Coherent macroscopic quantum tunneling in boson-fermion mixtures

We show that the cold atom systems of simultaneously trapped Bose-Einstein condensates (BEC's) and quantum degenerate fermionic atoms provide promising laboratories for the study of macroscopic quantum tunneling. Our theoretical studies reveal that the spatial extent of a small trapped BEC immersed in a Fermi sea can tunnel and coherently oscillate between the values of the separated and mixed configurations (the phases of the phase separation transition of BEC-fermion systems). We evaluate the period, amplitude and dissipation rate for $^{23}$Na and $^{40}$K-atoms and we discuss the experimental prospects for observing this phenomenon.Comment: 4 pages, 3 figure

Small polarons in dilute gas Bose-Einstein condensates

A neutral impurity atom immersed in a dilute Bose-Einstein condensate (BEC) can have a bound ground state in which the impurity is self-localized. In this small polaron-like state, the impurity distorts the density of the surrounding BEC, thereby creating the self-trapping potential minimum. We describe the self-localization in a strong coupling approach

Modulational instability criteria for two-component Bose-Einstein condensates

The stability of colliding Bose-Einstein condensates is investigated. A set of coupled Gross-Pitaevskii equations is thus considered, and analyzed via a perturbative approach. No assumption is made on the signs (or magnitudes) of the relevant parameters like the scattering lengths and the coupling coefficients. The formalism is therefore valid for asymmetric as well as symmetric coupled condensate wave states. A new set of explicit criteria is derived and analyzed. An extended instability region, in addition to an enhanced instability growth rate is predicted for unstable two component bosons, as compared to the individual (uncoupled) state.Comment: 4 pages, 1 figur

Multiple mating in the ant Cataglyphis cursor: testing the sperm limitation and the diploid male load hypotheses

Abstract.: Multiple mating (i.e., polyandry) by queens in social Hymenoptera is expected to weaken social cohesion since it lowers within-colony relatedness, and hence, indirect fitness benefits from kin selection. Yet, there are many species where queens mate multiply. Several hypotheses have been put forward to explain the evolution and maintenance of polyandry. Here,we investigated the ‘sperm limitation' and the ‘diploid male load' hypotheses in the ant Cataglyphis cursor. Genetic analyses of mother-offspring combinations showed that queens mate with up to 8 males, with an effective mating frequency of 3.79. Significant paternity skew (unequal contribution of the fathers) was detected in 1 out of 5 colonies. The amount of sperm stored in the spermatheca was not correlated with the queen mating frequency, and males carry on average enough sperm in their seminal vesicles to fill one queen's spermatheca. Analyses of the nuclear DNA-content of males also revealed that all were haploid. These results suggest that the ‘sperm limitation' and the ‘diploid male load' hypotheses are unlikely to account for the queen mating frequency reported in this ant. In light of our results and the life-history traits of C. cursor, we discuss alternative hypotheses to account for the adaptive significance of multiple mating by queens in this specie

Acoustic attenuation probe for fermion superfluidity in ultracold atom gases

Dilute gas Bose-Einstein condensates (BEC's), currently used to cool fermionic atoms in atom traps, can also probe the superfluidity of these fermions. The damping rate of BEC-acoustic excitations (phonon modes), measured in the middle of the trap as a function of the phonon momentum, yields an unambiguous signature of BCS-like superfluidity, provides a measurement of the superfluid gap parameter and gives an estimate of the size of the Cooper-pairs in the BEC-BCS crossover regime. We also predict kinks in the momentum dependence of the damping rate which can reveal detailed information about the fermion quasi-particle dispersion relation.Comment: 4 pages, 2 figures. Revised versio

The Effects of Statistical Information on Risk- and Ambiguity-Attitudes, and on Rational Insurance Decisions

This is a preprint of an article to be published in Management ScienceThis paper examines the effects of statistical information about risks on risk attitudes and demand for insurance. A descriptive purpose is to obtain new insights into risk and ambiguity attitudes of the general public. A prescriptive purpose is to provide recommendations for the provision of risk information to individuals so as to help them choose their most preferred options. In an experiment, N = 476 clients of a Dutch health insurance company were given various forms of statistical information about health expenses. Average population-cost information generally increased the willingness to take insurance. Own past-costs information differentiated betwee individuals, increasing the willingness to take insurance for high-cost and risk averse clients but not for others. Detailed cost information reinforced the effects of total-cost information. Prescriptively, the drawback of adverse selection must be weighed against a desirable interaction with risk attitude, increased customer satisfaction, and increased cost awareness. Descriptively, ambiguity preference was found rather than aversion, and no risk aversion was found for loss outcomes. Both findings, obtained in a natural decision context, deviate from traditional views in risk theory but agree with prospect theory

Degenerate fermion gas heating by hole creation

Loss processes that remove particles from an atom trap leave holes behind in the single particle distribution if the trapped gas is a degenerate fermion system. The appearance of holes increases the temperature and we show that the heating is (i) significant if the initial temperature is well below the Fermi temperature $T_{F}$, and (ii) increases the temperature to $T \geq T_{F}/4$ after half of the system's lifetime, regardless of the initial temperature. The hole heating has important consequences for the prospect of observing Cooper-pairing in atom traps.Comment: to be published in PR

Model-independent view on the low-mass proton-antiproton enhancement

We present a simple interpretation of the recently observed near-threshold proton-antiproton enhancement. It is described by a set of low-energy parameters deduced from the analysis of NantiN experiments at LEAR. We predict a related effect in photoproduction reaction under study by CLAS collaboration.Comment: 10 pages, 2 figure

Electric Dipole Moments of Light Nuclei From Chiral Effective Field Theory

We set up the framework for the calculation of electric dipole moments (EDMs) of light nuclei using the systematic expansion provided by chiral effective field theory (EFT). We take into account parity (P) and time-reversal (T) violation which, at the quark-gluon level, originates from the QCD vacuum angle and dimension-six operators capturing physics beyond the Standard Model. We argue that EDMs of light nuclei can be expressed in terms of six low-energy constants that appear in the P- and T-violating nuclear potential and electric current. As examples, we calculate the EDMs of the deuteron, the triton, and 3He in leading order in the EFT expansion

Phylogeny of the Hawkmoth tribe Ambulycini: mitogenomes from museum specimens resolve major relationships

Ambulycini are a cosmopolitan tribe of the moth family Sphingidae, comprised of ten genera, three of which are found in tropical Asia, four in the Neotropics, one in Africa, one in the Middle East and one restricted to the islands of New Caledonia. Recent phylogenetic analyses of the tribe have yielded conflicting results, and some have suggested a close relationship of the monobasic New Caledonian genus Compsulyx Holloway, 1979 to the Neotropical ones, despite being found on opposite sides of the Pacific Ocean. Here we investigate relationships within the tribe using full mitochondrial genomes, mainly derived from dry-pinned museum collections material. Mitogenomic data were obtained for 19 species representing nine of the ten Ambulycini genera. Phylogenetic trees are in agreement with a tropical Asian origin for the tribe. Furthermore, results indicate that the Neotropical genus Adhemarius Oiticica Filho, 1939 is paraphyletic and support the notion that Orecta Rothschild & Jordan 1903 and Trogolegnum Rothschild & Jordan, 1903 may need to be synonymized. Finally, in our analysis the Neotropical genera do not collectively form a monophyletic group, due to a clade comprising the New Caledonian genus Compsulyx and the African genus Batocnema Rothschild & Jordan, 1903 being placed as sister to the Neotropical genus Protambulyx Rothschild & Jordan, 1903. This finding implies a complex biogeographic history and suggests the evolution of the tribe involved at least two long-distance dispersal events