988 research outputs found
Multi-field Inflation with a Random Potential
Motivated by the possibility of inflation in the cosmic landscape, which may
be approximated by a complicated potential, we study the density perturbations
in multi-field inflation with a random potential. The random potential causes
the inflaton to undergo a Brownian motion with a drift in the D-dimensional
field space. To quantify such an effect, we employ a stochastic approach to
evaluate the two-point and three-point functions of primordial perturbations.
We find that in the weakly random scenario the resulting power spectrum
resembles that of the single field slow-roll case, with up to 2% more red tilt.
The strongly random scenario, leads to rich phenomenologies, such as primordial
fluctuations in the power spectrum on all angular scales. Such features may
already be hiding in the error bars of observed CMB TT (as well as TE and EE)
power spectrum and can be detected or falsified with more data coming in the
future. The tensor power spectrum itself is free of fluctuations and the tensor
to scalar ratio is enhanced. In addition a large negative running of the power
spectral index is possible. Non-Gaussianity is generically suppressed by the
growth of adiabatic perturbations on super-horizon scales, but can possibly be
enhanced by resonant effects or arise from the entropic perturbations during
the onset of (p)reheating. The formalism developed in this paper can be applied
to a wide class of multi-field inflation models including, e.g. the N-flation
scenario.Comment: More clarifications and references adde
Multi-field Inflation with a Random Potential
Motivated by the possibility of inflation in the cosmic landscape, which may
be approximated by a complicated potential, we study the density perturbations
in multi-field inflation with a random potential. The random potential causes
the inflaton to undergo a Brownian motion with a drift in the D-dimensional
field space. To quantify such an effect, we employ a stochastic approach to
evaluate the two-point and three-point functions of primordial perturbations.
We find that in the weakly random scenario the resulting power spectrum
resembles that of the single field slow-roll case, with up to 2% more red tilt.
The strongly random scenario, leads to rich phenomenologies, such as primordial
fluctuations in the power spectrum on all angular scales. Such features may
already be hiding in the error bars of observed CMB TT (as well as TE and EE)
power spectrum and can be detected or falsified with more data coming in the
future. The tensor power spectrum itself is free of fluctuations and the tensor
to scalar ratio is enhanced. In addition a large negative running of the power
spectral index is possible. Non-Gaussianity is generically suppressed by the
growth of adiabatic perturbations on super-horizon scales, but can possibly be
enhanced by resonant effects or arise from the entropic perturbations during
the onset of (p)reheating. The formalism developed in this paper can be applied
to a wide class of multi-field inflation models including, e.g. the N-flation
scenario.Comment: More clarifications and references adde
Adding a Brane to the Brane-Anti-Brane Action in BSFT
We attempt to generalize the effective action for the D-brane-anti-D-brane
system obtained from boundary superstring field theory (BSFT) by adding an
extra D-brane to it to obtain a covariantized action for 2 D-branes and 1
anti-D-brane. We discuss the approximations made to obtain the effective action
in closed form. Among other properties, this effective action admits solitonic
solutions of codimension 2 (vortices) when one of the D-brane is far separated
from the brane-anti-brane pair.Comment: 23 pages, 2 figures, minor revision
A certain class of Laplace transforms with applications to reaction and reaction-diffusion equations
A class of Laplace transforms is examined to show that particular cases of
this class are associated with production-destruction and reaction-diffusion
problems in physics, study of differences of independently distributed random
variables and the concept of Laplacianness in statistics, alpha-Laplace and
Mittag-Leffler stochastic processes, the concepts of infinite divisibility and
geometric infinite divisibility problems in probability theory and certain
fractional integrals and fractional derivatives. A number of applications are
pointed out with special reference to solutions of fractional reaction and
reaction-diffusion equations and their generalizations.Comment: LaTeX, 12 pages, corrected typo
Reaction-diffusion systems and nonlinear waves
The authors investigate the solution of a nonlinear reaction-diffusion
equation connected with nonlinear waves. The equation discussed is more general
than the one discussed recently by Manne, Hurd, and Kenkre (2000). The results
are presented in a compact and elegant form in terms of Mittag-Leffler
functions and generalized Mittag-Leffler functions, which are suitable for
numerical computation. The importance of the derived results lies in the fact
that numerous results on fractional reaction, fractional diffusion, anomalous
diffusion problems, and fractional telegraph equations scattered in the
literature can be derived, as special cases, of the results investigated in
this article.Comment: LaTeX, 16 pages, corrected typo
Tunneling and propagation of vacuum bubbles on dynamical backgrounds
In the context of bubble universes produced by a first-order phase transition
with large nucleation rates compared to the inverse dynamical time scale of the
parent bubble, we extend the usual analysis to non-vacuum backgrounds. In
particular, we provide semi-analytic and numerical results for the modified
nucleation rate in FLRW backgrounds, as well as a parameter study of bubble
walls propagating into inhomogeneous (LTB) or FLRW spacetimes, both in the
thin-wall approximation. We show that in our model, matter in the background
often prevents bubbles from successful expansion and forces them to collapse.
For cases where they do expand, we give arguments why the effects on the
interior spacetime are small for a wide range of reasonable parameters and
discuss the limitations of the employed approximations.Comment: 29 pages, 8 figures, typos corrected, matches published versio
Spectral flow and boundary string field theory for angled D-branes
D-branes intersecting at an arbitrary fixed angle generically constitute a
configuration unstable toward recombination. The reconnection of the branes
nucleates at the intersection point and involves a generalization of the
process of brane decay of interest to non-perturbative string dynamics as well
as cosmology. After reviewing the string spectrum of systems of angled branes,
we show that worldsheet twist superfields may be used in the context of
Boundary Superstring Field Theory to describe the dynamics. Changing the angle
between the branes is seen from the worldsheet as spectral flow with boundary
insertions flowing from bosonic to fermionic operators. We calculate the
complete tachyon potential and the low energy effective action as a function of
angle and find an expression that interpolates between the brane-antibrane and
the Dirac-Born-Infeld actions. The potential captures the mechanism of D-brane
recombination and provides for interesting new physics for tachyon decay.Comment: 32 pages, 9 figures; v2 references added; v3 discussion clarifie
Solution of generalized fractional reaction-diffusion equations
This paper deals with the investigation of a closed form solution of a
generalized fractional reaction-diffusion equation. The solution of the
proposed problem is developed in a compact form in terms of the H-function by
the application of direct and inverse Laplace and Fourier transforms.
Fractional order moments and the asymptotic expansion of the solution are also
obtained.Comment: LaTeX, 18 pages, corrected typo
Re-Focusing - Building a Future for Entrepreneurial Education & Learning
The field of entrepreneurship has struggled with fundamental
questions concerning the subjectâs nature and purpose. To whom and to
what means are educational and training agendas ultimately directed?
Such questions have become of central importance to policy makers,
practitioners and academics alike. There are suggestions that university
business schools should engage more critically with the lived experiences
of practising entrepreneurs through alternative pedagogical approaches
and methods, seeking to account for and highlighting the social, political
and moral aspects of entrepreneurial practice. In the UK, where funding in
higher education has become increasingly dependent on student fees,
there are renewed pressures to educate students for entrepreneurial
practice as opposed to educating them about the nature and effects of
entrepreneurship. Government and EU policies are calling on business
schools to develop and enhance entrepreneurial growth and skill sets, to
make their education and training programmes more proactive in
providing innovative educational practices which help and facilitate life
experiences and experiential learning. This paper makes the case for
critical frameworks to be applied so that complex social processes
become a source of learning for educators and entrepreneurs and so that
innovative pedagogical approaches can be developed in terms both of
context (curriculum design) and process (delivery methods)
An Improved Brane Anti-Brane Action from Boundary Superstring Field Theory and Multi-Vortex Solutions
We present an improved effective action for the D-brane-anti-D-brane system
obtained from boundary superstring field theory. Although the action looks
highly non-trivial, it has simple explicit multi-vortex (i.e. codimension-2
multi-BPS D-brane) multi-anti-vortex solutions. The solutions have a curious
degeneracy corresponding to different ``magnetic'' fluxes at the core of each
vortex. We also generalize the brane anti-brane effective action that is
suitable for the study of the inflationary scenario and the production of
defects in the early universe. We show that when a brane and anti-brane are
distantly separated, although the system is classically stable it can decay via
quantum tunneling through the barrier.Comment: 24 pages, 1 figure, JHEP3.cls; v2: references added, tunneling rate
discussion expande
- âŠ