11,744 research outputs found
Molecular Hydrogen Emission from Protoplanetary Disks
We have modeled self-consistently the density and temperature profiles of gas
and dust in protoplanetary disks, taking into account irradiation from a
central star. Making use of this physical structure, we have calculated the
level populations of molecular hydrogen and the line emission from the disks.
As a result, we can reproduce the observed strong line spectra of molecular
hydrogen from protoplanetary disks, both in the ultraviolet (UV) and the
near-infrared, but only if the central star has a strong UV excess radiation.Comment: 19 pages, accepted for publication in Astronomy and Astrophysic
Localization-delocalization transition in one-dimensional electron systems with long-range correlated disorder
We investigate localization properties of electron eigenstates in
one-dimensional (1d) systems with long-range correlated diagonal disorder.
Numerical studies on the localization length of eigenstates demonstrate
the existence of the localization-delocalization transition in 1d systems and
elucidate non-trivial behavior of as a function of the disorder strength.
The critical exponent for localization length is extracted for various
values of parameters characterizing the disorder, revealing that every
disobeys the Harris criterion .Comment: 6 pages, 6 figuers, to be published in Phys. Rev.
Quantum Hall Ferromagnetism in Graphene
Graphene is a two-dimensional carbon material with a honeycomb lattice and
Dirac-like low-energy excitations. When Zeeman and spin-orbit interactions are
neglected its Landau levels are four-fold degenerate, explaining the
separation between quantized Hall conductivity values seen in recent
experiments. In this paper we derive a criterion for the occurrence of
interaction-driven quantum Hall effects near intermediate integer values of
due to charge gaps in broken symmetry states.Comment: 4 pages, 1 figur
Inflationary paradigm after Planck 2013
Models of cosmic inflation posit an early phase of accelerated expansion of
the universe, driven by the dynamics of one or more scalar fields in curved
spacetime. Though detailed assumptions about fields and couplings vary across
models, inflation makes specific, quantitative predictions for several
observable quantities, such as the flatness parameter ()
and the spectral tilt of primordial curvature perturbations (), among others---predictions that match the latest
observations from the {\it Planck} satellite to very good precision. In the
light of data from {\it Planck} as well as recent theoretical developments in
the study of eternal inflation and the multiverse, we address recent criticisms
of inflation by Ijjas, Steinhardt, and Loeb. We argue that their conclusions
rest on several problematic assumptions, and we conclude that cosmic inflation
is on a stronger footing than ever before.Comment: 11 pages, no figures; added references, and brief additions to
Footnote 1, Section VI, and the Acknowledgment
Renormalized Landau Levels and Particle-Hole Symmetry in Graphene
In this proceedings paper we report on a calculation of graphene's Landau
levels in a magnetic field. Our calculations are based on a self-consistent
Hartree-Fock approximation for graphene's massless-Dirac continuum model. We
find that because of graphene's chiral band structure interactions not only
shift Landau-level energies, as in a non-relativistic electron gas, but also
alter Landau level wavefunctions. We comment on the subtle continuum model
regularization procedure necessary to correctly maintain the lattice-model's
particle hole symmetry properties
Stable skyrmions from extra dimensions
We show that skyrmions arising from compact five dimensional models have
stable sizes. We numerically obtain the skyrmion configurations and calculate
their size and energy. Although their size strongly depends on the magnitude of
localized kinetic-terms, their energy is quite model-independent ranging
between 50-65 times F_pi^2/m_rho, where F_pi is the Goldstone decay constant
and m_rho the lowest Kaluza-Klein mass. These skyrmion configurations
interpolate between small 4D YM instantons and 4D skyrmions made of Goldstones
and a massive vector boson. Contrary to the original 4D skyrmion and previous
5D extensions, these configurations have sizes larger than the inverse of the
cut-off scale and therefore they are trustable within our effective 5D
approach. Such solitonic particles can have interesting phenomenological
consequences as they carry a conserved topological charge analogous to baryon
number.Comment: 20 pages, 3 figure
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