4,051 research outputs found
Slow Dynamics in Glasses
Minimalist theories of complex systems are broadly of two kinds: mean-field
and axiomatic. So far all theories of complex properties absent from simple
systems and intrinsic to glasses are axiomatic. Stretched Exponential
Relaxation (SER) is the prototypical complex temporal property of glasses,
discovered by Kohlrausch 150 years ago, and now observed almost universally in
microscopically homogeneous, complex non-equilibrium materials, including
luminescent electronic (Coulomb) glasses. Critical comparison of alternative
axiomatic theories with both numerical simulations and experiments strongly
favors dynamical trap models over static percolative or energy landscape
models.
PACS: 61.20.Lc; 67.40.F
Perturbative Analysis of Nonabelian Aharonov-Bohm Scattering
We perform a perturbative analysis of the nonabelian Aharonov-Bohm problem to
one loop in a field theoretic framework, and show the necessity of contact
interactions for renormalizability of perturbation theory. Moreover at critical
values of the contact interaction strength the theory is finite and preserves
classical conformal invariance.Comment: 12 pages in LaTeX, uses epsf.sty, 5 uuencoded Postscript figures sent
separately. MIT-CTP-228
Holographic Nuclear Physics
We analyze the phases of the Sakai-Sugimoto model at finite temperature and
baryon chemical potential. Baryonic matter is represented either by 4-branes in
the 8-branes or by strings stretched from the 8-branes to the horizon. We find
the explicit configurations and use them to determine the phase diagram and
equation of state of the model. The 4-brane configuration (nuclear matter) is
always preferred to the string configuration (quark matter), and the latter is
also unstable to density fluctuations. In the deconfined phase the phase
diagram has three regions corresponding to the vacuum, quark-gluon plasma, and
nuclear matter, with a first-order and a second-order phase transition
separating the phases. We find that for a large baryon number density, and at
low temperatures, the dominant phase has broken chiral symmetry. This is in
qualitative agreement with studies of QCD at high density.Comment: 27 pages, 26 figures. v2: Added a comment about higher derivative
corrections to the DBI action in the smeared instanton in section 2.1. v3:
References added, version published in JHEP. v4: misprints correcte
ABJM with Flavors and FQHE
We add fundamental matters to the N=6 Chern-Simons theory (ABJM theory), and
show that D6-branes wrapped over AdS_4 x S^3/Z_2 in type IIA superstring theory
on AdS_4 x CP^3 give its dual description with N=3 supersymmetry. We confirm
this by the arguments based on R-symmetry, supersymmetry, and brane
configuration of ABJM theory. We also analyze the fluctuations of the D6-brane
and compute the conformal dimensions of dual operators. In the presence of
fractional branes, the ABJM theory can model the fractional quantum Hall effect
(FQHE), with RR-fields regarded as the external electric-magnetic field. We
show that an addition of the flavor D6-brane describes a class of fractional
quantum Hall plateau transition.Comment: 23 pages, Latex, no figures; (v2) references added, typos correcte
Моделювання динамічних силових характеристик плунжерних токарних патронів з компенсаторами відцентрових сил
Efficient energy transfer was demonstrated in the SrF2:Eu2+, Pr3+ phosphor synthesized by the co-precipitation method. Results obtained with X-ray diffraction (XRD), scanning electron microscopy (SEM), x-ray spectroscopy (XPS), photoluminescence (PL) and decay curves proposed the UV-Vis energy transfer process. The energy transfer process between the Eu2+ and Pr3+ ions in SrF2 was investigated to evaluate the potential of the Eu2+ ion as a sensitizer for the Pr3+ ion. The results proposed that Eu2+ could be a good sensitizer for absorbing the UV photons and efficiently enhancing the Pr3+ emission intensity. The energy transfer process was effective until concentration quenching for the Pr3+ ions occurred. The concentration quenching was attributed to cross-relaxation between the Pr3+ ions. (C) 2016 Author(s).Funding Agencies|South African Research Chairs Initiative of the Department of Science and Technology; National Research Foundation of South Africa; National Research Foundation (NRF); Cluster program of the University of the Free State</p
Analytical results on quantum interference and magnetoconductance for strongly localized electrons in a magnetic field: Exact summation of forward-scattering paths
We study quantum interference effects on the transition strength for strongly
localized electrons hopping on 2D square and 3D cubic lattices in the presence
of a magnetic field B. These effects arise from the interference between phase
factors associated with different electron paths connecting two distinct sites.
For electrons confined on a square lattice, with and without disorder, we
obtain closed-form expressions for the tunneling probability, which determines
the conductivity, between two arbitrary sites by exactly summing the
corresponding phase factors of all forward-scattering paths connecting them. An
analytic field-dependent expression, valid in any dimension, for the
magnetoconductance (MC) is derived. A positive MC is clearly observed when
turning on the magnetic field. In 2D, when the strength of B reaches a certain
value, which is inversely proportional to twice the hopping length, the MC is
increased by a factor of two compared to that at zero field. We also
investigate transport on the much less-studied and experimentally important 3D
cubic lattice case, where it is shown how the interference patterns and the
small-field behavior of the MC vary according to the orientation of B. The
effect on the low-flux MC due to the randomness of the angles between the
hopping direction and the orientation of B is also examined analytically.Comment: 24 pages, RevTeX, 8 figures include
Perturbative Expansion in the Galilean Invariant Spin One-Half Chern-Simons Field Theory
A Galilean Chern-Simons field theory is formulated for the case of two
interacting spin-1/2 fields of distinct masses M and M'. A method for the
construction of states containing N particles of mass M and N' particles of
mass M' is given which is subsequently used to display equivalence to the
spin-1/2 Aharonov-Bohm effect in the N = N' =1 sector of the model. The latter
is then studied in perturbation theory to determine whether there are
divergences in the fourth order (one loop) diagram. It is found that the
contribution of that order is finite (and vanishing) for the case of parallel
spin projections while the antiparallel case displays divergences which are
known to characterize the spin zero case in field theory as well as in quantum
mechanics.Comment: 14 pages LaTeX, including 2 figures using eps
Chiral Condensate in Holographic QCD with Baryon Density
We consider the chiral condensate in the baryonic dense medium using the
generalized Sakai-Sugimoto model. It is defined as the vacuum expectation value
of open Wilson line that is proposed to be calculated by use of the area of
world-sheet instanton. We evaluate it in confined as well as deconfined phase.
In both phases, the chiral condensate has a minimum as a function of baryon
density. In the deconfined phase, taking into account the chiral symmetry
restoration, we classify the behavior of chiral condensate into three types.
One can set the parameter of the theory such that the results, in low but
sufficiently higher density, is in agreement with the expectation from QCD.Comment: 23 pages, 8 figure
Boundary states in the Nappi-Witten model
We investigate D-branes in the Nappi-Witten model. Classically symmetric
D-branes are classified by the (twisted) conjugacy classes of the Nappi-Witten
group, which specify the geometry of the corresponding D-branes. Quantum
description of the D-branes is given by boundary states, and we need one point
functions of closed strings to construct the boundary states. We compute the
one point functions solving conformal bootstrap constraints, and check that the
classical limit of the boundary states reproduces the geometry of D-branes.Comment: 19 pages, no figure; minor changes, references adde
The Splitting of Branes on Orientifold Planes
Continuing the study in hep-th/0004092 and hep-th/0004092, we investigate a
non-trivial string dynamical process related to orientifold planes, i.e., the
splitting of physical NS-branes and D(p+2)-branes on orientifold Op-planes.
Creation or annihilation of physical Dp-branes usually accompanies the
splitting process. In the particular case p=4, we use Seiberg-Witten curves as
an independent method to check the results.Comment: 34 pages, 9 figure
- …