14,275 research outputs found
Inflation without Inflaton(s)
We propose a model for early universe cosmology without the need for
fundamental scalar fields. Cosmic acceleration and phenomenologically viable
reheating of the universe results from a series of energy transitions, where
during each transition vacuum energy is converted to thermal radiation. We show
that this `cascading universe' can lead to successful generation of adiabatic
density fluctuations and an observable gravity wave spectrum in some cases,
where in the simplest case it reproduces a spectrum similar to slow-roll models
of inflation. We also find the model provides a reasonable reheating
temperature after inflation ends. This type of model may also be relevant for
addressing the smallness of the vacuum energy today.Comment: 13 pages, 4 figures, published versio
Modal expansions and non-perturbative quantum field theory in Minkowski space
We introduce a spectral approach to non-perturbative field theory within the
periodic field formalism. As an example we calculate the real and imaginary
parts of the propagator in 1+1 dimensional phi^4 theory, identifying both
one-particle and multi-particle contributions. We discuss the computational
limits of existing diagonalization algorithms and suggest new quasi-sparse
eigenvector methods to handle very large Fock spaces and higher dimensional
field theories.Comment: new material added, 12 pages, 6 figure
RPA for Light-Front Hamiltonian Field Theory
A self-consistent random phase approximation (RPA) is proposed as an
effective Hamiltonian method in Light-Front Field Theory (LFFT). We apply the
general idea to the light-front massive Schwinger model to obtain a new bound
state equation and solve it numerically.Comment: A major revision in presentation, while the results essentially
unchanged. 2 figs. replaced, 1 fig. added, some parts of Sec. V moved to Sec.
IV, some wording changed, typos correcte
The Gravitational Demise of Cold Degenerate Stars
We consider the long term fate and evolution of cold degenerate stars under
the action of gravity alone. Although such stars cannot emit radiation through
the Hawking mechanism, the wave function of the star will contain a small
admixture of black hole states. These black hole states will emit radiation and
hence the star can lose its mass energy in the long term. We discuss the
allowed range of possible degenerate stellar evolution within this framework.Comment: LaTeX, 18 pages, one figure, accepted to Physical Review
Accelerating universe emergent from the landscape
We propose that the existence of the string landscape suggests the universe
can be in a quantum glass state, where an extremely large viscosity is
generated, and long distance dynamics slows down. At the same time, the short
distance dynamics is not altered due to the separation of time scales. This
scenario can help to understand some controversies in cosmology, for example
the natural existence of slow roll inflation and dark energy in the landscape,
the apparent smallness of the cosmological constant. We see also that moduli
stabilization is no longer necessary. We further identify the glass transition
point, where the viscosity diverges, as the location of the cosmic horizon. We
try to reconstruct the geometry of the accelerating universe from the structure
of the landscape, and find that the metric should have an infinite jump when
crossing the horizon. We predict that the static coordinate metric for dS space
breaks down outside the horizon.Comment: 20 pages, no figures, harvma
Conductivity, weak ferromagnetism and charge instability in single crystal
The temperature dependence of resistivity, magnetization and electron-spin
resonance of the single crystal were measured in temperature
range of . Magnetization hysteresis in applied magnetic field
up to 0.7 T at , irreversible temperature behavior of
magnetization and resistivity were found . The obtained data were explained in
terms of degenerate tight binding model using random phase approximation. The
contribution of holes in and bands of manganese ions to the
conductivity, optical absorbtion spectra and charge instability in were studied. Charge susceptibility maxima resulted from the competition of
the on-site Coulomb interaction between the holes in different orbitals and
small hybridization of sub-bands were calculated at .Comment: 6 pages, 12 figure
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