927 research outputs found
Renormalization Group Study of Magnetic Catalysis in the 3d Gross-Neveu Model
Magnetic catalysis describes the enhancement of symmetry breaking quantum
fluctuations in chirally symmetric quantum field theories by the coupling of
fermionic degrees of freedom to a magnetic background configuration. We use the
functional renormalization group to investigate this phenomenon for interacting
Dirac fermions propagating in (2+1)-dimensional spacetime, described by the
Gross-Neveu model. We identify pointlike operators up to quartic fermionic
terms that can be generated in the renormalization group flow by the presence
of an external magnetic field. We employ the beta function for the fermionic
coupling to quantitatively analyze the field dependence of the induced spectral
gap. Within our pointlike truncation, the renormalization group flow provides a
simple picture for magnetic catalysis.Comment: 14 pages, 6 figures, typos correcte
The low temperature corrections to the Casimir force between a sphere and a plane
We calculate the low temperature corrections to the free energy for a sphere
in front of a plane. First, the scalar field obeying Dirichet or Neumann
boundary conditions is considered. Second, the electromagnetic field is
studied, the sphere being perfectly conducting and being a dielectric ball with
both, constant permittivity and permittivity of the plasma model.Comment: Submitted to the proceedings of the Workshop "Cosmology, Quantum
Vacuum and Zeta Functions", Universitat Aut\`onoma de Barcelona, 8-10th
March, 2010; 12 pages, 5 figure
Worldline algorithms for Casimir configurations
We present improved worldline numerical algorithms for high-precision
calculations of Casimir interaction energies induced by scalar-field
fluctuations with Dirichlet boundary conditions for various Casimir geometries.
Significant reduction of numerical cost is gained by exploiting the symmetries
of the worldline ensemble in combination with those of the configurations. This
facilitates high-precision calculations on standard PCs or small clusters. We
illustrate our strategies using the experimentally most relevant sphere-plate
and cylinder-plate configuration. We compute Casimir curvature effects for a
wide parameter range, revealing the tight validity bounds of the commonly used
proximity force approximation (PFA). We conclude that data analysis of future
experiments aiming at a precision of 0.1% must no longer be based on the PFA.
Revisiting the parallel-plate configuration, we find a mapping between the
D-dimensional Casimir energy and properties of a random-chain polymer ensemble.Comment: 23 pages, 9 figure
Tomographic separation of composite spectra. The components of Plaskett's Star
The UV photospheric lines of Plaskett's Star (HD 47129), a 14.4 day period, double lined O-type spectroscopic binary were analyzed. Archival data from IUE (17 spectra well distributed in orbital phase) were analyzed with several techniques. A cross correlation analysis, which showed that the secondary produces significant lines in the UV, indicates that the mass ratio is q = 1.18 + or - 0.12 (secondary slightly more massive). A tomography algorithm was used to produce the separate spectra of the two stars in six spectral regions. The interpolated spectral classifications of the primary and secondary, 07.3 I and 06.2 I, respectively, were estimated through a comparison of UV line ratios with those in spectral standard stars. The intensity ratio of the stars in the UV is 0.53 + or - 0.05 (primary brighter). The secondary lines appear rotationally broadened, and the projected rotational velocity V sin i for this star is estimated to be 310 + or - 20 km/s. The possible evolutionary history of this system is discussed through a comparison of the positions of the components and evolutionary tracks in the H-R diagram
Non-monotonic thermal Casimir force from geometry-temperature interplay
The geometry dependence of Casimir forces is significantly more pronounced in
the presence of thermal fluctuations due to a generic geometry-temperature
interplay. We show that the thermal force for standard sphere-plate or
cylinder-plate geometries develops a non-monotonic behavior already in the
simple case of a fluctuating Dirichlet scalar. In particular, the attractive
thermal force can increase for increasing distances below a critical
temperature. This anomalous behavior is triggered by a reweighting of relevant
fluctuations on the scale of the thermal wavelength. The essence of the
phenomenon becomes transparent within the worldline picture of the Casimir
effect.Comment: 4 pages, 4 figure
Casimir effect for curved geometries: PFA validity limits
We compute Casimir interaction energies for the sphere-plate and
cylinder-plate configuration induced by scalar-field fluctuations with
Dirichlet boundary conditions. Based on a high-precision calculation using
worldline numerics, we quantitatively determine the validity bounds of the
proximity force approximation (PFA) on which the comparison between all
corresponding experiments and theory are based. We observe the quantitative
failure of the PFA on the 1% level for a curvature parameter a/R > 0.00755.
Even qualitatively, the PFA fails to predict reliably the correct sign of
genuine Casimir curvature effects. We conclude that data analysis of future
experiments aiming at a precision of 0.1% must no longer be based on the PFA.Comment: 4 pages, 4 figure
Flow Equation for Supersymmetric Quantum Mechanics
We study supersymmetric quantum mechanics with the functional RG formulated
in terms of an exact and manifestly off-shell supersymmetric flow equation for
the effective action. We solve the flow equation nonperturbatively in a
systematic super-covariant derivative expansion and concentrate on systems with
unbroken supersymmetry. Already at next-to-leading order, the energy of the
first excited state for convex potentials is accurately determined within a 1%
error for a wide range of couplings including deeply nonperturbative regimes.Comment: 24 pages, 8 figures, references added, typos correcte
Determinant Calculations Using Random Walk Worldline Loops
We use statistical ensembles of worldline loops generated by random walk on
hypercubic lattices to calculate matter determinants in background Yang-Mills
fields.Comment: 3 pages, 3 ps figures, Lattice2002 (algor
Light Cone Condition for a Thermalized QED Vacuum
Within the QED effective action approach, we study the propagation of
low-frequency light at finite temperature. Starting from a general effective
Lagrangian for slowly varying fields whose structure is solely dictated by
Lorentz covariance and gauge invariance, we derive the light cone condition for
light propagating in a thermalized QED vacuum. As an application, we calculate
the velocity shifts, i.e., refractive indices of the vacuum, induced by
thermalized fermions to one loop. We investigate various temperature domains
and also include a background magnetic field. While low-temperature effects to
one loop are exponentially damped by the electron mass, there exists a maximum
velocity shift of in the
intermediate-temperature domain .Comment: 9 pages, 3 figures, REVTeX, typos corrected, final version to appear
in Phys. Rev.
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