1,084 research outputs found
Casimir dependence of transverse distribution of pairs produced from a strong constant chromo-electric background field
The transverse distribution of gluon and quark-antiquark pairs produced from
a strong constant chromo-electric field depends on two gauge invariant
quantities, and , as shown earlier in
[G.C. Nayak and P. van Nieuwenhuizen, Phys. Rev. D 71, 125001 (2005)] for
gluons and in [G.C. Nayak, Phys. Rev. D 72, 125010 (2005)] for quarks. Here, we
discuss the explicit dependence of the distribution on the second Casimir
invariant, C_2, and show the dependence is at most a 15% effect.Comment: 5 fig
New relations between spinor and scalar one-loop effective Lagrangians in constant background fields
Simple new relations are presented between the one-loop effective Lagrangians
of spinor and scalar particles in constant curvature background fields, both
electromagentic and gravitational. These relations go beyond the well-known
cases for self-dual background fields
Quantum Electro and Chromodynamics treated by Thompson's heuristic approach
In this work we apply Thompson's method (of the dimensions and scales) to
study some features of the Quantum Electro and Chromodynamics. This heuristic
method can be considered as a simple and alternative way to the Renormalisation
Group (R.G.) approach and when applied to QED-lagrangian is able to obtain in a
first approximation both the running coupling constant behavior of alpha(mu)
and the mass m(mu).The calculations are evaluated just at d_c=4, where d_c is
the upper critical dimension of the problem, so that we obtain the logarithmic
behavior both for the coupling alpha and the excess of mass Delta m on the
energy scale mu. Although our results are well-known in the vast literature of
field theories,it seems that one of the advantages of Thompson's method, beyond
its simplicity is that it is able to extract directly from QED-lagrangian the
physical (finite) behavior of alpha(mu) and m(mu), bypassing hard problems of
divergences which normally appear in the conventional renormalisation schemes
applied to field theories like QED. Quantum Chromodynamics (QCD) is also
treated by the present method in order to obtain the quark condensate value.
Besides this, the method is also able to evaluate the vacuum pressure at the
boundary of the nucleon. This is done by assumming a step function behavior for
the running coupling constant of the QCD, which fits nicely to some quantities
related to the strong interaction evaluated through the MIT-bag model.Comment: RevTex, 25 pages, no figure
Slowly decaying classical fields, unitarity, and gauge invariance
In classical external gauge fields that fall off less fast than the inverse
of the evolution parameter (time) of the system the implementability of a
unitary perturbative scattering operator (-matrix) is not guaranteed,
although the field goes to zero. The importance of this point is exposed for
the counter-example of low-dimensionally expanding systems. The issues of gauge
invariance and of the interpretation of the evolution at intermediate times are
also intricately linked to that point.Comment: 8 pages, no figure
Observability of an induced electric dipole moment of the neutron from nonlinear QED
It has been shown recently that a neutron placed in an external quasistatic
electric field develops an induced electric dipole moment
due to quantum fluctuations in the QED vacuum. A
feasible experiment which could detect such an effect is proposed and described
here. It is shown that the peculiar angular dependence of
on the orientation of the neutron spin leads to a
characteristic asymmetry in polarized neutron scattering by heavy nuclei. This
asymmetry can be of the order of for neutrons with epithermal
energies. For thermalized neutrons from a hot moderator one still expects
experimentally accessible values of the order of . The contribution of
the induced effect to the neutron scattering length is expected to be only one
order of magnitude smaller than that due to the neutron polarizability from its
quark substructure. The experimental observation of this scattering asymmetry
would be the first ever signal of nonlinearity in electrodynamics due to
quantum fluctuations in the QED vacuum
Unconventional density wave in CeCoIn_5?
Very recently large Nernst effect and Seebeck effect were observed above the
superconducting transition temperature 2.3K in a heavy fermion superconductor
CeCoIn_5. We shall interpret this large Nernst effect in terms of
unconventional density wave (UDW), which appears around T=18K. Also the
temperature dependence of the Seebeck coefficient below T=18K is described in
terms of UDW. Another hallmark for UDW is the angular dependent
magnetoresistance, which should be readily accessible experimentally.Comment: 4 pages, 7 figure
Influence of radiative damping on the optical-frequency susceptibility
Motivated by recent discussions concerning the manner in which damping
appears in the electric polarizability, we show that (a) there is a dependence
of the nonresonant contribution on the damping and that (b) the damping enters
according to the "opposite sign prescription." We also discuss the related
question of how the damping rates in the polarizability are related to
energy-level decay rates
QED vacuum fluctuations and induced electric dipole moment of the neutron
Quantum fluctuations in the QED vacuum generate non-linear effects, such as
peculiar induced electromagnetic fields. In particular, we show here that an
electrically neutral particle, possessing a magnetic dipole moment, develops an
induced electric dipole-type moment with unusual angular dependence, when
immersed in a quasistatic, constant external electric field. The calculation of
this effect is done in the framework of the Euler-Heisenberg effective QED
Lagrangian, corresponding to the weak field asymptotic expansion of the
effective action to one-loop order. It is argued that the neutron might be a
good candidate to probe this signal of non-linearity in QED.Comment: A misprint has been corrected, and three new references have been
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