272 research outputs found
Critical properties of the N-color London model
The critical properties of -color London model are studied in
dimensions. The model is dualized to a theory of vortex fields interacting
through a Coulomb and a screened potential. The model with N=2 shows two
anomalies in the specific heat. From the critical exponents and ,
the mass of the gauge field, and the vortex correlation functions, we conclude
that one anomaly corresponds to an {\it inverted} \xy fixed point, while the
other corresponds to a \xy fixed point. There are fixed points, namely one
corresponding to an inverted \xy fixed point, and corresponding to
neutral \xy fixed points. This represents a novel type of quantum fluid, where
superfluid modes arise out of charged condensates.Comment: 4 pages, 3 figures, new references added. Accepted for publication in
Physical Review Letter
Compact U(1) gauge theories in 2+1 dimensions and the physics of low dimensional insulating materials
Compact abelian gauge theories in dimensions arise often as an
effective field-theoretic description of models of quantum insulators. In this
paper we review some recent results about the compact abelian Higgs model in
in that context.Comment: 5 pages, 3 figures; based on talk by F.S. Nogueira in the Aachen
HEP2003 conferenc
Phase structure of Abelian Chern-Simons gauge theories
We study the effect of a Chern-Simons (CS) term in the phase structure of two
different Abelian gauge theories. For the compact Maxwell-Chern-Simons theory,
we obtain that for values of the CS coupling with ,
the theory is equivalent to a gas of closed loops with contact interaction,
exhibiting a phase transition in the universality class. We also employ
Monte Carlo simulations to study the noncompact U(1) Abelian Higgs model with a
CS term. Finite size scaling of the third moment of the action yields critical
exponents and that vary continuously with the strength of the CS
term, and a comparison with available analytical results is made.Comment: RevTex4, 4 pages, 1 figure; v3: improvements and corrections made in
the first part of the paper; references added. To be published in Europhysics
Letter
Selection, inheritance, and the evolution of parent-offspring interactions
Very few studies have examined parent-offspring interactions from a quantitative genetic perspective. We used a cross-fostering design and measured genetic correlations and components of social selection arising from two parental and two offspring behaviors in the burying beetle Nicrophorus vespilloides. Genetic correlations were assessed by examining behavior of relatives independent of common social influences. We found positive genetic correlations between all pairs of behaviors, including between parent and offspring behaviors. Patterns of selection were assessed by standardized performance and selection gradients. Parental provisioning had positive effects on offspring performance and fitness, while remaining near the larvae without feeding them had negative effects. Begging had positive effects on offspring performance and fitness, while increased competition among siblings had negative effects. Coadaptations between parenting and offspring behavior appear to be maintained by genetic correlations and functional trade-offs; parents that feed their offspring more also spend more time in the area where they can forage for themselves. Families with high levels of begging have high levels of sibling competition. Integrating information from genetics and selection thus provides a general explanation for why variation persists in seemingly beneficial traits expressed in parent-offspring interactions and illustrates why it is important to measure functionally related suites of behaviors
Observation of a metallic superfluid in a numerical experiment
We report the observation, in Monte Carlo simulations, of a novel type of
quantum ordered state: {\it the metallic superfluid}. The metallic superfluid
features ohmic resistance to counter-flows of protons and electrons, while
featuring dissipationless co-flows of electrons and protons. One of the
candidates for a physical realization of this remarkable state of matter is
hydrogen or its isotopes under high compression. This adds another potential
candidate to the presently known quantum dissipationless states, namely
superconductors, superfluid liquids and vapours, and supersolids.Comment: 4 pages, 2 figures. Accepted for publication in Phys. Rev. Let
Coadaptation of prenatal and postnatal maternal effects
In a wide variety of species, a female's age of first reproduction influences offspring size and survival, suggesting that there exists an optimal timing of reproduction. Mothers in many species also influence offspring size and survival after birth through variation in parental care. We experimentally separated these effects in the burying beetle Nicrophorus vespilloides to test for coadaptation between prenatal and postnatal maternal effects associated with age at first reproduction. Females that reproduced early produced offspring with lower birth weight. The amount of parental care depended on the age of first reproduction of the caretaker, as did the extent of offspring begging. As predicted for a coadaptation of maternal effects, prenatal and postnatal effects were opposite for different-aged mothers, and larval weight gain and survival was greatest when the age of the caretaker and birth mother matched. Thus, prenatal effects intrinsically associated with age of first reproduction can be ameliorated by innate plasticity in postnatal care. A coadaptation of prenatal and postnatal maternal effects may evolve to allow variable timing of the first reproductive attempt. Such a coadaptation might be particularly valuable when females are constrained from reproducing at an optimal age, as, for example, in species that breed on scarce and unpredictable resources
Criticality in the 2+1-dimensional compact Higgs model and fractionalized insulators
We use a novel method of computing the third moment M_3 of the action of the
2+1-dimensional compact Higgs model in the adjoint representation with q=2 to
extract correlation length and specific heat exponents nu and alpha, without
invoking hyperscaling. Finite-size scaling analysis of M_3 yields the ratio
(1+alpha)/nu and 1/nu separately. We find that alpha and nu vary along the
critical line of the theory, which however exhibits a remarkable resilience of
Z_2 criticality. We propose this novel universality class to be that of the
quantum phase transition from a Mott-Hubbard insulator to a
charge-fractionalized insulator in two spatial dimensions.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
A superconductor to superfluid phase transition in liquid metallic hydrogen
Although hydrogen is the simplest of atoms, it does not form the simplest of
solids or liquids. Quantum effects in these phases are considerable (a
consequence of the light proton mass) and they have a demonstrable and often
puzzling influence on many physical properties, including spatial order. To
date, the structure of dense hydrogen remains experimentally elusive. Recent
studies of the melting curve of hydrogen indicate that at high (but
experimentally accessible) pressures, compressed hydrogen will adopt a liquid
state, even at low temperatures. In reaching this phase, hydrogen is also
projected to pass through an insulator-to-metal transition. This raises the
possibility of new state of matter: a near ground-state liquid metal, and its
ordered states in the quantum domain. Ordered quantum fluids are traditionally
categorized as superconductors or superfluids; these respective systems feature
dissipationless electrical currents or mass flow. Here we report an analysis
based on topological arguments of the projected phase of liquid metallic
hydrogen, finding that it may represent a new type of ordered quantum fluid.
Specifically, we show that liquid metallic hydrogen cannot be categorized
exclusively as a superconductor or superfluid. We predict that, in the presence
of a magnetic field, liquid metallic hydrogen will exhibit several phase
transitions to ordered states, ranging from superconductors to superfluids.Comment: for a related paper see cond-mat/0410425. A correction to the front
page caption appeared in Oct 14 issue of Nature:
http://www.nature.com/nature/links/041014/041014-11.htm
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