380 research outputs found
Quasinormal modes and dispersion relations for quarkonium in a plasma
Recent investigations show that the thermal spectral function of heavy and vector mesons can be described using holography.
These studies consider a bottom up model that captures the heavy flavour
spectroscopy of masses and decay constants in the vacuum and is consistently
extended to finite temperature. The corresponding spectral functions provide a
picture of the dissociation process in terms of the decrease of the quasi-state
peaks with temperature.
Another related tool that provides important information about the thermal
behaviour is the analysis of the quasinormal modes. They are field solutions in
a curved background assumed to represent, in gauge/gravity duality,
quasi-particle states in a thermal medium. The associated complex frequencies
are related to the thermal mass and width. We present here the calculation of
quasinormal modes for charmonium and bottomonium using the holographic
approach. The temperature dependence of mass and thermal width are
investigated. Solutions corresponding to heavy mesons moving into the plasma
are also studied. They provide the dependence of the real and imaginary parts
of the frequency with the quasi-particle momenta, the so called dispersion
relations.Comment: V2: enlarged version with clarifications, more comparison with
previous articles and additional references included. 11 figures, 2 tables,
62 references. Version accepted for publication in JHE
Anomalous dimensions from rotating open strings in AdS/CFT
We propose a new entry within the dictionary of the AdS/CFT duality at strong
coupling: in the limit of a large spin or a large R-charge, the anomalous
dimension of the gauge theory operator dual to a semiclassical rotating string
is proportional to the string proper length. This conjecture is motivated by a
generalization to strings of the rule for computing anomalous dimensions of
massive particles and supergravity fields in the anti-de Sitter space. We show
that this proportionality holds for a rotating closed string in global AdS
space, representing a high spin operator made of fields in the adjoint
representation. It is also valid for closed strings rotating in
(representing operators with large R-charge), for closed strings with multiple
AdS spin, and for giant magnons. Based on this conjecture, we calculate the
anomalous dimension of operators made of fields in the fundamental
representation, associated with high spin mesons, and which are represented by
rotating open strings attached to probe D7-branes. The result is a logarithmic
dependence upon the spin, , similar to the
closed string case. We show that the operator properties --- anomalous
dimension and spin --- are obtained from measurements made by a local observer
in the anti-de Sitter space. For the open string case, this ensures that these
quantities are independent of the mass scale introduced by the D7-branes (the
quark mass), as expected on physical grounds. In contrast, properties of the
gauge theory states, like the energy, correspond to measurements by a gauge
theory observer and depend upon the mass scale --- once again, as expected.Comment: V2: two related references include
Bottomonium dissociation in a finite density plasma
We present a holographic description of the thermal behavior of
heavy vector mesons inside a plasma at finite temperature and density. The
meson dissociation in the medium is represented by the decrease in the height
of the spectral function peaks. In order to find a description for the
evolution of the quasi-states with temperature and chemical potential it is
crucial to use a model that is consistent with the decay constant behavior. The
reason is that the height of a spectral function peak is related to the value
of the zero temperature decay constant of the corresponding particle. AdS/QCD
holographic models are in general not consistent with the observation that
decay constants of heavy vector mesons decrease with radial excitation level.
However, it was recently shown that using a soft wall background and
calculating the correlation functions at a finite position of anti-de Sitter
space, associated with an ultraviolet energy scale, it is possible to describe
the observed behavior. Here we extend this proposal to the case of finite
temperature and chemical potential . A clear picture of the
dissociation of bottomonium states as a function of and emerges
from the spectral function. The energy scales where the change in chemical
potential leads to changes in the thermal properties of the mesons is
consistent with QCD expectations.Comment: In V3: errors in reference citations corrected. Version published in
Physics Letters B. 15 pages, 3 figure
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