Dyon Spectrum in CHL Models

We propose a formula for the degeneracy of quarter BPS dyons in a class of CHL models. The formula uses a modular form of a subgroup of the genus two modular group Sp(2,Z). Our proposal is S-duality invariant and reproduces correctly the entropy of a dyonic black hole to first non-leading order for large values of the charges.Comment: LaTeX file, 38 pages, minor changes in section 3.3(v2), minor changes in introduction, appendix A and C(v3

Alignment and orientation of an adsorbed dipole molecule

Half-cycle laser pulse is applied on an absorbed molecule to investigate its alignment and orientation behavior. Crossover from field-free to hindered rotation motion is observed by varying the angel of hindrance of potential well. At small hindered angle, both alignment and orientation show sinusoidal-like behavior because of the suppression of higher excited states. However, mean alignment decreases monotonically as the hindered angle is increased, while mean orientation displays a minimum point at certain hindered angle. The reason is attributed to the symmetry of wavefunction and can be explained well by analyzing the coefficients of eigenstates.Comment: 4 pages, 4 figures, to appear in Phys. Rev. B (2004

Evidence for an intermediate mass black hole and a multi-zone warm absorber in NGC 4395

We report on the results of an analysis in the X-ray band of a recent long ASCA observation of NGC 4395, the most variable low-luminosity AGN known. A relativistically-broadened iron line at ~6.4 keV is clearly resolved in the time-averaged spectrum, with an equivalent width of 310^{+70}_{-90} eV. Time-resolved spectral analysis of the heavily absorbed soft X-ray band confirms the existence of a variable, multi-zone warm absorber in this source, as proposed in a previous analysis of a shorter ASCA observation. The light curve of the source is wildly variable on timescales of hours or less, and a factor of nearly 10 change in count-rate was recorded in a period of less than 2000 s. The long observation and variability of the source allowed the power density spectrum (PDS) to be constructed to an unprecedented level of detail. There is evidence for a break in the PDS from a slope of \alpha~1 to \alpha~1.8 at a frequency of around 3 \times 10^{-4} Hz. The central black hole mass of NGC 4395 is estimated to be approximately 10^4-10^5 solar masses using the break in the PDS, a result consistent with previous analyses using optical and kinematical techniques.Comment: 8 pages, 6 figures, accepted for publication in MNRA

CHL Dyons and Statistical Entropy Function from D1-D5 System

We give a proof of the recently proposed formula for the dyon spectrum in CHL string theories by mapping it to a configuration of D1 and D5-branes and Kaluza-Klein monopole. We also give a prescription for computing the degeneracy as a systematic expansion in inverse powers of charges. The computation can be formulated as a problem of extremizing a duality invariant statistical entropy function whose value at the extremum gives the logarithm of the degeneracy. During this analysis we also determine the locations of the zeroes and poles of the Siegel modular forms whose inverse give the dyon partition function in the CHL models.Comment: LaTeX file, 48 pages; v2: typos correcte

Pseudomoduli Dark Matter

We point out that pseudomoduli -- tree-level flat directions that often accompany dynamical supersymmetry breaking -- can be natural candidates for TeV-scale dark matter in models of gauge mediation. The idea is general and can be applied to different dark matter scenarios, including (but not limited to) those of potential relevance to recent cosmic ray anomalies. We describe the requirements for a viable model of pseudomoduli dark matter, and we analyze two example models to illustrate the general mechanism -- one where the pseudomoduli carry Higgsino-like quantum numbers, and another where they are SM singlets but are charged under a hidden-sector $U(1)'$ gauge group.Comment: 20 pages, refs adde

Entanglement creation between two causally-disconnected objects

We study the full entanglement dynamics of two uniformly accelerated Unruh-DeWitt detectors with no direct interaction in between but each coupled to a common quantum field and moving back-to-back in the field vacuum. For two detectors initially prepared in a separable state our exact results show that quantum entanglement between the detectors can be created by the quantum field under some specific circumstances, though each detector never enters the other's light cone in this setup. In the weak coupling limit, this entanglement creation can occur only if the initial moment is placed early enough and the proper acceleration of the detectors is not too large or too small compared to the natural frequency of the detectors. Once entanglement is created it lasts only a finite duration, and always disappears at late times. Prior result by Reznik derived using the time-dependent perturbation theory with extended integration domain is shown to be a limiting case of our exact solutions at some specific moment. In the strong coupling and high acceleration regime, vacuum fluctuations experienced by each detector locally always dominate over the cross correlations between the detectors, so entanglement between the detectors will never be generated.Comment: 16 pages, 8 figures; added Ref.[7] and related discussion

Exact Black Hole Degeneracies and the Topological String

Motivated by the recent conjecture of Ooguri, Strominger and Vafa, we compute the semi-canonical partition function of BPS black holes in N=4 and N=8 string theories, to all orders in perturbation theory. Not only are the black hole partition functions surprisingly simple; they capture the full topological string amplitudes, as expected from the OSV conjecture. The agreement is not perfect, however, as there are differences between the black hole and topological string partition functions even at the perturbative level. We propose a minimal modification of the OSV conjecture, in which these differences are understood as a nontrivial measure factor for the topological string.Comment: 24 page

Characteristic Length Scale of Electric Transport Properties of Genomes

A tight-binding model together with a novel statistical method are used to investigate the relation between the sequence-dependent electric transport properties and the sequences of protein-coding regions of complete genomes. A correlation parameter $\Omega$ is defined to analyze the relation. For some particular propagation length $w_{max}$, the transport behaviors of the coding and non-coding sequences are very different and the correlation reaches its maximal value $\Omega_{max}$. $w_{max}$ and \omax are characteristic values for each species. The possible reason of the difference between the features of transport properties in the coding and non-coding regions is the mechanism of DNA damage repair processes together with the natural selection.Comment: 4 pages, 4 figure