84 research outputs found
Formation and evolution of the protoplanetary disk
A disk formation model during collapse of the protosolar nebula, yielding a low-mass protoplanetary disk is presented. The following subject areas are covered: (1) circumstellar disks; (2) conditions for the formation of stars with disks; (3) early evolution of the protoplanetary disk; and (4) temperature conditions and the convection in the protoplanetary disk
Expansionfree Fluid Evolution and Skripkin Model in f(R) Theory
We consider the modified theory of gravity whose higher order
curvature terms are interpreted as a gravitational fluid or dark source. The
gravitational collapse of a spherically symmetric star, made up of locally
anisotropic viscous fluid, is studied under the general influence of the
curvature fluid. Dynamical equations and junction conditions are modified in
the context of f(R) dark energy and by taking into account the expansionfree
evolution of the self-gravitating fluid. As a particular example, the Skripkin
model is investigated which corresponds to isotropic pressure with constant
energy density. The results are compared with corresponding results in General
Relativity.Comment: 18 pages, accepted for publication Int. J. Mod. Phys.
Spin Glass Computations and Ruelle's Probability Cascades
We study the Parisi functional, appearing in the Parisi formula for the
pressure of the SK model, as a functional on Ruelle's Probability Cascades
(RPC). Computation techniques for the RPC formulation of the functional are
developed. They are used to derive continuity and monotonicity properties of
the functional retrieving a theorem of Guerra. We also detail the connection
between the Aizenman-Sims-Starr variational principle and the Parisi formula.
As a final application of the techniques, we rederive the Almeida-Thouless line
in the spirit of Toninelli but relying on the RPC structure.Comment: 20 page
Deep connection between f(R) gravity and the interacting dark sector model
We examine the conformal equivalence between the gravity and the
interacting dark sector model. We review the well-known result that the
conformal transformation physically corresponds to the mass dilation which
marks the strength of interaction between dark sectors. Instead of modeling
f(R) gravity in the Jordan frame, we construct the gravity in terms of
mass dilation function in the Einstein frame. We find that the condition to
keep gravity consistent with CMB observations ensures the energy flow
from dark energy to dark matter in the corresponding interacting model, which
meets the requirement to alleviate the coincidence problem in the Einstein
framework.Comment: 9 pages, 2 figures, revised version, accepted for publication in
Phys. Rev.
Random matrices: Universality of local eigenvalue statistics up to the edge
This is a continuation of our earlier paper on the universality of the
eigenvalues of Wigner random matrices. The main new results of this paper are
an extension of the results in that paper from the bulk of the spectrum up to
the edge. In particular, we prove a variant of the universality results of
Soshnikov for the largest eigenvalues, assuming moment conditions rather than
symmetry conditions. The main new technical observation is that there is a
significant bias in the Cauchy interlacing law near the edge of the spectrum
which allows one to continue ensuring the delocalization of eigenvectors.Comment: 24 pages, no figures, to appear, Comm. Math. Phys. One new reference
adde
On analytical solutions of f(R) modified gravity theories in FLRW cosmologies
A novel analytical method for f(R) modified theories without matter in
Friedmann-Lemaitre-Robertson-Walker spacetimes is introduced. The equation of
motion for the scale factor in terms of cosmic time is reduced to the equation
for the evolution of the Ricci scalar R with the Hubble parameter H. The
solution of equation of motion for actions of the form of power law in Ricci
scalar R, is presented with a detailed elaboration of the action quadratic in
R. The reverse use of the introduced method is exemplified in finding
functional forms f(R) which lead to specified scale factor functions. The
analytical solutions are corroborated by numerical calculations with excellent
agreement. Possible further applications to the phases of inflationary
expansion and late-time acceleration as well as f(R) theories with radiation
are outlined.Comment: 16 pages, 6 figures. v2: minor changes, references added. v3: minor
changes, more references added. v4: version to appear in IJMPD. v5: DOI and
journal reference adde
Excitation of MHD waves in magnetized anisotropic cosmologies
The excitation of cosmological perturbations in an anisotropic cosmological
model and in the presence of a homogeneous magnetic field was studied, using
the resistive magnetohydrodynamic (MHD) equations. We have shown that
fast-magnetosonic modes, propagating normal to the magnetic field grow
exponentially and saturated at high values, due to the resistivity. We also
demonstrate that the jeans-like instabilities are enhanced inside a resistive
and the formation of condensations formed within an anisotropic fluid influence
the growing magnetosonic waves.Comment: 12 pages, RevTex, 5 figures ps, accepted for publication to Astronomy
and Astrophysic
Dynamics of Circumstellar Disks II: Heating and Cooling
We present a series of 2-d () hydrodynamic simulations of marginally
self gravitating disks around protostars using an SPH code. We implement simple
dynamical heating and we cool each location as a black body, using a
photosphere temperature obtained from the local vertical structure. We
synthesize SEDs from our simulations and compare them to fiducial SEDs derived
from observed systems. These simulations produce less distinct spiral structure
than isothermally evolved systems, especially in the inner third of the disk.
Pattern are similar further from the star but do not collapse into condensed
objects. The photosphere temperature is well fit to a power law in radius with
index , which is very steep. Far from the star, internal heating
( work and shocks) are not responsible for generating a large fraction of
the thermal energy contained in the disk matter. Gravitational torques
responsible for such shocks cannot transport mass and angular momentum
efficiently in the outer disk. Within 5--10 AU of the star, rapid break
up and reformation of spiral structure causes shocks, which provide sufficient
dissipation to power a larger fraction of the near IR energy output. The
spatial and size distribution of grains can have marked consequences on the
observed near IR SED and can lead to increased emission and variability on
year time scales. When grains are vaporized they do not reform
into a size distribution similar to that from which most opacity calculations
are based. With rapid grain reformation into the original size distribution,
the disk does not emit near infrared photons. With a plausible modification to
the opacity, it contributes much more.Comment: Accepted by ApJ, 60pg incl 24 figure
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