the heavy quark
fragmentation functions is found to be limited to the large region due to
the form of heavy quark fragmentation functions in vacuum.Comment: 28 pages in RevTex with 20 postscript figures, final versio
Test of the heavy quark-light diquark approximation for baryons with a heavy quark
We check a commonly used approximation in which a baryon with a heavy quark
is described as a heavy quark-light diquark system. The heavy quark influences
the diquark internal motion reducing the average distance between the two light
quarks. Besides, we show how the average distance between the heavy quark and
any of the light quarks, and that between the heavy quark and the center of
mass of the light diquark, are smaller than the distance between the two light
quarks, which seems to contradict the heavy quark-light diquark picture. This
latter result is in agreement with expectations from QCD sum rules and lattice
QCD calculations. Our results also show that the diquark approximations
produces larger masses than the ones obtained in a full calculation.Comment: 9 latex pages, 5 figures, 6 table
Heavy Baryons: A Combined Large N_c and Heavy Quark Expansion for Electroweak Currents
The combined large N_c and heavy quark limit for baryons containing a single
heavy quark is discussed. The combined large N_c and heavy quark expansion of
the heavy quark bilinear operators is obtained. In the combined expansion the
corrections proportional to m_N/m_Q are summed to all orders. In particular,
the combined expansion can be used to determine semileptonic form factors of
heavy baryons in the combined limit.Comment: 8 pages. Presented at The Phenomenology of Large N_c QCD, Tempe,
Arizona, 9-11 Jan 200
Heavy Quark Diffusion and Lattice Correlators
We study charmonia correlators at finite temperature. We analyze to what
extent heavy quarkonia correlators are sensitive to the effect of heavy quark
transport and whether it is possible to constrain the heavy quark diffusion
constant by lattice calculations. Preliminary lattice calculations of quarkonia
correlators performed on anisotropic lattices show that they are sensitive to
the effect of heavy quark transport, but much detailed calculations are
required to constrain the value of the heavy quark diffusion constant.Comment: Based on talks presented on Lattice 2005, Extreme QCD 2005 and Quark
Matter 2005, 5 pages, 4 Figure
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