1,963 research outputs found
Bit error rate testing of a proof-of-concept model baseband processor
Bit-error-rate tests were performed on a proof-of-concept baseband processor. The BBP, which operates at an intermediate frequency in the C-Band, demodulates, demultiplexes, routes, remultiplexes, and remodulates digital message segments received from one ground station for retransmission to another. Test methods are discussed and test results are compared with the Contractor's test results
Lattice supersymmetry
A method is proposed for latticizing a class of supersymmetric gauge
theories, including N=4 super Yang-Mills. The technique is inspired by recent
work on ``deconstruction''. Part of the target theory's supersymmetry is
realized exactly on the lattice, reducing or eliminating the need for fine
tuning. (Talk based on the paper "Supersymmetry on a Spatial Lattice",
hep-lat/0206019, by D.B.K., Emmanuel Katz and Mithat Unsal).Comment: Lattice2002(higgssusy), 3 pages, no figure
Temperature in Fermion Systems and the Chiral Fermion Determinant
We give an interpretation to the issue of the chiral determinant in the
heat-kernel approach. The extra dimension (5-th dimension) is interpreted as
(inverse) temperature. The 1+4 dim Dirac equation is naturally derived by the
Wick rotation for the temperature. In order to define a ``good'' temperature,
we choose those solutions of the Dirac equation which propagate in a fixed
direction in the extra coordinate. This choice fixes the regularization of the
fermion determinant. The 1+4 dimensional Dirac mass () is naturally
introduced and the relation: 4 dim electron momentum
ultraviolet cut-off, naturally appears. The chiral anomaly is explicitly
derived for the 2 dim Abelian model. Typically two different regularizations
appear depending on the choice of propagators. One corresponds to the chiral
theory, the other to the non-chiral (hermitian) theory.Comment: 24 pages, some figures, to be published in Phys.Rev.
Half-Life of O
We have measured the half-life of O, a superallowed decay isotope. The O was produced by the
C(He,n)O reaction using a carbon aerogel target. A
low-energy ion beam of O was mass separated and implanted in a thin
beryllium foil. The beta particles were counted with plastic scintillator
detectors. We find s. This result is
higher than an average value from six earlier experiments, but agrees more
closely with the most recent previous measurement.Comment: 10 pages, 5 figure
Fluctuation-dissipation theorem and quantum tunneling with dissipation
We suggest to take the fluctuation-dissipation theorem of Callen and Welton
as a basis to study quantum dissipative phenomena (such as macroscopic quantum
tunneling) in a manner analogous to the Nambu-Goldstone theorem for spontaneous
symmetry breakdown. It is shown that the essential physical contents of the
Caldeira-Leggett model such as the suppression of quantum coherence by Ohmic
dissipation are derived from general principles only, namely, the
fluctuation-dissipation theorem and unitarity and causality (i.e., dispersion
relations), without referring to an explicit form of the Lagrangian. An
interesting connection between quantum tunneling with Ohmic dissipation and the
Anderson's orthogonality theorem is also noted.Comment: To appear in Phys. Rev.
Continuous non-perturbative regularization of QED
We regularize in a continuous manner the path integral of QED by construction
of a non-local version of its action by means of a regularized form of Dirac's
functions. Since the action and the measure are both invariant under
the gauge group, this regularization scheme is intrinsically non-perturbative.
Despite the fact that the non-local action converges formally to the local one
as the cutoff goes to infinity, the regularized theory keeps trace of the
non-locality through the appearance of a quadratic divergence in the transverse
part of the polarization operator. This term which is uniquely defined by the
choice of the cutoff functions can be removed by a redefinition of the
regularized action. We notice that as for chiral fermions on the lattice, there
is an obstruction to construct a continuous and non ambiguous regularization in
four dimensions. With the help of the regularized equations of motion, we
calculate the one particle irreducible functions which are known to be
divergent by naive power counting at the one loop order.Comment: 23 pages, LaTeX, 5 Encapsulated Postscript figures. Improved and
revised version, to appear in Phys. Rev.
Canonical approach to 2D induced gravity
Using canonical method the Liouville theory has been obtained as a
gravitational Wess-Zumino action of the Polyakov string. From this approach it
is clear that the form of the Liouville action is the consequence of the
bosonic representation of the Virasoro algebra, and that the coefficient in
front of the action is proportional to the central charge and measures the
quantum braking of the classical symmetry.Comment: RevTeX, 19 page
Fluctuation-dissipation theorem and quantum tunneling with dissipation at finite temperature
A reformulation of the fluctuation-dissipation theorem of Callen and Welton
is presented in such a manner that the basic idea of Feynman-Vernon and
Caldeira -Leggett of using an infinite number of oscillators to simulate the
dissipative medium is realized manifestly without actually introducing
oscillators. If one assumes the existence of a well defined dissipative
coefficient which little depends on the temperature in the energy
region we are interested in, the spontanous and induced emissions as well as
induced absorption of these effective oscillators with correct Bose
distribution automatically appears.
Combined with a dispersion relation, we reproduce the tunneling formula in
the presence of dissipation at finite temperature without referring to an
explicit model Lagrangian. The fluctuation-dissipation theorem of Callen-Welton
is also generalized to the fermionic dissipation (or fluctuation) which allows
a transparent physical interpretation in terms of second quantized fermionic
oscillators. This fermionic version of fluctuation-dissipation theorem may
become relevant in the analyses of, for example, fermion radiation from a black
hole and also supersymmetry at the early universe.Comment: 19 pages. Phys. Rev. E (in press
Anomalous thermodynamics at the micro-scale
Particle motion at the micro-scale is an incessant tug-of-war between thermal
fluctuations and applied forces on one side, and the strong resistance exerted
by fluid viscosity on the other. Friction is so strong that completely
neglecting inertia - the overdamped approximation - gives an excellent
effective description of the actual particle mechanics. In sharp contrast with
this result, here we show that the overdamped approximation dramatically fails
when thermodynamic quantities such as the entropy production in the environment
is considered, in presence of temperature gradients. In the limit of
vanishingly small, yet finite inertia, we find that the entropy production is
dominated by a contribution that is anomalous, i.e. has no counterpart in the
overdamped approximation. This phenomenon, that we call entropic anomaly, is
due to a symmetry-breaking that occurs when moving to the small, finite inertia
limit. Strong production of anomalous entropy is traced back to intense sweeps
down the temperature gradient.Comment: 4 pages, 1 figure, supplementary information uploaded as a separate
pdf file (see other formats link
CP violation in gauge theories
We define the CP transformation properties of scalars, fermions and vectors
in a gauge theory and show that only three types of interactions can lead to CP
violation: scalar interactions, fermion-scalar interactions and
associated with the strong CP problem and which involve only the gauge fields.
For technicolor theories this implies the absence of CP violation within
perturbation theory.Comment: 5 pages, 1 figure, revtex and epsf require
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