55,468 research outputs found
Brane Cosmologies without Orbifolds
We study the dynamics of branes in configurations where 1) the brane is the
edge of a single anti-de Sitter (AdS) space and 2) the brane is the surface of
a vacuum bubble expanding into a Schwarzschild or AdS-Schwarzschild bulk. In
both cases we find solutions that resemble the standard Robertson-Walker
cosmologies although in the latter, the evolution can be controlled by a mass
parameter in the bulk metric. We also include a term in the brane action for
the scalar curvature. This term adds a contribution to the low energy theory of
gravity which does not need to affect the cosmology but which is necessary for
the surface of the vacuum bubble to recover four dimensional gravity.Comment: 13 pages, uses harvmac, vacuum bubble case corrected and expanded,
references adde
Random quantum channels I: graphical calculus and the Bell state phenomenon
This paper is the first of a series where we study quantum channels from the
random matrix point of view. We develop a graphical tool that allows us to
compute the expected moments of the output of a random quantum channel. As an
application, we study variations of random matrix models introduced by Hayden
\cite{hayden}, and show that their eigenvalues converge almost surely. In
particular we obtain for some models sharp improvements on the value of the
largest eigenvalue, and this is shown in a further work to have new
applications to minimal output entropy inequalities.Comment: Several typos were correcte
Regularization Schemes and Higher Order Corrections
I apply commonly used regularization schemes to a multi-loop calculation to
examine the properties of the schemes at higher orders. I find complete
consistency between the conventional dimensional regularization scheme and
dimensional reduction, but I find that the four dimensional helicity scheme
produces incorrect results at next-to-next-to-leading order and singular
results at next-to-next-to-next-to-leading order. It is not, therefore, a
unitary regularization scheme.Comment: References added and typographical errors correcte
The Four Dimensional Helicity Scheme Beyond One Loop
I describe a procedure by which one can transform scattering amplitudes
computed in the four dimensional helicity scheme into properly renormalized
amplitudes in the 't Hooft-Veltman scheme. I describe a new renormalization
program, based upon that of the dimensional reduction scheme and explain how to
remove both finite and infrared-singular contributions of the evanescent
degrees of freedom to the scattering amplitude.Comment: 20 page
Collisional-dissociative recombination of electrons with molecular ions
Recombination rate calculation of electrons in plasma having ions of molecules with both repulsive and bound neutral state
The space-time structure of hard scattering processes
Recent studies of exclusive electroproduction of vector mesons at JLab make
it possible for the first time to play with two independent hard scales: the
virtuality Q^2 of the photon, which sets the observation scale, and the
momentum transfer t to the hadronic system, which sets the interaction scale.
They reinforce the description of hard scattering processes in terms of few
effective degrees of freedom relevant to the Jlab-Hermes energy range.Comment: 4 pages; 5 figure
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