1,271 research outputs found
Topological Landau-Ginzburg theory with a rational potential and the dispersionless KP hierarchy
Based on the dispersionless KP (dKP) theory, we give a comprehensive study of
the topological Landau-Ginzburg (LG) theory characterized by a rational
potential. Writing the dKP hierarchy in a general form, we find that the
hierarchy naturally includes the dispersionless (continuous) limit of Toda
hierarchy and its generalizations having finite number of primaries. Several
flat solutions of the topological LG theory are obtained in this formulation,
and are identified with those discussed by Dubrovin. We explicitly construct
gravitational descendants for all the primary fields. Giving a residue formula
for the 3-point functions of the fields, we show that these 3-point functions
satisfy the topological recursion relation. The string equation is obtained as
the generalized hodograph solutions of the dKP hierarchy, which show that all
the gravitational effects to the constitutive equations (2-point functions) can
be renormalized into the coupling constants in the small phase space.Comment: 54 pages, Plain TeX. Figure could be obtained from Kodam
Redshift Dependent Lag-Luminosity Relation in 565 BASTE Gamma Ray Bursts
We compared redshifts from Yonetoku relation and from the
lag-luminosity relation for 565 BASTE GRBs and were surprised to find that the
correlation is very low. Assuming that the luminosity is a function of both
and the intrinsic spectral lag , we found a new redshift
dependent lag-luminosity relation as with the correlation coefficient of 0.77
and the chance probability of . To check the validity of
this method, we examined the other luminosity indicator, Amati relation, using
and the observed fluence and found the correlation coefficient of 0.92
and the chance probability of . Although the spectral lag
is computed from two channels of BATSE, our new lag-luminosity relation
suggests that a possible lag-luminosity relation in the \swift era should also
depend on redshift
Evolution of non-linear cosmological perturbations
We define fully non-perturbative generalizations of the uniform density and
comoving curvature perturbations, which are known, in the linear theory, to be
conserved on sufficiently large scales for adiabatic perturbations. Our
non-linear generalizations are defined geometrically, independently of any
coordinate system. We give the equations governing their evolution on all
scales. Also, in order to make contact with previous works on first and second
order perturbations, we introduce a coordinate system and show that previous
results can be recovered, on large scales, in a remarkably simple way, after
restricting our definitions to first and second orders in a perturbative
expansion.Comment: 4 pages, version published in PRL 95, 091303 (2005
An overview of the Riemannian metrics on spaces of curves using the Hamiltonian approach
Here shape space is either the manifold of simple closed smooth
unparameterized curves in or is the orbifold of immersions from
to modulo the group of diffeomorphisms of . We
investige several Riemannian metrics on shape space: -metrics weighted by
expressions in length and curvature. These include a scale invariant metric and
a Wasserstein type metric which is sandwiched between two length-weighted
metrics. Sobolev metrics of order on curves are described. Here the
horizontal projection of a tangent field is given by a pseudo-differential
operator. Finally the metric induced from the Sobolev metric on the group of
diffeomorphisms on is treated. Although the quotient metrics are
all given by pseudo-differential operators, their inverses are given by
convolution with smooth kernels. We are able to prove local existence and
uniqueness of solution to the geodesic equation for both kinds of Sobolev
metrics.
We are interested in all conserved quantities, so the paper starts with the
Hamiltonian setting and computes conserved momenta and geodesics in general on
the space of immersions. For each metric we compute the geodesic equation on
shape space. In the end we sketch in some examples the differences between
these metrics.Comment: 46 pages, some misprints correcte
Large-scale cosmological perturbations on the brane
In brane-world cosmologies of Randall-Sundrum type, we show that evolution of
large-scale curvature perturbations may be determined on the brane, without
solving the bulk perturbation equations. The influence of the bulk
gravitational field on the brane is felt through a projected Weyl tensor which
behaves effectively like an imperfect radiation fluid with anisotropic stress.
We define curvature perturbations on uniform density surfaces for both the
matter and Weyl fluids, and show that their evolution on large scales follows
directly from the energy conservation equations for each fluid. The total
curvature perturbation is not necessarily constant for adiabatic matter
perturbations, but can change due to the Weyl entropy perturbation. To relate
this curvature perturbation to the longitudinal gauge metric potentials
requires knowledge of the Weyl anisotropic stress which is not determined by
the equations on the brane. We discuss the implications for large-angle
anisotropies on the cosmic microwave background sky.Comment: 13 pages, latex with revtex, no figure
On the evolution and environmental dependence of the star formation rate versus stellar mass relation since z ˜ 2.
This paper discusses the evolution of the correlation between galaxy star formation rates (SFRs) and stellar mass (M*) over the last ∼10 Gyr, particularly focusing on its environmental dependence. We first present the mid-infrared (MIR) properties of the Hα-selected galaxies in a rich cluster Cl 0939+4713 at z = 0.4. We use wide-field Spitzer/MIPS 24 μm data to show that the optically red Hα emitters, which are most prevalent in group-scale environments, tend to have higher SFRs and higher dust extinction than the majority population of blue Hα sources. With an MIR stacking analysis, we find that the median SFR of Hα emitters is higher in higher density environment at z = 0.4. We also find that star-forming galaxies in high-density environment tend to have higher specific SFR (SSFR), although the trend is much less significant compared to that of SFR. This increase of SSFR in high-density environment is not visible when we consider the SFR derived from Hα alone, suggesting that the dust attenuation in galaxies depends on environment; galaxies in high-density environment tend to be dustier (by up to ∼0.5 mag), probably reflecting a higher fraction of nucleated, dusty starbursts in higher density environments at z = 0.4. We then discuss the environmental dependence of the SFR–M* relation for star-forming galaxies since z ∼ 2, by compiling our comparable, narrow-band-selected, large Hα emitter samples in both distant cluster environments and field environments. We find that the SSFR of Hα-selected galaxies (at the fixed mass of log (M*/M⊙) = 10) rapidly evolves as (1 + z)3, but the SFR–M* relation is independent of the environment since z ∼ 2, as far as we rely on the Hα-based SFRs (with M*-dependent extinction correction). Even if we consider the possible environmental variation in the dust attenuation, we conclude that the difference in the SFR–M* relation between cluster and field star-forming galaxies is always small (≲0.2 dex level) at any time in the history of the Universe since z ∼ 2
The failure of cosmological perturbation theory in the new ekpyrotic and cyclic ekpyrotic scenarios
Cosmological perturbation theory fails in the new ekpyrotic and cyclic
ekpyrotic scenarios, before the scale factor of the Universe reaches zero. As a
result, a recently-proposed recipe for evolving the curvature perturbation
through the bounce in these scenarios cannot be justified.Comment: 10 pages. v2: Logic of the demonstration of non-linearity stated more
explicitely. Remarks on non-singular bounces removed for inclusion in a later
paper. v3: As accepted by Phys Lett B v4: Comment on the paper of Banks and
Fischler removed following its withdrawal; more precise abstrac
An Observational Test of Two-field Inflation
We study adiabatic and isocurvature perturbation spectra produced by a period
of cosmological inflation driven by two scalar fields. We show that there
exists a model-independent consistency condition for all two-field models of
slow-roll inflation, despite allowing for model-dependent linear processing of
curvature and isocurvature perturbations during and after inflation on
super-horizon scales. The scale-dependence of all spectra are determined solely
in terms of slow-roll parameters during inflation and the dimensionless
cross-correlation between curvature and isocurvature perturbations. We present
additional model-dependent consistency relations that may be derived in
specific two-field models, such as the curvaton scenario.Comment: 6 pages, latex with revtex, no figures; v2, minor changes, to appear
in Physical Review
Establishment of a monoclonal antibody for human LXRα: Detection of LXRα protein expression in human macrophages
Liver X activated receptor alpha (LXRα) forms a functional dimeric nuclear receptor with RXR that regulates the metabolism of several important lipids, including cholesterol and bile acids. As compared with RXR, the LXRα protein level in the cell is low and the LXRα protein itself is very hard to detect. We have previously reported that the mRNA for LXRα is highly expressed in human cultured macrophages. In order to confirm the presence of the LXRα protein in the human macrophage, we have established a monoclonal antibody against LXRα, K-8607. The binding of mAb K-8607 to the human LXRα protein was confirmed by a wide variety of different techniques, including immunoblotting, immunohistochemistry, and electrophoretic mobility shift assay (EMSA). By immunoblotting with this antibody, the presence of native LXR protein in primary cultured human macrophage was demonstrated, as was its absence in human monocytes. This monoclonal anti-LXRα antibody should prove to be a useful tool in the analysis of the human LXRα protein
Comments on gauge-invariance in cosmology
We revisit the gauge issue in cosmological perturbation theory, and highlight
its relation to the notion of covariance in general relativity. We also discuss
the similarities and differences of the covariant approach in perturbation
theory to the Bardeen or metric approach in a non-technical fashion.Comment: 7 pages, 1 figure, revtex4; v3: minor changes, typos corrected,
discussion extended; v4: typos corrected, corresponding to published versio
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