12,140 research outputs found
Collisional Energy Loss of Non Asymptotic Jets in a QGP
We calculate the collisional energy loss suffered by a heavy (charm) quark
created at a finite time within a Quark Gluon Plasma (QGP) in the classical
linear response formalism as in Peigne {\it et al.} \cite{peigne}. We pay close
attention to the problem of formulating a suitable current and the isolation of
binding and radiative energy loss effects. We find that unrealistic large
binding effects arising in previous formulations must be subtracted. The finite
time correction is shown to be important only for very short length scales on
the order of a Debye length. The overall energy loss is similar in magnitude to
the energy loss suffered by a charge created in the asymptotic past. This
result has significant implications for the relative contribution to energy
loss from collisional and radiative sources and has important ramifications for
the ``single electron puzzle'' at RHIC.Comment: 15 Pages, 11 figures, revte
Comments on Black Holes in String Theory
A very brief review is given of some of the developments leading to our
current understanding of black holes in string theory. This is followed by a
discussion of two possible misconceptions in this subject - one involving the
stability of small black holes and the other involving scale radius duality.
Finally, I describe some recent results concerning quasinormal modes of black
holes in anti de Sitter spacetime, and their implications for strongly coupled
conformal field theories (in various dimensions).Comment: 13 pages. Talk given at Strings '99, Potsdam, German
Where is the Information Stored in Black Holes?
It is shown that many modes of the gravitational field exist only inside the
horizon of an extreme black hole in string theory. At least in certain cases,
the number of such modes is sufficient to account for the Bekenstein-Hawking
entropy. These modes are associated with sources which carry Ramond-Ramond
charge, and so may be viewed as the strong coupling limit of D-branes. Although
these sources naturally live at the singularity, they are well defined and
generate modes which extend out to the horizon. This suggests that the
information in an extreme black hole is not localized near the singularity or
the horizon, but extends between them.Comment: 21 pages, reference corrected and comment adde
Quenching and Tomography from RHIC to LHC
We compare fully perturbative and fully nonperturbative pictures of high-pT
energy loss calculations to the first results from LHC. While over-suppressed
compared to published ALICE data, parameter-free pQCD predictions based on the
WHDG energy loss model constrained to RHIC data simultaneously describe well
the preliminary CMS hadron suppression, ATLAS charged hadron v2, and ALICE D
meson suppression; we also provide for future reference WHDG predictions for B
meson RAA. However, energy loss calculations based on AdS/CFT also
qualitatively describe well the RHIC pion and non-photonic electron suppression
and LHC charged hadron suppression. We propose the double ratio of charm to
bottom quark RAA will qualitatively distinguish between these two energy loss
pictures.Comment: 4 pages, 3 figures. Proceedings for Quark Matter 201
Diagnosing Energy Loss: PHENIX Results on High-pT Hadron Spectra
Measurements of inclusive spectra of hadrons at large transverse momentum
over a broad range of energy in different collision systems have been performed
with the PHENIX experiment at RHIC. The data allow to study the energy and
system size dependence of the suppression observed in RAA of high-pT hadrons at
sqrt(s_NN)= 200 GeV. Due to the large energy range from sqrt(s_NN)= 22 GeV to
200 GeV, the results can be compared to results from CERN SPS at a similar
energy. The large Au+Au dataset from the 2004 run of RHIC also allows to
constrain theoretical models that describe the hot and dense matter produced in
such collisions. Investigation of particle ratios such as eta/pi0 helps
understanding the mechanisms of energy loss.Comment: 4 pages, 6 figures. To appear in the proceedings of the 19th
International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions
(Quark Matter 2006), Shanghai, China, November 14-20, 200
Evolution of near extremal black holes
Near extreme black holes can lose their charge and decay by the emission of
massive BPS charged particles. We calculate the greybody factors for low energy
charged and neutral scalar emission from four and five dimensional near
extremal Reissner-Nordstrom black holes. We use the corresponding emission
rates to obtain ratios of the rates of loss of excess energy by charged and
neutral emission, which are moduli independent, depending only on the integral
charges and the horizon potentials. We consider scattering experiments, finding
that evolution towards a state in which the integral charges are equal is
favoured, but neutral emission will dominate the decay back to extremality
except when one charge is much greater than the others. The implications of our
results for the agreement between black hole and D-brane emission rates and for
the information loss puzzle are then discussed.Comment: 25 pages, RevTe
Statistical Effects and the Black Hole/D-brane Correspondence
The horizon area and curvature of three-charge BPS black strings are studied
in the D-brane ensemble for the stationary black string. The charge
distributions along the string are used to translate the classical expressions
for the horizon area and curvature of BPS black strings with waves into
operators on the D-brane Hilbert space. Despite the fact that any `wavy' black
string has smaller horizon area and divergent curvature, the typical values of
the horizon area and effects of the horizon curvature in the D-brane ensemble
deviate negligibly from those of the original stationary black string in the
limit of large integer charges. Whether this holds in general will depend on
certain properties of the quantum bound states.Comment: 13 pages, RevTex, small errors corrected, some interpretation changed
in light of new result
Greybody factor for the BTZ black hole and a 5D black hole
We study the 5D black holes in the type IIB superstring theory compactified
on . Far from horizon, we have flat space-time. Near horizon,
we have . We calculate the
greybody factor of a minimally coupled scalar by replacing the original
geometry() by . In the
low-energy scattering, it turns out that the result agrees with the greybody
factor of the 5D black hole (or D1 + D5 branes)in the dilute gas approximation.
This confirms that the -theory() contains the
essential information about the bulk 5D black holes.Comment: some discussions are added, 15 Pages, No figure, RevTe
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