179 research outputs found
Heat kernel, effective action and anomalies in noncommutative theories
Being motivated by physical applications (as the phi^4 model) we calculate
the heat kernel coefficients for generalised Laplacians on the Moyal plane
containing both left and right multiplications. We found both star-local and
star-nonlocal terms. By using these results we calculate the large mass and
strong noncommutativity expansion of the effective action and of the vacuum
energy. We also study the axial anomaly in the models with gauge fields acting
on fermions from the left and from the right.Comment: 21 pages, v2: references adde
Moduli Space Dimensions of Multi-Pronged Strings
The numbers of bosonic and fermionic zero modes of multi-pronged strings are
counted in super-Yang-Mills theory and compared with those of the
IIB string theory. We obtain a nice agreement for the fermionic zero modes,
while our result for the bosonic zero modes differs from that obtained in the
IIB string theory. The possible origin of the discrepancy is discussedComment: 15 pages, 2 figure
Zero-Mode Dynamics of String Webs
At sufficiently low energy the dynamics of a string web is dominated by zero
modes involving rigid motion of the internal strings. The dimension of the
associated moduli space equals the maximal number of internal faces in the web.
The generic web moduli space has boundaries and multiple branches, and for webs
with three or more faces the geometry is curved. Webs can also be studied in a
lift to M-theory, where a string web is replaced by a membrane wrapped on a
holomorphic curve in spacetime. In this case the moduli space is complexified
and admits a Kaehler metric.Comment: LaTeX, 17 pages, 5 eps figures; v2: references adde
A Cooper pair light emitting diode
We demonstrate Cooper-pair's drastic enhancement effect on band-to-band
radiative recombination in a semiconductor. Electron Cooper pairs injected from
a superconducting electrode into an active layer by the proximity effect
recombine with holes injected from a p-type electrode and dramatically
accelerate the photon generation rates of a light emitting diode in the
optical-fiber communication band. Cooper pairs are the condensation of
electrons at a spin-singlet quantum state and this condensation leads to the
observed enhancement of the electric-dipole transitions. Our results indicate
the possibility to open up new interdisciplinary fields between
superconductivity and optoelectronics.Comment: 5 pages (4 figures
Analytic continuations of de Sitter thick domain wall solutions
We perform some analytic continuations of the de Sitter thick domain wall
solutions obtained in our previous paper hep-th/0201130 in the system of
gravity and a scalar field with an axion-like potential. The obtained new
solutions represent anti-de Sitter thick domain walls and cosmology. The
anti-de Sitter domain wall solutions are periodic, and correspondingly the
cosmological solutions represent cyclic universes. We parameterize the
axion-like scalar field potential and determine the parameter regions of each
type of solutions.Comment: Additons in section 5, 8 pages, 7 figures, RevTe
Strings from position-dependent noncommutativity
We introduce a new set of noncommutative space-time commutation relations in
two space dimensions. The space-space commutation relations are deformations of
the standard flat noncommutative space-time relations taken here to have
position dependent structure constants. Some of the new variables are
non-Hermitian in the most natural choice. We construct their Hermitian
counterparts by means of a Dyson map, which also serves to introduce a new
metric operator. We propose PTlike symmetries, i.e.antilinear involutory maps,
respected by these deformations. We compute minimal lengths and momenta arising
in this space from generalized versions of Heisenberg's uncertainty relations
and find that any object in this two dimensional space is string like,
i.e.having a fundamental length in one direction beyond which a resolution is
impossible. Subsequently we formulate and partly solve some simple models in
these new variables, the free particle, its PT-symmetric deformations and the
harmonic oscillator.Comment: 11 pages, Late
Thick de Sitter 3-Branes, Dynamic Black Holes and Localization of Gravity
The embedding of a thick de Sitter 3-brane into a five-dimensional bulk is
studied, assuming a scalar field with potential is present in the bulk. A class
of solutions is found in closed form that can represent a thick de Sitter
3-brane interpolating either between two dynamical black holes with a topology or between two Rindler-like spacetimes with a topology. The gravitational field is localized in a small region near
the center of the 3-brane. The analysis of graviton fluctuations shows that a
zero mode exists and separates itself from a set of continuous modes by a mass
gap. The existence of such a mass gap is shown to be universal. The scalar
perturbations are also studied and shown to be stable.Comment: the study of scalar perturbations and some relevant references have
been added. The most used definition for mass in de Sitter space has been
adopte
Fluctuation Induced Non-Fermi Liquid Behavior near a Quantum Phase Transition in Itinerant Electron Systems
The signature for a non-Fermi liquid behavior near a quantum phase transition
has been observed in thermal and transport properties of many metallic systems
at low temperatures. In the present work we consider specific examples of
itinerant ferromagnet as well as antiferromagnet in the limit of vanishing
transition temperature. The temperature variation of spin susceptibility,
electrical resistivity, specific heat, and NMR relaxation rates at low
temperatures is calculated in the limit of infinite exchange enhancement within
the frame work of a self consistent spin fluctuation theory. The resulting
non-Fermi liquid behavior is due to the presence of the low lying critically
damped spin fluctuations in these systems. The theory presented here gives the
leading low temperature behavior, as it turns out that the fluctuation
correlation term is always smaller than the mean fluctuation field term in
three as well as in two space dimensions. A comparison with illustrative
experimental results of these properties in some typical systems has been done.
Finally we make some remarks on the effect of disorder in these systems.Comment: File RevTex, 7 Figures available on request, Abstract and text
modified, To appear in Phys. Rev.
The accelerated scaling attractor solution of the interacting agegraphic dark energy in Brans-Dicke theory
We investigate the interacting agegraphic dark energy in Brans-Dicke theory
and introduce a new series general forms of dark sector coupling. As examples,
we select three cases involving a linear interaction form (Model I) and two
nonlinear interaction form (Model II and Model III). Our conclusions show that
the accelerated scaling attractor solutions do exist in these models. We also
find that these interacting agegraphic dark energy modes are consistent with
the observational data. The difference in these models is that nonlinear
interaction forms give more approached evolution to the standard CDM
model than the linear one. Our work implies that the nonlinear interaction
forms should be payed more attention.Comment: 9 pages, 10 figures, accepted in Eur. Phys. J.
Estimating Level of Engagement from Ocular Landmarks
E-learning offers many advantages like being economical, flexible and customizable, but also has challenging aspects such as lack of – social-interaction, which results in contemplation and sense of remoteness. To overcome these and sustain learners’ motivation, various stimuli can be incorporated. Nevertheless, such adjustments initially require an assessment of engagement level. In this respect, we propose estimating engagement level from facial landmarks exploiting the facts that (i) perceptual decoupling is promoted by blinking during mentally demanding tasks; (ii) eye strain increases blinking rate, which also scales with task disengagement; (iii) eye aspect ratio is in close connection with attentional state and (iv) users’ head position is correlated with their level of involvement. Building empirical models of these actions, we devise a probabilistic estimation framework. Our results indicate that high and low levels of engagement are identified with considerable accuracy, whereas medium levels are inherently more challenging, which is also confirmed by inter-rater agreement of expert coders
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