21,339 research outputs found
Simple Current Actions of Cyclic Groups
Permutation actions of simple currents on the primaries of a Rational
Conformal Field Theory are considered in the framework of admissible weighted
permutation actions. The solution of admissibility conditions is presented for
cyclic quadratic groups: an irreducible WPA corresponds to each subgroup of the
quadratic group. As a consequence, the primaries of a RCFT with an order n
integral or half-integral spin simple current may be arranged into multiplets
of length k^2 (where k is a divisor of n) or 3k^2 if the spin of the simple
current is half-integral and k is odd.Comment: Added reference, minor change
Landau levels, response functions and magnetic oscillations from a generalized Onsager relation
A generalized semiclassical quantization condition for cyclotron orbits was
recently proposed by Gao and Niu \cite{Gao}, that goes beyond the Onsager
relation \cite{Onsager}. In addition to the integrated density of states, it
formally involves magnetic response functions of all orders in the magnetic
field. In particular, up to second order, it requires the knowledge of the
spontaneous magnetization and the magnetic susceptibility, as was early
anticipated by Roth \cite{Roth}. We study three applications of this relation
focusing on two-dimensional electrons. First, we obtain magnetic response
functions from Landau levels. Second we obtain Landau levels from response
functions. Third we study magnetic oscillations in metals and propose a proper
way to analyze Landau plots (i.e. the oscillation index as a function of
the inverse magnetic field ) in order to extract quantities such as a
zero-field phase-shift. Whereas the frequency of -oscillations depends on
the zero-field energy spectrum, the zero-field phase-shift depends on the
geometry of the cell-periodic Bloch states via two contributions: the Berry
phase and the average orbital magnetic moment on the Fermi surface. We also
quantify deviations from linearity in Landau plots (i.e. aperiodic magnetic
oscillations), as recently measured in surface states of three-dimensional
topological insulators and emphasized by Wright and McKenzie \cite{Wright}.Comment: 31 pages, 8 figures; v2: SciPost style; v3: several references added,
small corrections, typos fixed; v4: abstract changed, generalized
quantization condition called Roth-Gao-Niu; v5: minor modifications, 2
references adde
Pseudorapidity shape of elliptic flow as signature for fast equilibration in relativistic heavy-ion collisions at energies up to sqrt(s) = 200 GeV
The implications of parton recombination processes on the dynamics of
ultrarelativistic heavy-ion reactions are investigated. To do so, the
quark-gluon string transport model has been extended for partonic recombination
and fusion processes. Parton recombination leads to short equilibration times
and improves significantly on the theoretical description of measured directed
and elliptic flow, i.e., v_1 and v_2, distributions in Au+Au collisions at
sqrt(s) = 200 GeV, in particular what concerns their pseudorapidity dependence.
The shape of v_2(eta) is found to be closely related to fast thermalization.Comment: 7 pages (revtex4) with 4 figures, v3: substantially extended
description and discussion of the model and its results, accepted for
publication in Phys. Rev.
A reason for fusion rules to be even
We show that certain tensor product multiplicities in semisimple braided
sovereign tensor categories must be even. The quantity governing this behavior
is the Frobenius-Schur indicator. The result applies in particular to the
representation categories of large classes of groups, Lie algebras, Hopf
algebras and vertex algebras.Comment: 6 pages, LaTe
Tunable orbital susceptibility in - tight-binding models
We study the importance of interband effects on the orbital susceptibility of
three bands - tight-binding models. The particularity of
these models is that the coupling between the three energy bands (which is
encoded in the wavefunctions properties) can be tuned (by a parameter )
without any modification of the energy spectrum. Using the gauge-invariant
perturbative formalism that we have recently developped, we obtain a generic
formula of the orbital susceptibility of - tight-binding
models. Considering then three characteristic examples that exhibit either
Dirac, semi-Dirac or quadratic band touching, we show that by varying the
parameter and thus the wavefunctions interband couplings, it is
possible to drive a transition from a diamagnetic to a paramagnetic peak of the
orbital susceptibility at the band touching. In the presence of a gap
separating the dispersive bands, we show that the susceptibility inside the gap
exhibits a similar dia to paramagnetic transition.Comment: 15 pages,5 figs. Proceedings of the International Workshop on Dirac
Electrons in Solids 2015Proceedings of the International Workshop on Dirac
Electrons in Solids 201
Non--Newtonian viscosity of interacting Brownian particles: comparison of theory and data
A recent first-principles approach to the non-linear rheology of dense
colloidal suspensions is evaluated and compared to simulation results of
sheared systems close to their glass transitions. The predicted scenario of a
universal transition of the structural dynamics between yielding of glasses and
non-Newtonian (shear-thinning) fluid flow appears well obeyed, and calculations
within simplified models rationalize the data over variations in shear rate and
viscosity of up to 3 decades.Comment: 6 pages, 2 figures; J. Phys. Condens. Matter to be published (Jan.
2003
Upper critical field measurements up to 60 T in arsenic-deficient LaO_(0.9)F_(0.1)FeAs_(1-delta): Pauli limiting behaviour at high fields vs improved superconductivity at low fields
We report resistivity and upper critical field B_c2(T) data for As deficient
LaO_(0.9)F_(0.1)FeAs_(1-delta) in a wide temperature and high field range up to
60 T. These disordered samples exhibit a slightly enhanced superconducting
transition at T_c = 29 K and a significantly enlarged slope dB_(c2))/dT = -5.4
T/K near T_c which contrasts with a flattening of B_(c2)(T) starting near 23 K
above 30 T. This flattening is interpreted as Pauli limiting behaviour (PLB)
with B_(c2)(0) approx 63 T. We compare our results with B_(c2)(T)-data reported
in the literature for clean and disordered samples. Whereas clean samples show
no PLB for fields below 60 to 70 T, the hitherto unexplained flattening of
B_(c2)(T) for applied fields H || ab observed for several disordered closely
related systems is interpreted also as a manifestation of PLB. Consequences of
our results are discussed in terms of disorder effects within the frame of
conventional and unconventional superconductivity.Comment: 4 pages, 3 figures, submitted to RHMF09 (9th International Conference
on the Research in High Magnetic Fields), Dresden, July 22-25, 200
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