1,358 research outputs found
Standard-smooth hybrid inflation
We consider the extended supersymmetric Pati-Salam model which, for mu>0 and
universal boundary conditions, succeeds to yield experimentally acceptable
b-quark masses by moderately violating Yukawa unification. It is known that
this model can lead to new shifted or new smooth hybrid inflation. We show that
a successful two-stage inflationary scenario can be realized within this model
based only on renormalizable superpotential interactions. The cosmological
scales exit the horizon during the first stage of inflation, which is of the
standard hybrid type and takes place along the trivial flat direction with the
inflaton driven by radiative corrections. Spectral indices compatible with the
recent data can be achieved in global supersymmetry or minimal supergravity by
restricting the number of e-foldings of our present horizon during the first
inflationary stage. The additional e-foldings needed for solving the horizon
and flatness problems are naturally provided by a second stage of inflation,
which occurs mainly along the built-in new smooth hybrid inflationary path
appearing right after the destabilization of the trivial flat direction at its
critical point. Monopoles are formed at the end of the first stage of inflation
and are, subsequently, diluted by the second stage of inflation to become
utterly negligible in the present universe for almost all (for all) the allowed
values of the parameters in the case of global supersymmetry (minimal
supergravity).Comment: 11 pages including 2 figures, uses Revtex, version to appear in Phys.
Rev.
Initial Conditions for Supersymmetric Inflation
We perform a numerical investigation of the fields evolution in the
supersymmetric inflationary model based on radiative corrections. Supergravity
corrections are also included. We find that, out of all the examined initial
data, only about 10% give an adequate amount of inflation and can be considered
as ''natural''. Moreover, these successful initial conditions appear scattered
and more or less isolated.Comment: 15 pages RevTeX 4 eps figure
Chaoticity without thermalisation in disordered lattices
We study chaoticity and thermalization in Bose-Einstein condensates in
disordered lattices, described by the discrete nonlinear Schr\"odinger equation
(DNLS). A symplectic integration method allows us to accurately obtain both the
full phase space trajectories and their maximum Lyapunov exponents (mLEs),
which characterize their chaoticity. We find that disorder destroys ergodicity
by breaking up phase space into subsystems that are effectively disjoint on
experimentally relevant timescales, even though energetically, classical
localisation cannot occur. This leads us to conclude that the mLE is a very
poor ergodicity indicator, since it is not sensitive to the trajectory being
confined to a subregion of phase space. The eventual thermalization of a BEC in
a disordered lattice cannot be predicted based only on the chaoticity of its
phase space trajectory
Supersolid phases of dipolar bosons in optical lattices with a staggered flux
We present the theoretical mean-field zero-temperature phase diagram of a
Bose-Einstein condensate (BEC) with dipolar interactions loaded into an optical
lattice with a staggered flux. Apart from uniform superfluid, checkerboard
supersolid and striped supersolid phases, we identify several supersolid phases
with staggered vortices, which can be seen as combinations of supersolid phases
found in earlier work on dipolar BECs and a staggered-vortex phase found for
bosons in optical lattices with staggered flux. By allowing for different
phases and densities on each of the four sites of the elementary plaquette,
more complex phase patterns are found.Comment: 11 pages; added references, minor changes in tex
Extreme Events in Nonlinear Lattices
The spatiotemporal complexity induced by perturbed initial excitations
through the development of modulational instability in nonlinear lattices with
or without disorder, may lead to the formation of very high amplitude,
localized transient structures that can be named as extreme events. We analyze
the statistics of the appearance of these collective events in two different
universal lattice models; a one-dimensional nonlinear model that interpolates
between the integrable Ablowitz-Ladik (AL) equation and the nonintegrable
discrete nonlinear Schr\"odinger (DNLS) equation, and a two-dimensional
disordered DNLS equation. In both cases, extreme events arise in the form of
discrete rogue waves as a result of nonlinear interaction and rapid coalescence
between mobile discrete breathers. In the former model, we find power-law
dependence of the wave amplitude distribution and significant probability for
the appearance of extreme events close to the integrable limit. In the latter
model, more importantly, we find a transition in the the return time
probability of extreme events from exponential to power-law regime. Weak
nonlinearity and moderate levels of disorder, corresponding to weak chaos
regime, favour the appearance of extreme events in that case.Comment: Invited Chapter in a Special Volume, World Scientific. 19 pages, 9
figure
Nonlinear magnetoinductive transmission lines
Power transmission in one-dimensional nonlinear magnetic metamaterials driven
at one end is investigated numerically and analytically in a wide frequency
range. The nonlinear magnetic metamaterials are composed of varactor-loaded
split-ring resonators which are coupled magnetically through their mutual
inductances, forming thus a magnetoiductive transmission line. In the linear
limit, significant power transmission along the array only appears for
frequencies inside the linear magnetoinductive wave band. We present
analytical, closed form solutions for the magnetoinductive waves transmitting
the power in this regime, and their discrete frequency dispersion. When
nonlinearity is important, more frequency bands with significant power
transmission along the array may appear. In the equivalent circuit picture, the
nonlinear magnetoiductive transmission line driven at one end by a relatively
weak electromotive force, can be modeled by coupled
resistive-inductive-capacitive (RLC) circuits with voltage-dependent
capacitance. Extended numerical simulations reveal that power transmission
along the array is also possible in other than the linear frequency bands,
which are located close to the nonlinear resonances of a single nonlinear RLC
circuit. Moreover, the effectiveness of power transmission for driving
frequencies in the nonlinear bands is comparable to that in the linear band.
Power transmission in the nonlinear bands occurs through the linear modes of
the system, and it is closely related to the instability of a mode that is
localized at the driven site.Comment: 11 pages, 11 figures, submitted to International Journal of
Bifurcation and Chao
Simulation analysis of FDDI network using NETWORK II.5 software package
In recent years, one of the most exciting advances in media has been the use of fiber optics in LANs. The bandwidth provided by Fiber Optic Technology has drastically increased the number of new applications that can be supported by communication networks. In order to support a variety of services, in 1986, the American National Standard Institute (ANSI) Accredited Standards Committee (ASC) X3, and the ASC X3T9.5 Task Group developed a new standard; the Fiber Distributed Data Interface (FDDI) [1]. This is a high speed (100 Mbps) optical communication network based on a token passing mode of operation. The Medium Access Control (MAC) Protocol selected for this network attempts to provide priority services, as well as bounded delay transmission for real time applications [2].
This thesis presents results for the Voice-Data performance of the Medium Access Control (MAC) protocol, selected for the FDDI network, using the NETWORK 11.5 [6] software package. This protocol can provide priority services to different types of traffic, as well as guarantee bounded delays for real-time applications. The effect of various system parameters on performance is investigated
Leptogenesis through direct inflaton decay to light particles
We present a scenario of nonthermal leptogenesis following supersymmetric
hybrid inflation, in the case where inflaton decay to both heavy right handed
neutrino and SU(2)_L triplet superfields is kinematically disallowed. Lepton
asymmetry is generated through the decay of the inflaton into light particles
by the interference of one-loop diagrams with right handed neutrino and SU(2)_L
triplet exchange respectively. We require superpotential couplings explicitly
violating a U(1) R-symmetry and R-parity. However, the broken R-parity need not
have currently observable low-energy signatures. Also, the lightest sparticle
can be stable. Some R-parity violating slepton decays may, though, be
detectable in the future colliders. We take into account the constraints from
neutrino masses and mixing and the preservation of the primordial lepton
asymmetry.Comment: 11 pages including 3 figures, uses Revtex, minor corrections,
references adde
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