467 research outputs found
Dynamical Chiral Symmetry Breaking in QED in a Magnetic Field: Toward Exact Results
We describe a (first, to the best of our knowledge) essentially soluble
example of dynamical symmetry breaking phenomenon in a 3+1 dimensional gauge
theory without fundamental scalar fields: QED in a constant magnetic field.Comment: 4 pages, 1 figure, REVTeX. Final version accepted for publication in
Physical Review Letter
Analytic structure of scalar composites in the symmetric phase of the gauged Nambu-Jona-Lasinio model
The gauged Nambu-Jona-Lasinio model in the quenched-ladder approximation has
non-trivial dynamics near a critical scaling region (critical curve) separating
a chiral symmetric and a dynamically chiral symmetry broken phase. Scalar and
pseudoscalar composites corresponding to the four-fermion interaction become
relevant degrees of freedom at short distances, which is reflected in the
appearance of a large anomalous dimension of the four-fermion operators. A
method is introduced for solving the Schwinger-Dyson equation for the Yukawa
vertex in specific kinematic regimes. This allows one to derive an analytic
expression for the scalar propagator, which is valid along the entire critical
curve. The mass and width of the scalar composites in the critical scaling
region are reexamined and the conformal phase transition at the critical gauge
coupling is discussed.Comment: final version to appear in Phys. Rev.
Thermal conductivity and competing orders in d-wave superconductors
We derive the expression for the thermal conductivity \kappa in the
low-temperature limit T \to 0 in d-wave superconductors, taking into account
the presence of competing orders such as spin-density wave, is-pairing, etc..
The expression is used for analyzing recent experimental data in
La_{2-x}Sr_xCuO_4. Our analysis strongly suggests that competing orders can be
responsible for anomalies in behavior of thermal conductivity observed in those
experiments.Comment: revtex4,6 pages,title changed,references and two eps figures
added,text essentially extended,to appear in EPJ
Carlson-Goldman modes in the color superconducting phase of dense QCD
We predict the existence of the gapless Carlson-Goldman modes in the
color-flavor locked color superconducting phase of dense QCD. These modes
resemble Nambu-Goldstone modes of the superconducting phase below the critical
temperature where the Anderson-Higgs mechanism takes place. These modes exist
in the broken phase in the vicinity of the critical line. Their presence does
not eliminate the Meissner effect. The effect of Landau damping on the width of
the Carlson-Goldman modes is discussed.Comment: 5 pages, 2 figures. A few new formulas and references are added, some
numerical errors are corrected, and Fig. 1 is replaced by a new one. To
appear in Phys. Rev.
A Light Dilaton in Walking Gauge Theories
We analyze the existence of a dilaton in gauge theories with approximate
infrared conformal symmetry. To the extent that these theories are governed in
the infrared by an approximate fixed point (walking), the explicit breaking of
the conformal symmetry at these scales is vanishingly small. If confinement and
spontaneous chiral-symmetry breaking set in at some infrared scale, the
resultant breaking of the approximate conformal symmetry can lead to the
existence of a dilaton with mass parametrically small compared to the
confinement scale, and potentially observable at the LHC.Comment: 5 pages, references added, final version in PR
Large N dynamics in QED in a magnetic field
The expression for the dynamical mass of fermions in QED in a magnetic field
is obtained for a large number of the fermion flavor N in the framework of 1/N
expansion. The existence of a threshold value N_{thr}, dividing the theories
with essentially different dynamics, is established. For the number of flavors
N << N_{thr}, the dynamical mass is very sensitive to the value of the coupling
constant \alpha_b, related to the magnetic scale \mu = |eB|. For N of order
N_{thr} or larger, a dynamics similar to that in the Nambu-Jona-Lasinio model
with cutoff of order |eB| and the dimensional coupling constant G \sim
1/(N|eB|) takes place. In this case, the value of the dynamical mass is
essentially \alpha_b independent (the dynamics with an infrared stable fixed
point). The value of N_{thr} separates a weak coupling dynamics (with
\tilde{\alpha}_b \equiv N\alpha_b << 1) from a strong coupling one (with
\tilde{\alpha}_b \gtrsim 1) and is of order 1/\alpha_b.Comment: 4 pages, REVTe
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