15,978 research outputs found
Theory of weakly nonlinear self sustained detonations
We propose a theory of weakly nonlinear multi-dimensional self sustained
detonations based on asymptotic analysis of the reactive compressible
Navier-Stokes equations. We show that these equations can be reduced to a model
consisting of a forced, unsteady, small disturbance, transonic equation and a
rate equation for the heat release. In one spatial dimension, the model
simplifies to a forced Burgers equation. Through analysis, numerical
calculations and comparison with the reactive Euler equations, the model is
demonstrated to capture such essential dynamical characteristics of detonations
as the steady-state structure, the linear stability spectrum, the
period-doubling sequence of bifurcations and chaos in one-dimensional
detonations and cellular structures in multi- dimensional detonations
Open String Descriptions of Space-like Singularities in Two Dimensional String Theory
The matrix model formulation of two dimensional string theory has been shown
to admit time dependent classical solutions whose closed string duals are
geodesically incomplete space-times with space-like boundaries. We investigate
some aspects of the dynamics of fermions in one such background. We show that
even though the background solution appears pathological, the time evolution of
the system is smooth in terms of open string degrees of freedom, viz. the
fermions. In particular, an initial state of fermions evolves smoothly into a
well defined final state over an infinite open string time interval, while the
time perceived by closed strings appears to end abruptly. We outline a method
of calculating fermion correlators exactly using symmetry properties. The
result for the two point function is consistent with the semiclassical picture.Comment: LaTeX 8 eps figures, referenced adde
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
- …