10,009 research outputs found
Running spectral index from shooting-star moduli
We construct an inflationary model that is consistent with both large
non-Gaussianity and a running spectral index. The scenario of modulated
inflation suggests that modulated perturbation can induce the curvature
perturbation with a large non-Gaussianity, even if the inflaton perturbation is
negligible. Using this idea, we consider a multi-field extension of the
modulated inflation scenario and examine the specific situation where different
moduli are responsible for the perturbation at different scales. We suppose
that the additional moduli (shooting-star moduli) is responsible for the
curvature perturbation at the earlier inflationary epoch and it generates the
fluctuation with n>1 spectral index at this scale. After a while, another
moduli (or inflaton) takes the place and generates the perturbation with n<1.
At the transition point the two fluctuations are comparable with each other. We
show how the spectral index is affected by the transition induced by the
shooting-star moduli.Comment: 14 pages, latex, accepted for publication in JHE
Remote Inflation: Hybrid-like inflation without hybrid-type potential
A new scenario of hybrid-like inflation is considered without using
hybrid-type potential. Radiation raised continuously by a dissipating inflaton
field keeps symmetry restoration in a remote sector, and the false-vacuum
energy of the remote sector dominates the energy density during inflation.
Remote inflation is terminated when the temperature reaches the critical
temperature, or when the slow-roll condition is violated. Without introducing a
complex form of couplings, inflaton field may either roll-in (like a standard
hybrid inflation) or roll-out (like an inverted-hybrid model or quintessential
inflation) on arbitrary inflaton potential. Significant signatures of remote
inflation can be observed in the spectrum caused by (1) the inhomogeneous phase
transition in the remote sector, or (2) a successive phase transition in the
remote sector. Remote inflation can predict strong amplification or suppression
of small-scale perturbations without introducing multiple inflation. Since the
inflaton may have a run-away potential, it is also possible to identify the
inflaton with quintessence, without introducing additional mechanisms. Even if
the false-vacuum energy is not dominated by the remote sector, the phase
transition in the remote sector is possible during warm inflation, which may
cause significant amplification/suppression of the curvature perturbations.Comment: 28 pages, 1 figure, fixed references, accepted for publication in
JCA
Generating the curvature perturbation with instant preheating
A new mechanism for generating the curvature perturbation at the end of
inflaton has been investigated. The dominant contribution to the primordial
curvature perturbation may be generated during the period of instant
preheating. The mechanism converts isocurvature perturbation related to a light
field into curvature perturbation, where the ``light field'' is not the
inflaton field. This mechanism is important in inflationary models where
kinetic energy is significant at the end of inflaton. We show how one can apply
this mechanism to various brane inflationary models.Comment: 17 pages, 1 figure, To appear in JCA
Brane inflation without slow-roll
The scenario of brane inflation without using the conventional slow-roll
approximations has been investigated. Based on the mechanism of generating the
curvature perturbations at the end of inflation, a new brane inflation paradigm
was developed. The conditions for making a sufficiently large enough number of
e-foldings and for generating the curvature perturbations without producing
dangerous relics were also examined. Benefits of our scenario are subsequently
discussed in detail.Comment: 21 pages, 2 figures, added an appendix, accepted for publication in
JHE
Evolution of the curvature perturbations during warm inflation
This paper considers warm inflation as an interesting application of
multi-field inflation. Delta-N formalism is used for the calculation of the
evolution of the curvature perturbations during warm inflation. Although the
perturbations considered in this paper are decaying after the horizon exit, the
corrections to the curvature perturbations sourced by these perturbations can
remain and dominate the curvature perturbations at large scales. In addition to
the typical evolution of the curvature perturbations, inhomogeneous diffusion
rate is considered for warm inflation, which may lead to significant
non-Gaussianity of the spectrum.Comment: 23 pages, 1 figure, fixed references, accepted for publication in
JCA
String production after angled brane inflation
We describe string production after angled brane inflation. First, we point
out that there was a discrepancy in previous discussions. The expected tension
of the cosmic string calculated from the four-dimensional effective Lagrangian
did not match the one obtained in the brane analysis. In the previous analysis,
the cosmic string is assumed to correspond to the lower-dimensional daughter
brane, which wraps the same compactified space as the original mother brane. In
this case, however, the tension of the daughter brane cannot depend on the
angle (\theta). On the other hand, from the analysis of the effective
Lagrangian for tachyon condensation, it is easy to see that the tension of the
cosmic string must be proportional to \theta, when \theta << 1. This is an
obvious discrepancy that must be explained by consideration of the explicit
brane dynamics. In this paper, we will solve this problem by introducing a
simple idea. We calculate the tension of the string in the two cases, which
matches precisely. The cosmological constraint for angled inflation is relaxed,
because the expected tension of the cosmic string becomes smaller than the one
obtained in previous arguments, by a factor of \theta.Comment: 13pages, 3 figures, typos correcte
Q ball inflation
We show that inflation can occur in the core of a Q-ball.Comment: 11 pages, latex2e, no figure, references added, final version to
appear in PR
Magnetic ordering of weakly coupled frustrated quantum spin chains
The ordering temperature of a quasi-one-dimensional system, consisting of
weakly interacting quantum spin-1/2 chains with antiferromagnetic
spin-frustrating couplings (or zig-zag ladder) is calculated. The results show
that a quantum critical point between two phases of the one-dimensional
subsystem plays a crucial role. If the one-dimensional subsystem is in the
antiferromagnetic-like phase in the ground state, similar to the phase of a
spin chain without frustration, weak couplings yield magnetic ordering of the
Neel type. For intra-chain spin-frustrating interactions larger than the
critical one (at which the quantum phase transition takes place), the
quasi-one-dimensional spin system manifests a spiral magnetic incommensurate
ordering. The obtained results of our quantum theory are compared with the
quasi-classical approximations. The calculated features of magnetic ordering
are expected to be generic for weakly coupled quantum spin chains with gapless
excitations and spin-frustrating nearest and next-nearest neighbor
interactions.Comment: 6 pages, 2 figure
Formation of monopoles and domain walls after brane inflation
We study cosmological defect formation after brane inflation. The
cosmological defects are corresponding to the branes that have less than three
spacial dimensions in the uncompactified spacetime. Contrary to the previous
arguments, production of monopoles and domain walls are not always negligible.
Monopoles and domain walls are formed by the branes extended between mother
branes.Comment: 27pages, 7 figures, many comments, footnotes and reviews are added,
to appear in JHE
Doping evolution of the electronic specific heat coefficient in slightly-doped La2-xSrxCuO4 single crystals
Detailed doping dependence of the electronic specific heat coefficient gamma
is studied for La2-xSrxCuO4 (LSCO) single crystals in the slightly-doped
regime. We find that gamma systematically increases with doping, and
furthermore, even for the samples in the antiferromagnetic (AF) regime, gamma
already acquires finite value and grows with x. This suggests that finite
electronic density of states (DOS) is created in the AF regime where the
transport shows strong localization at low temperatures, and this means the
system is not a real insulator with a clear gap even though it still keeps long
range AF order.Comment: 4 pages, 4 figures, accepted for publication in Journal of Physics:
Conference Series (LT25 proceeding
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