3,429 research outputs found
Contact Terms and Duality Symmetry in The Critical Dissipative Hofstadter Model
The dissipative Hofstadter model describes the quantum mechanics of a charged
particle in two dimensions subject to a periodic potential, uniform magnetic
field, and dissipative force. Its phase diagram exhibits an SL(2,Z) duality
symmetry and has an infinite number of critical circles in the
dissipation/magnetic field plane. In addition, multi-critical points on a
particular critical circle correspond to non-trivial solutions of open string
theory. The duality symmetry is expected to provide relations between
correlation functions at different multi-critical points. Many of these
correlators are contact terms. However we expect them to have physical
significance because under duality they transform into functions that are
non-zero for large separations of the operators. Motivated by the search for
exact, regulator independent solutions for these contact terms, in this paper
we derive many properties and symmetries of the coordinate correlation
functions at the special multi-critical points. In particular, we prove that
the correlation functions are homogeneous, piecewise-linear functions of the
momenta, and we prove a weaker version of the anticipated duality
transformation. Consequently, the possible forms of the correlation functions
are limited to lie in a finite dimensional linear space. We treat the potential
perturbatively and these results are valid to all orders in perturbation
theory.Comment: 65 pages, six figures, CTP#217
Canonically quantized soliton in the bound state approach to heavy baryons in the Skyrme model
The bound state extension of Skyrme's topological soliton model for the heavy
baryons is quantized canonically in arbitrary reducible representations of the
SU(3) flavor group. The canonical quantization leads to an additional negative
mass term, which stabilizes the quantized soliton solution. The heavy flavor
meson in the field of the soliton is treated with semiclassical quantization.
The representation dependence of the calculated spectra for the strange, charm
and bottom baryons is explored and compared to the extant empirical spectra.Comment: 13 pages, 8 table
2D Dilaton-Maxwell Gravity as a Fixed Point of the Renormalization Group
A general model of dialton-Maxwell gravity in two dimensions is investigated.
The corresponding one-loop effective action and the generalized
-functions are obtained. A set of models that are fixed points of the
renormalization group equations are presented.Comment: 7 pages, LaTeX file, UB-ECM-PF 92/Mar1
Critical Theories of the Dissipative Hofstadter Model
It has recently been shown that the dissipative Hofstadter model (dissipative
quantum mechanics of an electron subject to uniform magnetic field and periodic
potential in two dimensions) exhibits critical behavior on a network of lines
in the dissipation/magnetic field plane. Apart from their obvious condensed
matter interest, the corresponding critical theories represent non-trivial
solutions of open string field theory, and a detailed account of their
properties would be interesting from several points of view. A subject of
particular interest is the dependence of physical quantities on the magnetic
field since it, much like , serves only to give relative
phases to different sectors of the partition sum. In this paper we report the
results of an initial investigation of the free energy, -point functions and
boundary state of this type of critical theory. Although our primary goal is
the study of the magnetic field dependence of these quantities, we will present
some new results which bear on the zero magnetic field case as well.Comment: 42 pages (25 reduced
Loop Variables and Gauge Invariance in (Open) Bosonic String Theory
We give a simplified and more complete description of the loop variable
approach for writing down gauge invariant equations of motion for the fields of
the open string. A simple proof of gauge invariance to all orders is given. In
terms of loop variables, the interacting equations look exactly like the free
equations, but with a loop variable depending on an extra parameter, thus
making it a band of finite width. The arguments for gauge invariance work
exactly as in the free case. We show that these equations are Wilsonian RG
equations with a finite world-sheet cutoff and that in the infrared limit,
equivalence with the Callan-Symanzik -functions should ensure that they
reproduce the on-shell scattering amplitudes in string theory. It is applied to
the tachyon-photon system and the general arguments for gauge invariance can be
easily checked to the order calculated. One can see that when there is a finite
world sheet cutoff in place, even the U(1) invariance of the equations for the
photon, involves massive mode contributions. A field redefinition involving the
tachyon is required to get the gauge transformations of the photon into
standard form.Comment: 20 pages, Late
Heavy quark potential in the instanton liquid model
We study the heavy quark potential in the instanton liquid model by carefully
measuring Wilson loops out to a distance of order 3. A random instanton
ensemble with a fixed radius = 1/3 generates a potential
growing very slowly at large . In contrast, a more realistic size
distribution growing as at small and decaying as at
large , leads to a potential which grows linearly with . The string
tension, however, is only about 1/10 of the phenomenological value.Comment: LATTICE98(confine
Multisensory Integration Sites Identified by Perception of Spatial Wavelet Filtered Visual Speech Gesture Information
Perception of speech is improved when presentation of the audio signal is accompanied by concordant visual speech gesture information. This enhancement is most prevalent when the audio signal is degraded. One potential means by which the brain affords perceptual enhancement is thought to be through the integration of concordant information from multiple sensory channels in a common site of convergence, multisensory integration (MSI) sites. Some studies have identified potential sites in the superior temporal gyrus/sulcus (STG/S) that are responsive to multisensory information from the auditory speech signal and visual speech movement. One limitation of these studies is that they do not control for activity resulting from attentional modulation cued by such things as visual information signaling the onsets and offsets of the acoustic speech signal, as well as activity resulting from MSI of properties of the auditory speech signal with aspects of gross visual motion that are not specific to place of articulation information. This fMRI experiment uses spatial wavelet bandpass filtered Japanese sentences presented with background multispeaker audio noise to discern brain activity reflecting MSI induced by auditory and visual correspondence of place of articulation information that controls for activity resulting from the above-mentioned factors. The experiment consists of a low-frequency (LF) filtered condition containing gross visual motion of the lips, jaw, and head without specific place of articulation information, a midfrequency (MF) filtered condition containing place of articulation information, and an unfiltered (UF) condition. Sites of MSI selectively induced by auditory and visual correspondence of place of articulation information were determined by the presence of activity for both the MF and UF conditions relative to the LF condition. Based on these criteria, sites of MSI were found predominantly in the left middle temporal gyrus (MTG), and the left STG/S (including the auditory cortex). By controlling for additional factors that could also induce greater activity resulting from visual motion information, this study identifies potential MSI sites that we believe are involved with improved speech perception intelligibility
Dirichlet Boundary State in Linear Dilaton Background
Dirichlet-branes have emerged as important objects in studying
nonperturbative string theory. It is important to generalize these objects to
more general backgrounds other than the usual flat background. The simplest
case is the linear dilaton condensate. The usual Dirichlet boundary condition
violates conformal invariance in such a background. We show that by switching
on a certain boundary interaction, conformal invariance is restored. An
immediate application of this result is to two dimensional string theory.Comment: 6 pages, harvmac, some remarks are modified and one reference is
added, formulas remain the sam
The More, the Not Marry-Er: In Search of a Policy Behind Eligibility for California Domestic Partnerships
This Comment examines California Assembly Bill 25 which grants certain civic rights to state-registered domestic partners. The author seeks to provide background to the development of the current statutory scheme and examine whether any coherent policy supports the statute\u27s expansion to include greater numbers of opposite-sex couples. The author begins by examining the substantive benefits that California domestic partnerships provide and to whom those benefits are offered. She continues to explore the background of the current domestic partnership scheme in California against the backdrop of the ways that other states have sought to address the needs of nontraditional couples and families. The author then examines the legislative history of Assembly Bill 25 and the possible purposes behind expanding eligibility for domestic partnerships. The author concludes that there is no concrete policy behind such an expansion. She offers suggestions regarding the likely purpose behind this expansion and recommends that other states that wish to follow California\u27s model adopt a clear policy behind eligibility
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