17,871 research outputs found
Temperature Dependence of Gluon and Quark Condensates as from Linear Confinement
The gluon and quark condensates and their temperature dependence are
investigated within QCD premises. The input for the former is a gauge invariant
kernel made up of the direct (D), exchange (X) and contact(C) QCD
interactions in the lowest order, but with the perturbative propagator
replaced by a `non-perturbative form obtained via two
differentiations: , ( a scale
parameter), and then setting , to simulate linear confinement. Similarly
for the input kernel the gluon propagator is replaced by the above
form. With these `linear' simulations, the respective condensates are
obtained by `looping' up the gluon and quark lines in the standard manner.
Using Dimensional regularization (DR), the necessary integrals yield the
condensates plus temperature corrections, with a common scale parameter
for both. For gluons the exact result is . Evaluation
of the quark condensate is preceded by an approximate solution of the SDE for
the mass function , giving a recursive formula, with convergence achieved
at the third iteration. Setting the scale parameter equal to the
universal Regge slope , the gluon and quark condensates at T=0 are
found to be and respectively, in fair accord
with QCD sum rule values. Next, the temperature corrections (of order
for both condensates) is determined via finite-temperature field theory a la
Matsubara. Keywords: Gluon Condensate, mass tensor, gauge invariance, linear
confinement, finite-temperature, contour-closing. PACS: 11.15.Tk ; 12.38.Lg ;
13.20.CzComment: 13 pages (LaTeX) including 2 figure
Edge and bulk merons in double quantum dots with spontaneous interlayer phase coherence
We have investigated nucleation of merons in double quantum dots when a
lateral distortion with a reflection symmetry is present in the confinement
potential. We find that merons can nucleate both inside and at the edge of the
dots. In addition to these merons, our results show that electron density
modulations can be also present inside the dots. An edge meron appears to have
approximately a half integer winding number.Comment: 5 pages, 4 figures, Proceedings of 17th International Conference on
High Magnetic Fields in Semiconductor Physic
Hole maximum density droplets of an antidot in strong magnetic fields
We investigate a quantum antidot in the integer quantum Hall regime (the
filling factor is two) by using a Hartree-Fock approach and by transforming the
electron antidot into a system which confines holes via an electron-hole
transformation. We find that its ground state is the maximum density droplet of
holes in certain parameter ranges. The competition between electron-electron
interactions and the confinement potential governs the properties of the hole
droplet such as its spin configuration. The ground-state transitions between
the droplets with different spin configurations occur as magnetic field varies.
For a bell-shape antidot containing about 300 holes, the features of the
transitions are in good agreement with the predictions of a recently proposed
capacitive interaction model for antidots as well as recent experimental
observations. We show this agreement by obtaining the parameters of the
capacitive interaction model from the Hartree-Fock results. An inverse
parabolic antidot is also studied. Its ground-state transitions, however,
display different magnetic-field dependence from that of a bell-shape antidot.
Our study demonstrates that the shape of antidot potential affects its physical
properties significantly.Comment: 12 pages, 11 figure
Single electron control in n-type semiconductor quantum dots using non-Abelian holonomies generated by spin orbit coupling
We propose that n-type semiconductor quantum dots with the Rashba and
Dresselhaus spin orbit interactions may be used for single electron
manipulation through adiabatic transformations between degenerate states. All
the energy levels are discrete in quantum dots and possess a double degeneracy
due to time reversal symmetryin the presence of the Rashba and/or Dresselhaus
spin orbit coupling terms. We find that the presence of double degeneracy does
not necessarily give rise to a finite non-Abelian (matrix) Berry phase. We show
that a distorted two-dimensional harmonic potential may give rise to
non-Abelian Berry phases. The presence of the non-Abelian Berry phase may be
tested experimentally by measuring the optical dipole transitions.Comment: accepted in Phys. Rev.
Unified Analysis of Cosmological Perturbations in Generalized Gravity
In a class of generalized Einstein's gravity theories we derive the equations
and general asymptotic solutions describing the evolution of the perturbed
universe in unified forms. Our gravity theory considers general couplings
between the scalar field and the scalar curvature in the Lagrangian, thus
includes broad classes of generalized gravity theories resulting from recent
attempts for the unification. We analyze both the scalar-type mode and the
gravitational wave in analogous ways. For both modes the large scale evolutions
are characterized by the same conserved quantities which are valid in the
Einstein's gravity. This unified and simple treatment is possible due to our
proper choice of the gauges, or equivalently gauge invariant combinations.Comment: 4 pages, revtex, no figure
The Fate of the Accelerating Universe
The presently accelerating universe may keep accelerating forever, eventually
run into the event horizon problem, and thus be in conflict with the
superstring idea. In the other way around, the current accelerating phase as
well as the fate of the universe may be swayed by a negative cosmological
constant, which dictates a big crunch. Based on the current observational data,
in this paper we investigate how large the magnitude of a negative cosmological
constant is allowed to be. In addition, for distinguishing the sign of the
cosmological constant via observations, we point out that a measure of the
evolution of the dark energy equation of state may be a good discriminator.
Hopefully future observations will provide much more detailed information about
dark energy and thereby indicates the sign of the cosmological constant as well
as the fate of the presently accelerating universe.Comment: 16 pages, 5 figures, LaTe
Optimal Quantum State Estimation with Use of the No-Signaling Principle
A simple derivation of the optimal state estimation of a quantum bit was
obtained by using the no-signaling principle. In particular, the no-signaling
principle determines a unique form of the guessing probability independently of
figures of merit, such as the fidelity or information gain. This proves that
the optimal estimation for a quantum bit can be achieved by the same
measurement for almost all figures of merit.Comment: 3 pages, 1 figur
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