104,543 research outputs found
The Strong Multifield Slowroll Condition and Spiral Inflation
We point out the existing confusions about the slowroll parameters and
conditions for multifield inflation. If one requires the fields to roll down
the gradient flow, we find that only articles adopting the Hubble slowroll
expansion are on the right track, and a correct condition can be found in a
recent book by Liddle and Lyth. We further analyze this condition and show that
the gradient flow requirement is stronger than just asking for a slowly
changing, quasi-de Sitter solution. Therefore it is possible to have a
multifield slowroll model that does not follow the gradient flow. Consequently,
it no longer requires the gradient to be small. It even bypasses the first
slowroll condition and some related no-go theorems from string theory. We
provide the "spiral inflation" as a generic blueprint of such inflation model
and show that it relies on a monodromy locus---a common structure in string
theory effective potentials.Comment: 12 pages, version 4, cosmetic changes recommended by referee,
resubmitting to PR
Probability of Slowroll Inflation in the Multiverse
Slowroll after tunneling is a crucial step in one popular framework of the
multiverse---false vacuum eternal inflation (FVEI). In a landscape with a large
number of fields, we provide a heuristic estimation for its probability. We
find that the chance to slowroll is exponentially suppressed, where the
exponent comes from the number of fields. However, the relative probability to
have more e-foldings is only mildly suppressed as with
. Base on these two properties, we show that the FVEI picture is
still self-consistent and may have a strong preference between different
slowroll models.Comment: version 3, 21 pages, resubmit to PRD recommanded by refere
Recent results from BRAHMS
The BRAHMS collaboration ended its data collection program in 2006. We are
now well advanced in the analysis of a comprehensive set of data that spans
systems ranging in mass from p+p to Au+Au and in energy from to 200 GeV. Our analysis has taken two distinct paths: we explore the
rapidity dependence of intermediate and high-transverse-momentum,
identified-particle production, thus helping to characterize the
strongly-interacting quark-gluon plasma (sQGP) formed at RHIC; we also explore
particle yields at lower transverse momentum to develop a systematic
understanding of bulk particle production at RHIC energies.Comment: 8 pages, 5 figures, presented at the 20th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions, "Quark Matter 2008", Jaipur,
India, February 4-10, 200
The Energy of the Gamma Metric in the M{\o}ller Prescription
We obtain the energy distribution of the gamma metric using the
energy-momentum complex of M{\o}ller. The result is the same as obtained by
Virbhadra in the Weinberg prescription
Photodetachment of H near a partial reflecting surface
Theoretical and interpretative study on the subject of photodetachment of
H near a partial reflecting surface is presented, and the absorption
effect of the surface is investigated on the total and differential cross
sections using a theoretical imaging method. To understand the absorption
effect, a reflection parameter is introduced as a multiplicative factor to
the outgoing detached-electron wave of H propagating toward the wall. The
reflection parameter measures, how much electron wave would reflect from the
surface; K=0 corresponds to no reflection and K=1 corresponds to the total
reflection.Comment: 8 pages, 4 figure
The nonperturbative closed string tachyon vacuum to high level
We compute the action of closed bosonic string field theory at quartic order
with fields up to level ten. After level four, the value of the potential at
the minimum starts oscillating around a nonzero negative value, in contrast
with the proposition made in [5]. We try a different truncation scheme in which
the value of the potential converges faster with the level. By extrapolating
these values, we are able to give a rather precise value for the depth of the
potential.Comment: 24 pages. v2: typos corrected, clarified extrapolation in scheme B,
and added extrapolated tachyon and dilaton vev's at the end of Section
Higher-order vortex solitons, multipoles, and supervortices on a square optical lattice
We predict new generic types of vorticity-carrying soliton complexes in a
class of physical systems including an attractive Bose-Einstein condensate in a
square optical lattice (OL) and photonic lattices in photorefractive media. The
patterns include ring-shaped higher-order vortex solitons and supervortices.
Stability diagrams for these patterns, based on direct simulations, are
presented. The vortex ring solitons are stable if the phase difference \Delta
\phi between adjacent solitons in the ring is larger than \pi/2, while the
supervortices are stable in the opposite case, \Delta \phi <\pi /2. A
qualitative explanation to the stability is given.Comment: 9 pages, 4 figure
Modifying the photodetachment near a metal surface by a weak electric field
We show the photodetachment cross sections of H near a metal surface can be
modified using a weak static electric field. The modification is possible
because the oscillatory part of the cross section near a metal surface is
directly connected with the transit-time and the action of the
detached-electron closed-orbit which can be changed systematically by varying
the static electric field strength. Photodetachment cross sections for various
photon energies and electric field values are calculated and displayed.Comment: 16 pages, 7 figure
A two-dimensional numerical study of the flow inside the combustion chambers of a motored rotary engine
A numerical study was performed to investigate the unsteady, multidimensional flow inside the combustion chambers of an idealized, two-dimensional, rotary engine under motored conditions. The numerical study was based on the time-dependent, two-dimensional, density-weighted, ensemble-averaged conservation equations of mass, species, momentum, and total energy valid for two-component ideal gas mixtures. The ensemble-averaged conservation equations were closed by a K-epsilon model of turbulence. This K-epsilon model of turbulence was modified to account for some of the effects of compressibility, streamline curvature, low-Reynolds number, and preferential stress dissipation. Numerical solutions to the conservation equations were obtained by the highly efficient implicit-factored method of Beam and Warming. The grid system needed to obtain solutions were generated by an algebraic grid generation technique based on transfinite interpolation. Results of the numerical study are presented in graphical form illustrating the flow patterns during intake, compression, gaseous fuel injection, expansion, and exhaust
Vortex Lattice Structure of Fulde-Ferrell-Larkin-Ovchinnikov Superconductors
In superconductors with singlet pairing, the inhomogeneous
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state is expected to be stabilized by a
large Zeeman splitting. We develop an efficient method to evaluate the
Landau-Ginzburg free energies of FFLO-state vortex lattices and use it to
simplify the considerations that determine the optimal vortex configuration at
different points in the phasediagram. We demonstrate that the order parameter
spatial profile is completely determined, up to a uniform translation, by its
Landau level index n and the vortex Lattice structure and derive an explicit
expression for the order parameter spatial profile that can be used to
determine n from experimental data.Comment: 6 pages with one embedded color figure. Minor changes. Final version
as publishe
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