1,265 research outputs found
Trident pair production in strong laser pulses
We calculate the trident pair production amplitude in a strong laser
background. We allow for finite pulse duration, while still treating the laser
fields nonperturbatively in strong-field QED. Our approach reveals explicitly
the individual contributions of the one-step and two-step processes. We also
expose the role gauge invariance plays in the amplitudes and discuss the
relation between our results and the optical theorem.Comment: 4 pages, 1 .eps figure. Version 2: reference added, published versio
Master equation approach to friction at the mesoscale
At the mesoscale friction occurs through the breaking and formation of local
contacts. This is often described by the earthquake-like model which requires
numerical studies. We show that this phenomenon can also be described by a
master equation, which can be solved analytically in some cases and provides an
efficient numerical solution for more general cases. We examine the effect of
temperature and aging of the contacts and discuss the statistical properties of
the contacts for different situations of friction and their implications,
particularly regarding the existence of stick-slip.Comment: To be published in Physical Review
Energy Anomaly and Polarizability of Carbon Nanotubes
The energy of electron Fermi sea perturbed by external potential, represented
as energy anomaly which accounts for the contribution of the deep-lying states,
is analyzed for massive d = 1+1 Dirac fermions on a circle. The anomaly is a
universal function of the applied field, and is related to known
field-theoretic anomalies. We express transverse polarizability of Carbon
nanotubes via the anomaly, in a way which exhibits the universality and
scale-invariance of the response dominated by pi-electrons and qualitatively
different from that of dielectric and conducting shells. Electron band
transformation in a strong-field effect regime is predicted.Comment: 4 pg
Quarkonium formation in statistical and kinetic models
I review the present status of two related models addressing scenarios in
which the formation of heavy quarkonium states in high energy heavy ion
collisions proceed via "off-diagonal" combinations of a quark and an antiquark.
The physical process involved belongs to a general class of quark
"recombination", although technically the recombining quarks here were never
previously bound in a quarkonium state. Features of these processes relevant as
a signature of color deconfinement are discussed.Comment: 6 pages, 8 figures, based on invited plenary talk at Hard Probes
2004, Ericeira, Portugal, November 3-11, 2004, to appear in the proceeding
Quantizing Majorana Fermions in a Superconductor
A Dirac-type matrix equation governs surface excitations in a topological
insulator in contact with an s-wave superconductor. The order parameter can be
homogenous or vortex valued. In the homogenous case a winding number can be
defined whose non-vanishing value signals topological effects. A vortex leads
to a static, isolated, zero energy solution. Its mode function is real, and has
been called "Majorana." Here we demonstrate that the reality/Majorana feature
is not confined to the zero energy mode, but characterizes the full quantum
field. In a four-component description a change of basis for the relevant
matrices renders the Hamiltonian imaginary and the full, space-time dependent
field is real, as is the case for the relativistic Majorana equation in the
Majorana matrix representation. More broadly, we show that the Majorana
quantization procedure is generic to superconductors, with or without the Dirac
structure, and follows from the constraints of fermionic statistics on the
symmetries of Bogoliubov-de Gennes Hamiltonians. The Hamiltonian can always be
brought to an imaginary form, leading to equations of motion that are real with
quantized real field solutions. Also we examine the Fock space realization of
the zero mode algebra for the Dirac-type systems. We show that a
two-dimensional representation is natural, in which fermion parity is
preserved.Comment: 26 pages, no figure
BRST Hamiltonian for Bulk-Quantized Gauge Theory
By treating the bulk-quantized Yang-Mills theory as a constrained system we
obtain a consistent gauge-fixed BRST hamiltonian in the minimal sector. This
provides an independent derivation of the 5-d lagrangian bulk action. The
ground state is independent of the (anti)ghosts and is interpreted as the
solution of the Fokker-Planck equation, thus establishing a direct connection
to the Fokker-Planck hamiltonian. The vacuum state correlators are shown to be
in agreement with correlators in lagrangian 5-d formulation. It is verified
that the complete propagators remain parabolic in one-loop dimensional
regularization.Comment: 23 pages, AMS-LaTeX, 1 feynmf diagram, added 2 refs email addres
From Dimensional Reduction of 4d Spin Foam Model to Adding Non-Gravitational Fields to 3d Spin Foam Model
A Kaluza-Klein like approach for a 4d spin foam model is considered. By
applying this approach to a model based on group field theory in 4d (TOCY
model), and using the Peter-Weyl expansion of the gravitational field,
reconstruction of new non gravitational fields and interactions in the action
are found. The perturbative expansion of the partition function produces graphs
colored with su(2) algebraic data, from which one can reconstruct a 3d
simplicial complex representing space-time and its geometry; (like in the
Ponzano-Regge formulation of pure 3d quantum gravity), as well as the Feynman
graph for typical matter fields. Thus a mechanism for generation of matter and
construction of new dimensions are found from pure gravity.Comment: 11 pages, no figure, to be published in International Journal of
Geometric Methods in Modern Physic
Canonical analysis of the BCEA topological matter model coupled to gravitation in (2+1) dimensions
We consider a topological field theory derived from the Chern - Simons action
in (2+1) dimensions with the I(ISO(2,1)) group,and we investigate in detail the
canonical structure of this theory.Originally developed as a topological theory
of Einstein gravity minimally coupled to topological matter fields in (2+1)
dimensions, it admits a BTZ black-hole solutions, and can be generalized to
arbitrary dimensions.In this paper, we further study the canonical structure of
the theory in (2+1) dimensions, by identifying all the distinct gauge
equivalence classes of solutions as they result from holonomy considerations.
The equivalence classes are discussed in detail, and examples of solutions
representative of each class are constructed or identified.Comment: 17 pages, no figure
Effects of technicolor on standard model running couplings
We discuss the running couplings in the standard model, SU(3SU(2U(1, when the Higgs sector is replaced by SU(
technicolor. Particular attention is given to the running of the couplings at
momentum scales where technicolor is nonperturbative, and in this region we
apply a relativistic constituent technifermion model. This model has been
tested against the known running of the QED coupling due to nonperturbative
QCD. An understanding of this low momentum running allows the calculation of
the couplings at a higher scale, , where technicolor becomes
perturbative. We provide numerical values for the changes in the three standard
model couplings between and due to technicolor, assuming
separately ``one doublet'' and ``one family'' technicolor models. The
distinction between a running and walking technicolor coupling is also
considered.Comment: 14 pages of LaTeX, UTPT-94-
Quantum Simulation of Quantum Field Theories in Trapped Ions
We propose the quantum simulation of a fermion and an antifermion field modes
interacting via a bosonic field mode, and present a possible implementation
with two trapped ions. This quantum platform allows for the scalable add-up of
bosonic and fermionic modes, and represents an avenue towards quantum
simulations of quantum field theories in perturbative and nonperturbative
regimes.Comment: To be published in Physical Review Letter
- …