472 research outputs found
Techni-dilaton at Conformal Edge
Techni-dilaton (TD) was proposed long ago in the technicolor (TC) near
criticality/conformality. To reveal the critical behavior of TD, we explicitly
compute the nonperturbative contributions to the scale anomaly
, which
are generated by the dynamical mass m of the techni-fermions. Our computation
is based on the (improved) ladder Schwinger-Dyson equation, with the gauge
coupling replaced by the two-loop running one having the
Caswell-Banks-Zaks IR fixed point : for the IR region , where is
the intrinsic scale (analogue of of QCD) relevant to the
perturbative scale anomaly. We find that
and in the
criticality limit () ("conformal edge"). Our result precisely
reproduces the formal identity , where is the nonperturbative beta function
corresponding to the above essential singularity scaling of .
Accordingly, the PCDC implies at criticality limit, where is the mass of TD and
the decay constant of TD. We thus conclude that at criticality limit
the TD could become a "true (massless) Nambu-Goldstone boson" ,
only when , namely getting decoupled, as was the case of
"holographic TD" of Haba-Matsuzaki-Yamawaki. The decoupled TD can be a
candidate of dark matter.Comment: 17 pages, 14 figures; discussions clarified, references added, to
appear in Phys.Rev.
Dynamics of QCD in a Strong Magnetic Field
QCD in a strong magnetic field yields an example of a rich, sophisticated and
controllable dynamics.Comment: 12 pages, 1 figure, Latex, Talk at Symposium and Workshop "Continuous
Advances in QCD 2002/Arkadyfest, May 17-23, 200
Toward theory of quantum Hall effect in graphene
We analyze a gap equation for the propagator of Dirac quasiparticles and
conclude that in graphene in a magnetic field, the order parameters connected
with the quantum Hall ferromagnetism dynamics and those connected with the
magnetic catalysis dynamics necessarily coexist (the latter have the form of
Dirac masses and correspond to excitonic condensates). This feature of graphene
could lead to important consequences, in particular, for the existence of
gapless edge states. Solutions of the gap equation corresponding to recently
experimentally discovered novel plateaus in graphene in strong magnetic fields
are described.Comment: 5 pages, no figures, v.2: to match published versio
A study of Schwinger-Dyson Equations for Yukawa and Wess-Zumino Models
We study Schwinger-Dyson equation for fermions in Yukawa and Wess-Zumino
models, in terms of dynamical mass generation and the wavefunction
renormalization function. In the Yukawa model with -type interaction
between scalars and fermions, we find a critical coupling in the quenched
approximation above which fermions acquire dynamical mass. This is shown to be
true beyond the bare 3-point vertex approximation. In the Wess-Zumino model,
there is a neat cancellation of terms leading to no dynamical mass for
fermions. We comment on the conditions under which these results are general
beyond the rainbow approximation and also on the ones under which supersymmetry
is preserved and the scalars as well do not acquire mass. The results are in
accordance with the non-renormalization theorem at least to order in
perturbation theory. In both the models, we also evaluate the wavefunction
renormalization function, analytically in the neighbourhood of the critical
coupling and numerically, away from it.Comment: 12 pages and 7 Postscript figures, accepted for publication in
Journal of Physics G: Nuclear and Particle Physic
Dynamical mechanism for ultra-light scalar Dark Matter
Assuming a double-well bare potential for a self-interacting scalar field,
with the Higgs vacuum expectation value, it is shown that non-perturbative
quantum corrections naturally lead to ultra-light particles of mass
eV, if these non-perturbative effects occur at a time
consistent with the Electroweak phase transition. This mechanism could be
relevant in the context of Bose Einstein Condensate studies for the description
of cold Dark Matter. Given the numerical consistency with the Electroweak
transition, an interaction potential for Higgs and Dark Matter fields is
proposed, where spontaneous symmetry breaking for the Higgs field leads to the
generation of ultra-light particles, in addition to the usual Higgs mechanism.
This model also naturally leads to extremely weak interactions between the
Higgs and Dark Matter particles.Comment: 12 pages, includes the derivation of the effective potential
suppressed by the volum
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
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