12,256 research outputs found
Multiple colliding electromagnetic pulses: a way to lower the threshold of pair production from vacuum
The scheme of simultaneous multiple pulse focusing on one spot naturally
arises from the structural features of projected new laser systems, such as ELI
and HiPER. It is shown that the multiple pulse configuration is beneficial for
observing pair production from vacuum under the action of sufficiently
strong electromagnetic fields. The field of the focused pulses is described
using a realistic three-dimensional model based on an exact solution of the
Maxwell equations. The pair production threshold in terms of
electromagnetic field energy can be substantially lowered if, instead of one or
even two colliding pulses, multiple pulses focused on one spot are used. The
multiple pulse interaction geometry gives rise to subwavelength field features
in the focal region. These features result in the production of extremely short
bunches.Comment: 10 pages, 4 figure
Virtual Processes and Superradiance in Spin-Boson Models
We consider spin-boson models composed by a single bosonic mode and an
ensemble of identical two-level atoms. The situation where the coupling
between the bosonic mode and the atoms generates real and virtual processes is
studied, where the whole system is in thermal equilibrium with a reservoir at
temperature . Phase transitions from ordinary fluorescence to
superradiant phase in three different models is investigated. First a model
where the coupling between the bosonic mode and the atom is via the
pseudo-spin operator is studied. Second, we investigate the
generalized Dicke model, introducing different coupling constants between the
single mode bosonic field and the environment, and for rotating
and counter-rotating terms, respectively. Finally it is considered a modified
version of the generalized Dicke model with intensity-dependent coupling in the
rotating terms. In the first model the zero mode contributes to render the
canonical entropy a negative quantity for low temperatures. The last two models
presents phase transitions, even when only Hamiltonian terms which generates
virtual processes are considered
Quantum effects with an X-ray free electron laser
A quantum kinetic equation coupled with Maxwell's equation is used to
estimate the laser power required at an XFEL facility to expose intrinsically
quantum effects in the process of QED vacuum decay via spontaneous pair
production. A 9 TW-peak XFEL laser with photon energy 8.3 keV could be
sufficient to initiate particle accumulation and the consequent formation of a
plasma of spontaneously produced pairs. The evolution of the particle number in
the plasma will exhibit non-Markovian aspects of the strong-field pair
production process and the plasma's internal currents will generate an electric
field whose interference with that of the laser leads to plasma oscillations.Comment: 4 pages, LaTeX2
Explicit Non-Abelian Monopoles and Instantons in SU(N) Pure Yang-Mills Theory
It is well known that there are no static non-Abelian monopole solutions in
pure Yang-Mills theory on Minkowski space R^{3,1}. We show that such solutions
exist in SU(N) gauge theory on the spaces R^2\times S^2 and R^1\times S^1\times
S^2 with Minkowski signature (-+++). In the temporal gauge they are solutions
of pure Yang-Mills theory on T^1\times S^2, where T^1 is R^1 or S^1. Namely,
imposing SO(3)-invariance and some reality conditions, we consistently reduce
the Yang-Mills model on the above spaces to a non-Abelian analog of the \phi^4
kink model whose static solutions give SU(N) monopole (-antimonopole)
configurations on the space R^{1,1}\times S^2 via the above-mentioned
correspondence. These solutions can also be considered as instanton
configurations of Yang-Mills theory in 2+1 dimensions. The kink model on
R^1\times S^1 admits also periodic sphaleron-type solutions describing chains
of n kink-antikink pairs spaced around the circle S^1 with arbitrary n>0. They
correspond to chains of n static monopole-antimonopole pairs on the space
R^1\times S^1\times S^2 which can also be interpreted as instanton
configurations in 2+1 dimensional pure Yang-Mills theory at finite temperature
(thermal time circle). We also describe similar solutions in Euclidean SU(N)
gauge theory on S^1\times S^3 interpreted as chains of n
instanton-antiinstanton pairs.Comment: 16 pages; v2: subsection on topological charges added, title
expanded, some coefficients corrected, version to appear in PR
Supermembrane limit of Yang-Mills theory
We consider Yang-Mills theory with super translation group in eleven
auxiliary dimensions as the structure group. The gauge theory is defined on a
direct product manifold , where is a
three-dimensional Lorentzian manifold and is a circle. We show that in
the infrared limit, when the metric on is scaled down, the Yang-Mills
action supplemented by a Wess-Zumino-type term reduces to the action of an
M2-brane.Comment: 1+6 page
Vortex mass in a superfluid at low frequencies
An inertial mass of a vortex can be calculated by driving it round in a
circle with a steadily revolving pinning potential. We show that in the low
frequency limit this gives precisely the same formula that was used by Baym and
Chandler, but find that the result is not unique and depends on the force field
used to cause the acceleration. We apply this method to the Gross-Pitaevskii
model, and derive a simple formula for the vortex mass. We study both the long
range and short range properties of the solution. We agree with earlier results
that the non-zero compressibility leads to a divergent mass. From the
short-range behavior of the solution we find that the mass is sensitive to the
form of the pinning potential, and diverges logarithmically when the radius of
this potential tends to zero.Comment: 4 page
Universal Properties of Two-Dimensional Boson Droplets
We consider a system of N nonrelativistic bosons in two dimensions,
interacting weakly via a short-range attractive potential. We show that for N
large, but below some critical value, the properties of the N-boson bound state
are universal. In particular, the ratio of the binding energies of (N+1)- and
N-boson systems, B_{N+1}/B_N, approaches a finite limit, approximately 8.567,
at large N. We also confirm previous results that the three-body system has
exactly two bound states. We find for the ground state B_3^(0) = 16.522688(1)
B_2 and for the excited state B_3^(1) = 1.2704091(1) B_2.Comment: 4 pages, 2 figures, final versio
Phase coherence in quasicondensate experiments: an ab initio analysis via the stochastic Gross-Pitaevskii equation
We perform an ab initio analysis of the temperature dependence of the phase
coherence length of finite temperature, quasi-one-dimensional Bose gases
measured in the experiments of Richard et al. (Phys. Rev. Lett. 91, 010405
(2003)) and Hugbart et al. (Eur. Phys. J. D 35, 155-163 (2005)), finding very
good agreement across the entire observed temperature range
(). Our analysis is based on the one-dimensional stochastic
Gross-Pitaevskii equation, modified to self-consistently account for
transverse, quasi-one-dimensional effects, thus making it a valid model in the
regime . We also numerically implement an
alternative identification of , based on direct analysis of the
distribution of phases in a stochastic treatment.Comment: Amended manuscript with improved agreement to experiment, following
some additional clarifications by Mathilde Hugbart and Fabrice Gerbier and
useful comments by the reviewer; accepted for publication in Physical Review
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