7,070 research outputs found
Complex saddle points in QCD at finite temperature and density
The sign problem in QCD at finite temperature and density leads naturally to
the consideration of complex saddle points of the action or effective action.
The global symmetry of the finite-density action, where
is charge conjugation and is complex conjugation,
constrains the eigenvalues of the Polyakov loop operator at a saddle point
in such a way that the action is real at a saddle point, and net color charge
is zero. The values of and at the saddle point,
are real but not identical, indicating the different free energy cost
associated with inserting a heavy quark versus an antiquark into the system. At
such complex saddle points, the mass matrix associated with Polyakov loops may
have complex eigenvalues, reflecting oscillatory behavior in color-charge
densities. We illustrate these properties with a simple model which includes
the one-loop contribution of gluons and massless quarks moving in a constant
Polyakov loop background. Confinement-deconfinement effects are modeled
phenomenologically via an added potential term depending on the Polyakov loop
eigenvalues. For sufficiently large and , the results obtained reduce
to those of perturbation theory at the complex saddle point. These results may
be experimentally relevant for the CBM experiment at FAIR.Comment: 13 pages, 3 figures. Additional references and minor revision
Femtosecond Photodissociation of Molecules Facilitated by Noise
We investigate the dynamics of diatomic molecules subjected to both a
femtosecond mid-infrared laser pulse and Gaussian white noise. The stochastic
Schr\"odinger equation with a Morse potential is used to describe the molecular
vibrations under noise and the laser pulse. For weak laser intensity, well
below the dissociation threshold, it is shown that one can find an optimum
amount of noise that leads to a dramatic enhancement of the dissociation
probability. The enhancement landscape which is shown as a function of both the
noise and the laser strength, exhibits a global maximum. A frequency-resolved
gain profile is recorded with a pump-probe set-up which is experimentally
realizable. With this profile we identify the linear and nonlinear multiphoton
processes created by the interplay between laser and noise and assess their
relative contribution to the dissociation enhancement.Comment: 5 pages,5 figure
Optimal Stochastic Enhancement of Photoionization
The effect of noise on the nonlinear photoionization of an atom due to a
femtosecond pulse is investigated in the framework of the stochastic
Schr\"odinger equation. A modest amount of white noise results in an
enhancement of the net ionization yield by several orders of magnitude, giving
rise to a form of quantum stochastic resonance. We demonstrate that this effect
is preserved if the white noise is replaced by broadband chaotic light.Comment: 4 pages, 4 figure
- …