Effect of Weak Disorder on the BCS-BEC crossover in a two-dimensional Fermi Gas

In this article we study the two-dimensional (2D) ultracold Fermi gas with weak impurity in the framework of mean-field theory where the impurity is introduced through Gaussian fluctuations. We have investigated the role of the impurity by studying the experimentally accessible quantities such as condensate fraction and equation of state of the ultracold systems. Our analysis reveals that, at the crossover the disorder enhances superfluidity, which we attribute to the unique nature of the unitary region and to the dimensional effect.Comment: To appear in Int. J. Mod. Phys.

Investigating Dirty Crossover through Fidelity Susceptibility and Density of States

We investigate the BCS-BEC crossover in an ultracold atomic gas in the presence of disorder. The disorder is incorporated in the mean-field formalism through Gaussian fluctuations. We observe evolution to an asymmetric line-shape of fidelity susceptibility as a function of interaction coupling with increasing disorder strength which may point to an impending quantum phase transition. The asymmetric line-shape is further analyzed using the statistical tools of skewness and kurtosis. We extend our analysis to density of states (DOS) for a better understanding of the crossover in the disordered environment.Comment: 12 pages, 6 figures. To appear in Int. J. Mod. Phys.

Kalb-Ramond field interactions in a braneworld scenario

Electromagnetic and (linearized) gravitational interactions of the Kalb-Ramond (KR) field, derived from an underlying ten dimensional heterotic string in the zero slope limit, are studied in a five dimensional background Randall-Sundrum I spacetime with standard model fields confined to the visible brane having negative tension. The warp factor responsible for generating the gauge hierarchy in the Higgs sector is seen to appear inverted in the KR field couplings, when reduced to four dimensions. This leads to dramatically enhanced rotation, {\it far beyond observational bounds}, of the polarization plane of electromagnetic and gravitational waves, when scattered by a homogeneous KR background. Possible reasons for the conflict between theory and observation are discussed.Comment: 13 pages Latex, no figures, discussion and acknowledgements adde

Holography of Gravitational Action Functionals

Einstein-Hilbert (EH) action can be separated into a bulk and a surface term, with a specific ("holographic") relationship between the two, so that either can be used to extract information about the other. The surface term can also be interpreted as the entropy of the horizon in a wide class of spacetimes. Since EH action is likely to just the first term in the derivative expansion of an effective theory, it is interesting to ask whether these features continue to hold for more general gravitational actions. We provide a comprehensive analysis of lagrangians of the form L=Q_a^{bcd}R^a_{bcd}, in which Q_a^{bcd} is a tensor with the symmetries of the curvature tensor, made from metric and curvature tensor and satisfies the condition \nabla_cQ^{abcd}=0, and show that they share these features. The Lanczos-Lovelock lagrangians are a subset of these in which Q^{abcd} is a homogeneous function of the curvature tensor. They are all holographic, in a specific sense of the term, and -- in all these cases -- the surface term can be interpreted as the horizon entropy. The thermodynamics route to gravity, in which the field equations are interpreted as TdS=dE+pdV, seems to have greater degree of validity than the field equations of Einstein gravity itself. The results suggest that the holographic feature of EH action could also serve as a new symmetry principle in constraining the semiclassical corrections to Einstein gravity. The implications are discussed.Comment: revtex 4; 17 pages; no figure

Spatially Resolved Patchy Lyman-α\alpha Emission Within the Central Kiloparsec of a Strongly Lensed Quasar Host Galaxy at z = 2.8

We report the detection of extended Lyman-$\alpha$ emission from the host galaxy of SDSS~J2222+2745, a strongly lensed quasar at $z = 2.8$. Spectroscopic follow-up clearly reveals extended Lyman-$\alpha$ in emission between two images of the central active galactic nucleus (AGN). We reconstruct the lensed quasar host galaxy in the source plane by applying a strong lens model to HST imaging, and resolve spatial scales as small as $\sim$200 parsecs. In the source plane we recover the host galaxy morphology to within a few hundred parsecs of the central AGN, and map the extended Lyman-$\alpha$ emission to its physical origin on one side of the host galaxy at radii $\sim$0.5-2 kpc from the central AGN. There are clear morphological differences between the Lyman-$\alpha$ and rest-frame ultraviolet stellar continuum emission from the quasar host galaxy. Furthermore, the relative velocity profiles of quasar Lyman-$\alpha$, host galaxy Lyman-$\alpha$, and metal lines in outflowing gas reveal differences in the absorbing material affecting the AGN and host galaxy. These data indicate the presence of patchy local intervening gas in front of the central quasar and its host galaxy. This interpretation is consistent with the central luminous quasar being obscured across a substantial fraction of its surrounding solid angle, resulting in strong anisotropy in the exposure of the host galaxy to ionizing radiation from the AGN. This work demonstrates the power of strong lensing-assisted studies to probe spatial scales that are currently inaccessible by other means.Comment: Accepted to ApJ Letters; 7 pages, 5 figure

New possibilities arise for studies of hybridization: SNP-based markers for the multi-species Daphnia longispina complex derived from transcriptome data

In order to trace community dynamics and reticulate evolution in hybrid species complexes, long-term comparative studies of natural populations are necessary. Such studies require the development of tools for fine-scale genetic analyses. In the present study, we developed species-diagnostic SNP-based markers for hybridizing freshwater crustaceans: the multispecies Daphnia longispina complex. Specifically, we took advantage of transcriptome data from a key species of this hybrid complex, the annotated genome of a related Daphnia species and well-defined reference genotypes from three parental species. Altogether eleven nuclear loci with several species-specific SNP sites were identified in sequence alignments of these reference genotypes from three parental species and their interspecific hybrids. A PCR-RFLP assay was developed for cost-efficient large population screening by SNP-based genotyping. Taxon assignment by RFLP patterns was nearly perfectly concordant with microsatellite genotyping across several screened populations from Europe. Finally, we were able to amplify two short regions of these loci in formaldehyde-preserved samples dating back to the year 1960. The species-specific SNP-based markers developed here provide valuable tools to study hybridization over time, including the long-term impact of various environmental factors on hybridization and biodiversity changes. SNP-based genotyping will finally allow eco-evolutionary dynamics to be revealed at different time scale

Conclusions from CDF Results on CP Violation in D^0 \to \pi^+\pi^-, K^+K^- and Future Tasks

Within the Standard Model (SM) one predicts both direct and indirect CP violation in D^0 \to \pi^+\pi^-, K^+K^- transitions, although the effects are tiny: Indirect CP asymmetry cannot exceed O(10^{-4}), probably even O(10^{-5}); direct effects are estimated at not larger than 10^{-4}. At B factories direct and indirect asymmetries have been studied with /\tau_{D^0} ~ 1; no CP asymmetry was found with an upper bound of about 1%. CDF has shown intriguing data on CP violation in D^0 \to \pi^+\pi^- [K^+K^-] with /\tau_{D^0} ~ 2.4 [2.65]. Also, CDF has not seen any CP violation. For direct CP asymmetry, CDF has a sensitivity similar to the combination of the B factories, yet for indirect CP violation it yields a significantly smaller sensitivity of a_{cp}^{ind}=(-0.01 +- 0.06_{stat} +- 0.05_{syst})% due to it being based on longer decay times. New Physics models (NP) like Little Higgs Models with T-Parity (LHT) can produce an indirect CP asymmetry up to 1%; CDF's findings thus cover the upper range of realistic NP predictions ~ 0.1 - 1%. One hopes that LHCb and a Super-Flavour Factory will probe the lower range down to ~0.01%. Such non-ad-hoc NP like LHT cannot enhance direct CP violation significantly over the SM level in D^0 \to \pi^+\pi^-, K^+K^- and D^{\pm} \to \pi^{\pm}K^+K^- transitions, but others might well do so.Comment: 11 pages, 1 figure. V2 has minor corrections and corresponds to the published versio

Vibrations of a chain of Xe atoms in a groove of carbon nanotube bundle

We present a lattice dynamics study of the vibrations of a linear chain of Xe adsorbates in groove positions of a bundle of carbon nanotubes. The characteristic phonon frequencies are calculated and the adsorbate polarization vectors discussed. Comparison of the present results with the ones previously published shows that the adsorbate vibrations cannot be treated as completely decoupled from the vibrations of carbon nanotubes and that a significant hybridization between the adsorbate and the tube modes occurs for phonons of large wavelengths.Comment: 3 PS figure

Using experimental evolution to evaluate diversification of Pseudomonas fluorescens SBW25 in complex environments

Understanding the ecological conditions promoting diversification of lineages has been one of the major challenges in the field of evolutionary ecology. The ecological theory of adaptive radiation identified two potential conditions to divergence; selection resulting from differences between environments and from the interaction between species. So far, the best explained factor is differences between environmental features giving rise to divergence of lineages. Most of the other cases on adaptive radiation indicated that resource competition is an important process underlying diversification, although the roles of the other species interactions are not explicitly tested. Predation, for instance, is still underexplored, despite having both ecological and evolutionary impacts on prey populations. Role of predation on diversification remained unsettled, as field studies are challenging and experimental studies showed its modifying effect when selection is driven by resource competition. Importantly, the interacting effects of different ecological processes on diversification should be evaluated in detail. The aim of this thesis is to evaluate the importance of predation, and its effect on diversification when predation and resource competition are both present.  Eine der fundamentalen Fragen der Evolutionsökologie untersucht die Rolle ökologischer Bedingungen bei der Aufspaltung von Arten. Die Theorie der adaptiven Radiation benennt zwei mögliche Szenarien für diese Divergenz: Selektionsprozesse basierend auf der Interaktion zwischen den Arten sowie durch unterschiedliche Umweltbedingungen. Unterschiedliche Umweltbedingungen, die zur Artbildung führen sind bisher am besten erforscht. Die meisten anderen Szenarien adaptiver Radiation postulieren Ressourcenknappheit als weitere Hauptursache, die zur Aufsplittung von Arten führt, auch wenn die Rolle der Interaktionen zwischen den Arten bisher nicht explizit untersucht wurde. So ist beispielsweise ist die Rolle des Räuberverhalten trotz ihres großen ökologischen Einflusses auf Beutepopulationen in diesem Kontext weitestgehend unerforscht. Feldstudien zur Bedeutung von Räuber-Beute-Beziehung im Artbilungsprozess sind sehr schwierig durchzuführen, experimentelle Untersuchungen weisen auf darauf hin, dass der divergierende Einfluss primär dann zum tragen kommt, wenn Selektion durch Ressourcenknappheit getrieben wird. Besonders wichtig ist hierbei die Bedeutung möglicher Interaktionen verschiedener Selektionsprozesse im Detail zu analysieren. Das Ziel der hier vorliegenden Doktorarbeit ist es die Bedeutung von Räuber-Beute-Verhalten und seiner Bedeutung auf Artbildungsprozesse im Kontext von Ressourcenknappheit zu erforschen