165 research outputs found
Renormalization-Group Analysis of Layered Sine-Gordon Type Models
We analyze the phase structure and the renormalization group (RG) flow of the
generalized sine-Gordon models with nonvanishing mass terms, using the
Wegner-Houghton RG method in the local potential approximation. Particular
emphasis is laid upon the layered sine-Gordon (LSG) model, which is the
bosonized version of the multi-flavour Schwinger model and approaches the sum
of two ``normal'', massless sine-Gordon (SG) models in the limit of a vanishing
interlayer coupling J. Another model of interest is the massive sine-Gordon
(MSG) model. The leading-order approximation to the UV (ultra-violet) RG flow
predicts two phases for the LSG as well as for the MSG, just as it would be
expected for the SG model, where the two phases are known to be separated by
the Coleman fixed point. The presence of finite mass terms (for the LSG and the
MSG) leads to corrections to the UV RG flow, which are naturally identified as
the ``mass corrections''. The leading-order mass corrections are shown to have
the following consequences: (i) for the MSG model, only one phase persists, and
(ii) for the LSG model, the transition temperature is modified. Within the
mass-corrected UV scaling laws, the limit of J -> 0 is thus nonuniform with
respect to the phase structure of the model. The modified phase structure of
general massive sine-Gordon models is connected with the breaking of symmetries
in the internal space spanned by the field variables. For the LSG, the
second-order subleading mass corrections suggest that there exists a cross-over
regime before the IR scaling sets in, and the nonlinear terms show explicitly
that higher-order Fourier modes appear in the periodic blocked potential.Comment: 27 pages, 7 figure
Effective Action and Phase Structure of Multi-Layer Sine-Gordon Type Models
We analyze the effective action and the phase structure of N-layer
sine-Gordon type models, generalizing the results obtained for the two-layer
sine-Gordon model found in [I. Nandori, S. Nagy, K. Sailer and U. D.
Jentschura, Nucl. Phys. B725, 467-492 (2005)]. Besides the obvious field
theoretical interest, the layered sine-Gordon model has been used to describe
the vortex properties of high transition temperature superconductors, and the
extension of the previous analysis to a general N-layer model is necessary for
a description of the critical behaviour of vortices in realistic multi-layer
systems. The distinction of the Lagrangians in terms of mass eigenvalues is
found to be the decisive parameter with respect to the phase structure of the
N-layer models, with neighbouring layers being coupled by quadratic terms in
the field variables. By a suitable rotation of the field variables, we identify
the periodic modes (without explicit mass terms) in the N-layer structure,
calculate the effective action and determine their Kosterlitz-Thouless type
phase transitions to occur at a coupling parameter \beta^2_{c} = 8 N \pi, where
N is the number of layers (or flavours in terms of the multi-flavour Schwinger
model).Comment: 15 page
Length-scale-dependent phase transition in BSCCO single crystals
Electrical transport measurements using a multiterminal configuration are
presented, which prove that in BSCCO single crystals near the transition
temperature in zero external magnetic field the secondary voltage is induced by
thermally activated vortex loop unbinding. The phase transition between the
bound and unbound states of the vortex loops was found to be below the
temperature where the phase coherence of the superconducting order parameter
extends over the whole volume of the sample. We show experimentally that 3D/2D
phase transition in vortex dimensionality is a length-scale-dependent layer
decoupling process and takes place simultaneously with the 3D/2D phase
transition in superconductivity at the same temperature.Comment: 14 pages, 4 figures, to be published in Philos. Ma
On the renormalization of the bosonized multi-flavor Schwinger model
The phase structure of the bosonized multi-flavor Schwinger model is
investigated by means of the differential renormalization group (RG) method. In
the limit of small fermion mass the linearized RG flow is sufficient to
determine the low-energy behavior of the N-flavor model, if it has been rotated
by a suitable rotation in the internal space. For large fermion mass, the exact
RG flow has been solved numerically. The low-energy behavior of the
multi-flavor model is rather different depending on whether N=1 or N>1, where N
is the number of flavors. For N>1 the reflection symmetry always suffers
breakdown in both the weak and strong coupling regimes, in contrary to the N=1
case, where it remains unbroken in the strong coupling phase.Comment: 13 pages, 2 figures, final version, published in Physics Letters
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