76,592 research outputs found
New line-interactive UPS system with DSP-based active power-line conditioning
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Quasiparticle Interference on the Surface of the Topological Insulator BiTe
The quasiparticle interference of the spectroscopic imaging scanning
tunneling microscopy has been investigated for the surface states of the large
gap topological insulator BiTe through the T-matrix formalism. Both the
scalar potential scattering and the spin-orbit scattering on the warped
hexagonal isoenergy contour are considered. While backscatterings are forbidden
by time-reversal symmetry, other scatterings are allowed and exhibit strong
dependence on the spin configurations of the eigenfunctions at k points over
the isoenergy contour. The characteristic scattering wavevectors found in our
analysis agree well with recent experiment results.Comment: 5 pages, 2 figures, Some typos are correcte
Quantization of a Friedmann-Robertson-Walker model in N=1 Supergravity with Gauged Supermatter
The theory of N = 1 supergravity with gauged supermatter is studied in the
context of a k = + 1 Friedmann minisuperspace model. It is found by imposing
the Lorentz and supersymmetry constraints that there are {\seveni no} physical
states in the particular SU(2) model studied.Comment: 5 pages, Talk at the 1st Mexican School in Gravitation and
mathematical physics, Guanajuato, Mexico, December 12-16 199
Direct CP violation in two-body hadronic charmed meson decays
Motivated by the recent observation of CP violation in the charm sector by
LHCb, we study direct CP asymmetries in the standard model (SM) for the singly
Cabibbo-suppressed two-body hadronic decays of charmed mesons using the
topological-diagram approach. In this approach, the magnitude and the phase of
topological weak annihilation amplitudes which arise mainly from final-state
rescattering can be extracted from the data. Consequently, direct CP asymmetry
at tree level can be reliably estimated. In general, it
lies in the range . Short-distance QCD
penguins and penguin annihilation are calculated using QCD factorization. Their
effects are generally small, especially for modes. Since weak penguin
annihilation receives long-distance contributions from the color-allowed tree
amplitude followed by final-state rescattering, it is expected to give the
dominant contribution to the direct CP violation in the decays
and in which is absent. The maximal
, the direct CP asymmetry difference between the
above-mentioned two modes, allowed in the SM is around -0.25%, more than
away from the current world average of .Comment: 19 pages, 2 figures; typos correcte
Probing the SUSY breaking scale at an collider
If supersymmetry is spontaneously at a low energy scale then the resulting
gravitino would be very light. The interaction strength of the longitudinal
components of such a light gravitino to electron-selectron pair then becomes
comparable to that of electroweak interactions. Such a light gravitino could
modify the cross-section for e^_L e^_R-->\tilde {e}_L\tilde {e}_R from its
MSSM value. Precision measurement of this cross-section could therefore be used
to probe the low energy SUSY breaking scale.Comment: Plain Tex, 7 pages, No figure
Exclusive Hadronic D Decays to eta' and eta
Hadronic decay modes and
are studied in the generalized
factorization approach. Form factors for transitions
are carefully evaluated by taking into account the wave function normalization
of the eta and eta'. The predicted branching ratios are generally in agreement
with experiment except for and
; the calculated decay rates for the first two decay modes
are too small by an order of magnitude. We show that the weak decays and followed by resonance-induced final-state
interactions (FSI), which are amenable technically, are able to enhance the
branching ratios of and dramatically
without affecting the agreement between theory and experiment for and . We argue that it is difficult to understand
the observed large decay rates of and
simultaneously; FSI, W-annihilation and the production of excess eta' from
gluons are not helpful in this regard. The large discrepancy between the
factorization hypothesis and experiment for the ratio of
and remains as an enigma.Comment: 15 pages, 1 figure, to appear in Phys. Rev. D. Form factors for D to
eta and eta' transitions are slightly change
Finite Temperature Casimir Effect and Dispersion in the Presence of Compactified Extra Dimensions
Finite temperature Casimir theory of the Dirichlet scalar field is developed,
assuming that there is a conventional Casimir setup in physical space with two
infinitely large plates separated by a gap R and in addition an arbitrary
number q of extra compacified dimensions. As a generalization of earlier
theory, we assume in the first part of the paper that there is a scalar
'refractive index' N filling the whole of the physical space region. After
presenting general expressions for free energy and Casimir forces we focus on
the low temperature case, as this is of main physical interest both for force
measurements and also for issues related to entropy and the Nernst theorem.
Thereafter, in the second part we analyze dispersive properties, assuming for
simplicity q=1, by taking into account dispersion associated with the first
Matsubara frequency only. The medium-induced contribution to the free energy,
and pressure, is calculated at low temperatures.Comment: 25 pages, one figure. Minor changes in the discussion. Version to
appear in Physica Script
Matching Stages of Heavy Ion Collision Models
Heavy ion reactions and other collective dynamical processes are frequently
described by different theoretical approaches for the different stages of the
process, like initial equilibration stage, intermediate locally equilibrated
fluid dynamical stage and final freeze-out stage. For the last stage the best
known is the Cooper-Frye description used to generate the phase space
distribution of emitted, non-interacting, particles from a fluid dynamical
expansion/explosion, assuming a final ideal gas distribution, or (less
frequently) an out of equilibrium distribution. In this work we do not want to
replace the Cooper-Frye description, rather clarify the ways how to use it and
how to choose the parameters of the distribution, eventually how to choose the
form of the phase space distribution used in the Cooper-Frye formula. Moreover,
the Cooper-Frye formula is used in connection with the freeze-out problem,
while the discussion of transition between different stages of the collision is
applicable to other transitions also. More recently hadronization and molecular
dynamics models are matched to the end of a fluid dynamical stage to describe
hadronization and freeze-out. The stages of the model description can be
matched to each other on spacetime hypersurfaces (just like through the
frequently used freeze-out hypersurface). This work presents a generalized
description of how to match the stages of the description of a reaction to each
other, extending the methodology used at freeze-out, in simple covariant form
which is easily applicable in its simplest version for most applications.Comment: 9 pages, 2 figure
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