28,718 research outputs found
Towards a warped inflationary brane scanning
We present a detailed systematics for comparing warped brane inflation with
the observations, incorporating the effects of both moduli stabilization and
ultraviolet bulk physics. We explicitly construct an example of the inflaton
potential governing the motion of a mobile D3 brane in the entire warped
deformed conifold. This allows us to precisely identify the corresponding
scales of the cosmic microwave background. The effects due to bulk fluxes or
localized sources are parametrized using gauge/string duality. We next perform
some sample scannings to explore the parameter space of the complete potential,
and first demonstrate that without the bulk effects there can be large
degenerate sets of parameters with observationally consistent predictions. When
the bulk perturbations are included, however, the observational predictions are
generally spoiled. For them to remain consistent, the magnitudes of the bulk
effects need to be highly suppressed via fine tuning.Comment: (v1) 11 pages, 2 figures, 2 tables; (v2) more clarifications and
references added; (v3) 12 pages, more discussions, to appear in Physical
Review
Constraints on a new alternative model to dark energy
The recent type Ia supernova data suggest that the universe is accelerating
now and decelerated in recent past. This may provide the evidence that the
standard Friedmann equation needs to be modified. We analyze in detail a new
model in the context of modified Friedmann equation using the supernova data
published by the High- Supernova Search Team and the Supernova Cosmology
Project. The new model explains recent acceleration and past deceleration.
Furthermore, the new model also gives a decelerated universe in the future.Comment: 12 pages, 5 figures, use ws-ijmpd, minor changes made. In the new
version, a detailed derivation of the model is give
Cosmic Mach Number: A Sensitive Probe for the Growth of Structure
In this Letter, we investigate the potential power of the Cosmic Mach Number
(CMN), which is the ratio between the mean velocity and the velocity dispersion
of galaxies as a function of cosmic scales, to constrain cosmologies. We first
measure the CMN from 5 catalogues of galaxy peculiar velocity surveys at low
redshift (0.002<z<0.03), and use them to contrast cosmological models. Overall,
current data is consistent with the WMAP7 LCDM model. We find that the CMN is
highly sensitive to the growth of structure on scales 0.01<k<0.1 h/Mpc in
Fourier space. Therefore, modified gravity models, and models with massive
neutrinos, in which the structure growth generally deviates from that in the
LCDM model in a scale-dependent way, can be well differentiated from the LCDM
model using future CMN data.Comment: 7 pages, matches the version accepted to JCA
Sexual Bias and Household Consumption: A Semiparametic Analysis of Engel curves in Rural China
We analyze Engel curves for nuclear households in rural China. The sample includes more than 5000 nuclear families covering nineteen out of thirty Chinese provinces. We consider expenditures on food, also subdivided into several food subcategories such as cereals, or meat and fish, and other consumption categories such as alcohol and tobacco, medical, and educational goods. We use the semiparametric partially linear model. This allows for any functional form relationship between the budget shares and total expenditures, but assumes that the demographic variables enter the model in a linear way. We correct for potential endogeneity of total expenditures. Our results suggest that there are economies of scale in families' consumption expenditure patterns. We find some differences in consumption patterns which relate to differences in gender of children, which can be seen as evidence of sexual bias related to a commonly believed existing preference for boys.
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