1,007,374 research outputs found
A realization of the Lie algebra associated to a Kantor triple system
We present a nonlinear realization of the 5-graded Lie algebra associated to
a Kantor triple system. Any simple Lie algebra can be realized in this way,
starting from an arbitrary 5-grading. In particular, we get a unified
realization of the exceptional Lie algebras f_4, e_6, e_7, e_8, in which they
are respectively related to the division algebras R, C, H, O.Comment: 11 page
On structure of effective action in four-dimensional quantum dilaton supergravity
A general structure of effective action in new chiral superfield model
associated with , supergravity is investigated. This model
corresponds to finite quantum field theory and does not demand the
regularization and renormalization at effective action calculation. It is shown
that in local approximation the effective action is defined by two objects
called general superfield effective lagrangian and chiral superfield effective
lagrangian. A proper-time method is generalized for calculation of these two
effective lagrangians in superfield manner. Power expansion of the effective
action in supercovariant derivatives is formulated and the lower terms of such
an expansion are calculated in explicit superfield form
Effect of the Spatial Dispersion on the Shape of a Light Pulse in a Quantum Well
Reflectance, transmittance and absorbance of a symmetric light pulse, the
carrying frequency of which is close to the frequency of interband transitions
in a quantum well, are calculated. Energy levels of the quantum well are
assumed discrete, and two closely located excited levels are taken into
account. A wide quantum well (the width of which is comparable to the length of
the light wave, corresponding to the pulse carrying frequency) is considered,
and the dependance of the interband matrix element of the momentum operator on
the light wave vector is taken into account. Refractive indices of barriers and
quantum well are assumed equal each other. The problem is solved for an
arbitrary ratio of radiative and nonradiative lifetimes of electronic
excitations. It is shown that the spatial dispersion essentially affects the
shapes of reflected and transmitted pulses. The largest changes occur when the
radiative broadening is close to the difference of frequencies of interband
transitions taken into account.Comment: 7 pages, 5 figure
Back reaction of vacuum and the renormalization group flow from the conformal fixed point
We consider the GUT-like model with two scalar fields which has infinitesimal
deviation from the conformal invariant fixed point at high energy region. In
this case the dominating quantum effect is the conformal trace anomaly and the
interaction between the anomaly-generated propagating conformal factor of the
metric and the usual dimensional scalar field. This interaction leads to the
renormalization group flow from the conformal point. In the supersymmetric
conformal invariant model such an effect produces a very weak violation of
sypersymmetry at lower energies.Comment: 15 pages, LaTex, ten figures, uuencoded fil
Instability of coherent states of a real scalar field
We investigate stability of both localized time-periodic coherent states
(pulsons) and uniformly distributed coherent states (oscillating condensate) of
a real scalar field satisfying the Klein-Gordon equation with a logarithmic
nonlinearity. The linear analysis of time-dependent parts of perturbations
leads to the Hill equation with a singular coefficient. To evaluate the
characteristic exponent we extend the Lindemann-Stieltjes method, usually
applied to the Mathieu and Lame equations, to the case that the periodic
coefficient in the general Hill equation is an unbounded function of time. As a
result, we derive the formula for the characteristic exponent and calculate the
stability-instability chart. Then we analyze the spatial structure of the
perturbations. Using these results we show that the pulsons of any amplitudes,
remaining well-localized objects, lose their coherence with time. This means
that, strictly speaking, all pulsons of the model considered are unstable.
Nevertheless, for the nodeless pulsons the rate of the coherence breaking in
narrow ranges of amplitudes is found to be very small, so that such pulsons can
be long-lived. Further, we use the obtaned stability-instability chart to
examine the Affleck-Dine type condensate. We conclude the oscillating
condensate can decay into an ensemble of the nodeless pulsons.Comment: 11 pages, 8 figures, submitted to Physical Review
Coulomb Blockade Peak Spacings: Interplay of Spin and Dot-Lead Coupling
For Coulomb blockade peaks in the linear conductance of a quantum dot, we
study the correction to the spacing between the peaks due to dot-lead coupling.
This coupling can affect measurements in which Coulomb blockade phenomena are
used as a tool to probe the energy level structure of quantum dots. The
electron-electron interactions in the quantum dot are described by the constant
exchange and interaction (CEI) model while the single-particle properties are
described by random matrix theory. We find analytic expressions for both the
average and rms mesoscopic fluctuation of the correction. For a realistic value
of the exchange interaction constant J_s, the ensemble average correction to
the peak spacing is two to three times smaller than that at J_s = 0. As a
function of J_s, the average correction to the peak spacing for an even valley
decreases monotonically, nonetheless staying positive. The rms fluctuation is
of the same order as the average and weakly depends on J_s. For a small
fraction of quantum dots in the ensemble, therefore, the correction to the peak
spacing for the even valley is negative. The correction to the spacing in the
odd valleys is opposite in sign to that in the even valleys and equal in
magnitude. These results are robust with respect to the choice of the random
matrix ensemble or change in parameters such as charging energy, mean level
spacing, or temperature.Comment: RevTex, 11 pages, 9 figures. v2: Conclusions section expanded.
Accepted for publication in PR
A Four-Dimensional Theory for Quantum Gravity with Conformal and Nonconformal Explicit Solutions
The most general version of a renormalizable theory corresponding to a
dimensionless higher-derivative scalar field model in curved spacetime is
explored. The classical action of the theory contains independent
functions, which are the generalized coupling constants of the theory. We
calculate the one-loop beta functions and then consider the conditions for
finiteness. The set of exact solutions of power type is proven to consist of
precisely three conformal and three nonconformal solutions, given by remarkably
simple (albeit nontrivial) functions that we obtain explicitly. The finiteness
of the conformal theory indicates the absence of a conformal anomaly in the
finite sector. The stability of the finite solutions is investigated and the
possibility of renormalization group flows is discussed as well as several
physical applications.Comment: LaTeX, 18 pages, no figure
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