Leptogenesis from Pseudo-Scalar Driven Inflation

We examine recent claims for a considerable amount of leptogenesis, in some inflationary scenarios, through the gravitational anomaly in the lepton number current. We find that when the short distances contributions are properly included the amount of lepton number generated is actually much smaller.Comment: JHEP style, 11 pages. Corrected typ

On the Initial Conditions for Brane Inflation

String theory gives rise to various mechanisms to generate primordial inflation, of which ``brane inflation'' is one of the most widely considered. In this scenario, inflation takes place while two branes are approaching each other, and the modulus field representing the separation between the branes plays the role of the inflaton field. We study the phase space of initial conditions which can lead to a sufficiently long period of cosmological inflation, and find that taking into account the possibility of nonvanishing initial momentum can significantly change the degree of fine tuning of the required initial conditions.Comment: 11 pages, 2 figure

Absence of self-averaging in the complex admittance for transport through random media

A random walk model in a one dimensional disordered medium with an oscillatory input current is presented as a generic model of boundary perturbation methods to investigate properties of a transport process in a disordered medium. It is rigorously shown that an admittance which is equal to the Fourier-Laplace transform of the first-passage time distribution is non-self-averaging when the disorder is strong. The low frequency behavior of the disorder-averaged admittance, $-1 \sim \omega^{\mu}$ where $\mu < 1$, does not coincide with the low frequency behavior of the admittance for any sample, $\chi - 1 \sim \omega$. It implies that the Cole-Cole plot of $$ appears at a different position from the Cole-Cole plots of $\chi$ of any sample. These results are confirmed by Monte-Carlo simulations.Comment: 7 pages, 2 figures, published in Phys. Rev.

Inflation and Brane Gases

We investigate a new way of realizing a period of cosmological inflation in the context of brane gas cosmology. It is argued that a gas of co-dimension one branes, out of thermal equilibrium with the rest of the matter, has an equation of state which can - after stabilization of the dilaton - lead to power-law inflation of the bulk. The most promising implementation of this mechanism might be in Type IIB superstring theory, with inflation of the three large spatial dimensions triggered by ``stabilized embedded 2-branes''. Possible applications and problems with this proposal are discussed.Comment: 7 pages, uses REVTeX, version to appear in Phys. Rev.

Survival and residence times in disordered chains with bias

We present a unified framework for first-passage time and residence time of random walks in finite one-dimensional disordered biased systems. The derivation is based on exact expansion of the backward master equation in cumulants. The dependence on initial condition, system size, and bias strength is explicitly studied for models with weak and strong disorder. Application to thermally activated processes is also developed.Comment: 13 pages with 2 figures, RevTeX4; v2:minor grammatical changes, typos correcte

Can the clustered dark matter and the smooth dark energy arise from the same scalar field ?

Cosmological observations suggest the existence of two different kinds of energy densities dominating at small ($\lesssim 500$ Mpc) and large ($\gtrsim 1000$ Mpc) scales. The dark matter component, which dominates at small scales, contributes $\Omega_m \approx 0.35$ and has an equation of state $p=0$ while the dark energy component, which dominates at large scales, contributes $\Omega_V \approx 0.65$ and has an equation of state $p\simeq -\rho$. It is usual to postulate wimps for the first component and some form of scalar field or cosmological constant for the second component. We explore the possibility of a scalar field with a Lagrangian L =- V(\phi) \sqrt{1 - \del^i \phi \del_i \phi} acting as {\it both} clustered dark matter and smoother dark energy and having a scale dependent equation of state. This model predicts a relation between the ratio $r = \rho_V/\rho_{\rm DM}$ of the energy densities of the two dark components and expansion rate $n$ of the universe (with $a(t) \propto t^n$) in the form $n = (2/3) (1+r)$. For $r \approx 2$, we get $n \approx 2$ which is consistent with observations.Comment: Revised to match the published version. Minor changes and a reference adde

Supersymmetry Breaking and Dilaton Stabilization in String Gas Cosmology

In this Note we study supersymmetry breaking via gaugino condensation in string gas cosmology. We show that the same gaugino condensate which is introduced to stabilize the dilaton breaks supersymmetry. We study the constraints on the scale of supersymmetry breaking which this mechanism leads to.Comment: 11 page

Transverse Spin at PHENIX: Results and Prospects

The Relativistic Heavy Ion Collider (RHIC), as the world's first and only polarized proton collider, offers a unique environment in which to study the spin structure of the proton. In order to study the proton's transverse spin structure, the PHENIX experiment at RHIC took data with transversely polarized beams in 2001-02 and 2005, and it has plans for further running with transverse polarization in 2006 and beyond. Results from early running as well as prospective measurements for the future will be discussed.Comment: 6 pages, 2 figures, presented at Transversity 2005, Como, Ital

Did Galaxy Assembly and Supermassive Black-Hole Growth go hand-in-hand?

In this paper, we address whether the growth of supermassive black-holes has kept pace with the process of galaxy assembly. For this purpose, we first searched the Hubble Ultra Deep Field (HUDF) for "tadpole galaxies", which have a knot at one end and an extended tail. They appear dynamically unrelaxed -- presumably early-stage mergers -- and make up ~6% of the field galaxy population. Their redshift distribution follows that of field galaxies, indicating that -- if tadpole galaxies are indeed dynamically young -- the process of galaxy assembly generally kept up with the reservoir of field galaxies as a function of epoch. Next, we present a search for HUDF objects with point-source components that are optically variable (at the >~3.0 sigma level) on timescales of weeks--months. Among 4644 objects to i_AB=28.0 mag (10 sigma), 45 have variable point-like components, which are likely weak AGN. About 1% of all field objects show variability for 0.1 < z < 4.5, and their redshift distribution is similar to that of field galaxies. Hence supermassive black-hole growth in weak AGN likely also kept up with the process of galaxy assembly. However, the faint AGN sample has almost no overlap with the tadpole sample, which was predicted by recent hydrodynamical numerical simulations. This suggests that tadpole galaxies are early-stage mergers, which likely preceded the ``turn-on'' of the AGN component and the onset of visible point-source variability by >~1 Gyr.Comment: 9 pages, Latex2e requires 'elsart' and 'elsart3' (included), 10 postscript figures. To appear in the Proceedings of the Leiden Workshop on "QSO Host Galaxies: Evolution and Environment", eds. P.D. Barthel & D.B. Sanders (New Astron. Rev., 2006

Variable-Speed-of-Light Cosmology from Brane World Scenario

We argue that the four-dimensional universe on the TeV brane of the Randall-Sundrum scenario takes the bimetric structure of Clayton and Moffat, with gravitons traveling faster than photons instead, while the radion varies with time. We show that such brane world bimetric model can thereby solve the flatness and the cosmological constant problems, provided the speed of a graviton decreases to the present day value rapidly enough. The resolution of other cosmological problems such as the horizon problem and the monopole problem requires supplementation by inflation, which may be achieved by the radion field provided the radion potential satisfies the slow-roll approximation.Comment: 18 pages, LaTeX, revised version to appear in Phys. Rev.