122 research outputs found
Necessary and sufficient condition on global optimality without convexity and second order differentiability
The main goal of this paper is to give a necessary and sufficient condition
of global optimality for unconstrained optimization problems, when the objective
function is not necessarily convex. We use Gâteaux differentiability of the objective
function and its bidual (the latter is known from convex analysis)
The first dozen years of the history of ITEP Theoretical Physics Laboratory
The theoretical investigations at ITEP in the years 1945-1958 are reviewed.
There are exposed the most important theoretical results, obtained in the
following branches of physics: 1) the theory of nuclear reactors on thermal
neutrons; 2) the hydrogen bomb project ("Tube" in USSR and "Classical Super" in
USA); 3) radiation theory; ~4) low temperature physics; 5) quantum
electrodynamics and quantum field theories; 6) parity violation in weak
interactions, the theory of -decay and other weak processes; 7) strong
interaction and nuclear physics. To the review are added the English
translations of few papers, originally published in Russian, but unknown (or
almost unknown) to Western readers.Comment: 55 pages, 5 fig
Observation of Vortex Matching Phenomena in Antidot Array of NbN Thin Film
We report vortex matching phenomenon in rectangular antidot array fabricated
on epitaxial NbN thin film. The antidot array was fabricated using Focussed Ion
Beam milling technique. The magneto-transport measurements points to a period
doubling transition at higher magnetic field for rectangular lattices. The
results are discussed within the light of several models including the
multi-vortex model, the matched lattice model and the super-matched lattice
model.Comment: Added references, modified abstract and discussions and corrected
typo-graphic errors. Accepted for proceedings of M2S-IX 2009, Tokyo (Physica
C
Spacetime and vacuum as seen from Moscow
An extended text of the talk given at the conference ``2001: A Spacetime
Odyssey'', to be published in the Proceedings of the Inaugural Conference of
the Michigan Center for Theoretical Physics, University of Michigan, Ann Arbor,
21-25 May 2001, M.J. Duff and J.T. Liu eds., World Scientific, Singapore, 2002;
and of Historical Lecture ``Vacuum as seen from Moscow'' at the CERN Summer
School, 10 August, 2001. Contents: Introduction; Pomeranchuk on vacuum; Landau
on parity, P, and combined parity, CP; Search and discovery of ; "Mirror world"; Zeldovich and cosmological term; QCD vacuum
condensates; Sakharov and baryonic asymmetry of the universe, BAU; Kirzhnits
and phase transitions; Vacuum domain walls; Monopoles, strings, instantons, and
sphalerons; False vacuum; Inflation; Brane and Bulk; Acknowledgments;
References.Comment: 17 pages, 2 figure
Magnetoresistance of Two-Dimensional Fermions in a Random Magnetic Field
We perform a semiclassical calculation of the magnetoresistance of spinless
two-dimensional fermions in a long-range correlated random magnetic field. In
the regime relevant for the problem of the half filled Landau level the
perturbative Born approximation fails and we develop a new method of solving
the Boltzmann equation beyond the relaxation time approximation. In absence of
interactions, electron density modulations, in-plane fields, and Fermi surface
anisotropy we obtain a quadratic negative magnetoresistance in the weak field
limit.Comment: 12 pages, Latex, no figures, Nordita repor
Quantum corrections to the conductivity of fermion - gauge field models: Application to half filled Landau level and high- superconductors
We calculate the Altshuler-Aronov type quantum correction to the conductivity
of charge carriers in a random potential (or random magnetic field)
coupled to a transverse gauge field. The gauge fields considered simulate the
effect of the Coulomb interaction for the fractional quantum Hall state at half
filling and for the model of high- superconducting compounds. We
find an unusually large quantum correction varying linearly or quadratically
with the logarithm of temperature, in different temperature regimes.Comment: 12 pages REVTEX, 1 figure. The figure is added and minor misprints
are correcte
Unitarity Bounds for Gauged Axionic Interactions and the Green-Schwarz Mechanism
We analyze the effective actions of anomalous models in which a
four-dimensional version of the Green-Schwarz mechanism is invoked for the
cancellation of the anomalies, and we compare it with those models in which
gauge invariance is restored by the presence of a Wess-Zumino term. Some issues
concerning an apparent violation of unitarity of the mechanism, which requires
Dolgov-Zakharov poles, are carefully examined, using a class of amplitudes
studied in the past by Bouchiat-Iliopoulos-Meyer (BIM), and elaborating on
previous studies. In the Wess-Zumino case we determine explicitly the unitarity
bound using a realistic model of intersecting branes (the Madrid model) by
studying the corresponding BIM amplitudes. This is shown to depend
significantly on the St\"uckelberg mass and on the coupling of the extra
anomalous gauge bosons and allows one to identify Standard-Model-like regions
(which are anomaly-free) from regions where the growth of certain amplitudes is
dominated by the anomaly, separated by an inflection point which could be
studied at the LHC. The bound can even be around 5-10 TeV's for a mass
around 1 TeV and varies sensitively with the anomalous coupling. The results
for the WZ case are quite general and apply to all the models in which an
axion-like interaction is introduced as a generalization of the Peccei-Quinn
mechanism, with a gauged axion.Comment: 50 pages, 28 figure
QCD sum rule for nucleon in nuclear matter
We consider the two-point function of nucleon current in nuclear matter and
write a QCD sum rule to analyse the residue of the nucleon pole as a function
of nuclear density. The nucleon self-energy needed for the sum rule is taken as
input from calculations using phenomenological NN potential. Our result shows a
decrease in the residue with increasing nuclear density, as is known to be the
case with similar quantities
Paraxial propagation of a quantum charge in a random magnetic field
The paraxial (parabolic) theory of a near forward scattering of a quantum
charged particle by a static magnetic field is presented. From the paraxial
solution to the Aharonov-Bohm scattering problem the transverse transfered
momentum (the Lorentz force) is found. Multiple magnetic scattering is
considered for two models: (i) Gaussian -correlated random magnetic
field; (ii) a random array of the Aharonov-Bohm magnetic flux line. The
paraxial gauge-invariant two-particle Green function averaged with respect to
the random field is found by an exact evaluation of the Feynman integral. It is
shown that in spite of the anomalous character of the forward scattering, the
transport properties can be described by the Boltzmann equation. The Landau
quantization in the field of the Aharonov-Bohm lines is discussed.Comment: Figures and references added. Many typos corrected. RevTex, 25 pages,
9 figure
Lowest-Landau-level theory of the quantum Hall effect: the Fermi-liquid-like state
A theory for a Fermi-liquid-like state in a system of charged bosons at
filling factor one is developed, working in the lowest Landau level. The
approach is based on a representation of the problem as fermions with a system
of constraints, introduced by Pasquier and Haldane (unpublished). This makes
the system a gauge theory with gauge algebra W_infty. The low-energy theory is
analyzed based on Hartree-Fock and a corresponding conserving approximation.
This is shown to be equivalent to introducing a gauge field, which at long
wavelengths gives an infinite-coupling U(1) gauge theory, without a
Chern-Simons term. The system is compressible, and the Fermi-liquid properties
are similar, but not identical, to those in the previous U(1) Chern-Simons
fermion theory. The fermions in the theory are effectively neutral but carry a
dipole moment. The density-density response, longitudinal conductivity, and the
current density are considered explicitly.Comment: 32 pages, revtex multicol
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