2,993 research outputs found
Geometrically Consistent Approach to Stochastic DBI Inflation
Stochastic effects during inflation can be addressed by averaging the quantum
inflaton field over Hubble-patch sized domains. The averaged field then obeys a
Langevin-type equation into which short-scale fluctuations enter as a noise
term. We solve the Langevin equation for a inflaton field with Dirac Born
Infeld (DBI) kinetic term perturbatively in the noise and use the result to
determine the field value's Probability Density Function (PDF). In this
calculation, both the shape of the potential and the warp factor are arbitrary
functions, and the PDF is obtained with and without volume effects due to the
finite size of the averaging domain. DBI kinetic terms typically arise in
string-inspired inflationary scenarios in which the scalar field is associated
with some distance within the (compact) extra dimensions. The inflaton's
accessible range of field values therefore is limited because of the extra
dimensions' finite size. We argue that in a consistent stochastic approach the
distance-inflaton's PDF must vanish for geometrically forbidden field values.
We propose to implement these extra-dimensional spatial restrictions into the
PDF by installing absorbing (or reflecting) walls at the respective boundaries
in field space. As a toy model, we consider a DBI inflaton between two
absorbing walls and use the method of images to determine its most general PDF.
The resulting PDF is studied in detail for the example of a quartic warp factor
and a chaotic inflaton potential. The presence of the walls is shown to affect
the inflaton trajectory for a given set of parameters.Comment: 20 pages, 3 figure
Tax research techniques;Studies in federal taxation, 5
https://egrove.olemiss.edu/aicpa_guides/1567/thumbnail.jp
Deconstructing (2,0) proposals
C. P. is supported by the U.S. Department of Energy under
Grant No. DE-FG02-96ER40959. M. S. S. is supported by
an EURYI award of the European Science Foundatio
Thermodynamic Entropy And The Accessible States of Some Simple Systems
Comparison of the thermodynamic entropy with Boltzmann's principle shows that
under conditions of constant volume the total number of arrangements in simple
thermodynamic systems with temperature-independent heat capacities is TC/k. A
physical interpretation of this function is given for three such systems; an
ideal monatomic gas, an ideal gas of diatomic molecules with rotational motion,
and a solid in the Dulong-Petit limit of high temperature. T1/2 emerges as a
natural measure of the number of accessible states for a single particle in one
dimension. Extension to N particles in three dimensions leads to TC/k as the
total number of possible arrangements or microstates. The different microstates
of the system are thus shown a posteriori to be equally probable, with
probability T-C/k, which implies that for the purposes of counting states the
particles of the gas are distinguishable. The most probable energy state of the
system is determined by the degeneracy of the microstates.Comment: 9 pages, 1 figur
Sommerfeld's image method in the calculation of van der Waals forces
We show how the image method can be used together with a recent method
developed by C. Eberlein and R. Zietal to obtain the dispersive van der Waals
interaction between an atom and a perfectly conducting surface of arbitrary
shape. We discuss in detail the case of an atom and a semi- infinite conducting
plane. In order to employ the above procedure to this problem it is necessary
to use the ingenious image method introduced by Sommerfeld more than one
century ago, which is a generalization of the standard procedure. Finally, we
briefly discuss other interesting situations that can also be treated by the
joint use of Sommerfeld's image technique and Eberlein-Zietal method.Comment: To appear in the proceedings of Conference on Quantum Field Theory
under the Influence of External Conditions (QFEXT11
Approximate Analytic Solution for the Spatiotemporal Evolution of Wave Packets undergoing Arbitrary Dispersion
We apply expansion methods to obtain an approximate expression in terms of
elementary functions for the space and time dependence of wave packets in a
dispersive medium. The specific application to pulses in a cold plasma is
considered in detail, and the explicit analytic formula that results is
provided. When certain general initial conditions are satisfied, these
expressions describe the packet evolution quite well. We conclude by employing
the method to exhibit aspects of dispersive pulse propagation in a cold plasma,
and suggest how predicted and experimental effects may be compared to improve
the theoretical description of a medium's dispersive properties.Comment: 17 pages, 4 figures, RevTe
Some Remarks about Variable Mass Systems
We comment about the general argument given to obtain the rocket equation as
it is exposed in standard textbooks. In our opinion, it can induce students to
a wrong answer when solving variable mass problems.Comment: 2 page
Transient terahertz spectroscopy of excitons and unbound carriers in quasi two-dimensional electron-hole gases
We report a comprehensive experimental study and detailed model analysis of
the terahertz dielectric response and density kinetics of excitons and unbound
electron-hole pairs in GaAs quantum wells. A compact expression is given, in
absolute units, for the complex-valued terahertz dielectric function of
intra-excitonic transitions between the 1s and higher-energy exciton and
continuum levels. It closely describes the terahertz spectra of resonantly
generated excitons. Exciton ionization and formation are further explored,
where the terahertz response exhibits both intra-excitonic and Drude features.
Utilizing a two-component dielectric function, we derive the underlying exciton
and unbound pair densities. In the ionized state, excellent agreement is found
with the Saha thermodynamic equilibrium, which provides experimental
verification of the two-component analysis and density scaling. During exciton
formation, in turn, the pair kinetics is quantitatively described by a Saha
equilibrium that follows the carrier cooling dynamics. The terahertz-derived
kinetics is, moreover, consistent with time-resolved luminescence measured for
comparison. Our study establishes a basis for tracking pair densities via
transient terahertz spectroscopy of photoexcited quasi-two-dimensional
electron-hole gases.Comment: 14 pages, 8 figures, final versio
Tax research techniques
https://egrove.olemiss.edu/aicpa_guides/1565/thumbnail.jp
Tax research techniques
https://egrove.olemiss.edu/aicpa_guides/1566/thumbnail.jp
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