CP Violation and Moduli Stabilization in Heterotic Models

The role of moduli stabilization in predictions for CP violation is examined in the context of four-dimensional effective supergravity models obtained from the weakly coupled heterotic string. We point out that while stabilization of compactification moduli has been studied extensively, the determination of background values for other scalars by dynamical means has not been subjected to the same degree of scrutiny. These other complex scalars are important potential sources of CP violation and we show in a simple model how their background values (including complex phases) may be determined from the minimization of the supergravity scalar potential, subject to the constraint of vanishing cosmological constant.Comment: 8 Pages. Based on a talk given at the CP Violation Conference, University of Michigan, Ann Arbor, November 4-18, 2001, correction to Eq. (27

Molecular dynamics simulations of the evaporation of particle-laden droplets

We use molecular dynamics simulations to study the evaporation of particle-laden droplets on a heated surface. The droplets are composed of a Lennard-Jones fluid containing rigid particles which are spherical sections of an atomic lattice, and heating is controlled through the temperature of an atomistic substrate. We observe that sufficiently large (but still nano-sized) particle-laden drops exhibit contact line pinning, measure the outward fluid flow field which advects particle to the drop rim, and find that the structure of the resulting aggregate varies with inter-particle interactions. In addition, the profile of the evaporative fluid flux is measured with and without particles present, and is also found to be in qualitative agreement with earlier theory. The compatibility of simple nanoscale calculations and micron-scale experiments indicates that molecular simulation may be used to predict aggregate structure in evaporative growth processes

Observers can always generate nonlocal correlations without aligning measurements by covering all their bases

Quantum theory allows for correlations between the outcomes of distant measurements that are inconsistent with any locally causal theory, as demonstrated by the violation of a Bell inequality. Typical demonstrations of these correlations require careful alignment between the measurements, which requires distant parties to share a reference frame. Here, we prove, following a numerical observation by Shadbolt et al., that if two parties share a Bell state and each party randomly chooses three orthogonal measurements, then the parties will always violate a Bell inequality. Furthermore, we prove that this probability is highly robust against local depolarizing noise, in that small levels of noise only decrease the probability of violating a Bell inequality by a small amount. We also show that generalizing to N parties increases the robustness against noise. These results improve on previous ones that only allowed a high probability of violating a Bell inequality for large numbers of parties.Comment: 4 pages, 2 figures. v2: updated reference. v3: published versio

A survey of the properties of early-type galaxies

A compilation of the properties of elliptical and early disk galaxies was completed. In addition to material from the literature, such as Infrared Astronomy Satellite (IRAS) fluxes, the compilation includes recent measurements of HI and CO, as well as a review of the x ray properties by Forman and Jones. The data are used to evaluate the gas content of early systems and to search for correlations with x ray emission. The interstellar medium in early-type galaxies is generally dominated by hot interstellar gas (T approx. 10 to the 7th power K; c.f. the review by Fabbiano 1989 and references therein). In addition, a significant fraction of these galaxies show infrared emission (Knapp, et al., 1989), optical emission lines, and visible dust. Sensitive studies in HI and CO of a number of these galaxies have been completed recently, resulting in several detections, particularly of the later types. Researchers wish to understand the connection among these different forms of the interstellar medium, and to examine the theoretical picture of the fate of the hot gas. To do so, they compiled observations of several forms of interstellar matter for a well-defined sample of early-type galaxies. Here they present a statistical analysis of this data base and discuss the implications of the results

Shear flow pumping in open microfluidic systems

We propose to drive open microfluidic systems by shear in a covering fluid layer, e.g., oil covering water-filled chemical channels. The advantages as compared to other means of pumping are simpler forcing and prevention of evaporation of volatile components. We calculate the expected throughput for straight channels and show that devices can be built with off-the-shelf technology. Molecular dynamics simulations suggest that this concept is scalable down to the nanoscale.Comment: 4 pages, 4 figure, submitted to Phys. Rev. Let

A Simple Model for Pulse Profiles from Precessing Pulsars, with Special Application to Relativistic Binary PSR B1913+16

We study the observable pulse profiles that can be generated from precessing pulsars. A novel coordinate system is defined to aid visualization of the observing geometry. Using this system we explore the different families of profiles that can be generated by simple, circularly symmetric beam shapes. An attempt is then made to fit our model to the observations of relativistic binary PSR B1913+16. It is found that while qualitatively similar pulse profiles can be produced, this minimal model is insufficient for an accurate match to the observational data. Consequently, we confirm that the emission beam of PSR B1913+16 must deviate from circular symmetry, as first reported by Weisberg and Taylor. However, the approximate fits obtained suggest that it may be sufficient to consider only minimal deviations from a circular beam in order to explain the data. We also comment on the applicability of our analysis technique to other precessing pulsars, both binary and isolated.Comment: 35 pages and 8 figures. Published versio

Nonnegative subtheories and quasiprobability representations of qubits

Negativity in a quasiprobability representation is typically interpreted as an indication of nonclassical behavior. However, this does not preclude states that are non-negative from exhibiting phenomena typically associated with quantum mechanics - the single qubit stabilizer states have non-negative Wigner functions and yet play a fundamental role in many quantum information tasks. We seek to determine what other sets of quantum states and measurements for a qubit can be non-negative in a quasiprobability representation, and to identify nontrivial unitary groups that permute the states in such a set. These sets of states and measurements are analogous to the single qubit stabilizer states. We show that no quasiprobability representation of a qubit can be non-negative for more than four bases and that the non-negative bases in any quasiprobability representation must satisfy certain symmetry constraints. We provide an exhaustive list of the sets of single qubit bases that are non-negative in some quasiprobability representation and are also permuted by a nontrivial unitary group. This list includes two families of three bases that both include the single qubit stabilizer states as a special case and a family of four bases whose symmetry group is the Pauli group. For higher dimensions, we prove that there can be no more than 2^{d^2} states in non-negative bases of a d-dimensional Hilbert space in any quasiprobability representation. Furthermore, these bases must satisfy certain symmetry constraints, corresponding to requiring the bases to be sufficiently complementary to each other.Comment: 17 pages, 8 figures, comments very welcome; v2 published version. Note that the statement and proof of Theorem III.2 in the published version are incorrect (an erratum has been submitted), and this arXiv version (v2) presents the corrected theorem and proof. The conclusions of the paper are unaffected by this correctio

Quasinormal Modes and Stability Criterion of Dilatonic Black Hole in 1+1 and 4+1 Dimensions

We study the stability of black holes that are solutions of the dilaton gravity derived from string-theoretical models in two and five dimensions against to scalar field perturbations, using the Quasinormal Modes (QNMs) approach. In order to find the QNMs corresponding to a black hole geometry, we consider perturbations described by a massive scalar field non-minimally coupled to gravity. We find that the QNM's frequencies turn out to be pure imaginary leading to purely damped modes, that is in agreement with the literature of dilatonic black holes. Our result exhibits the unstable behavior of the considered geometry against the scalar perturbations. We consider both the minimal coupling case, i.e., for which the coupling parameter $\zeta$ vanishes, and the case $\zeta={1/4}$.Comment: sevarl changes, some reference was added, 10 pages, 4 figure