25,419 research outputs found
Finding passwords by random walks: How long does it take?
We compare an efficiency of a deterministic "lawnmower" and random search
strategies for finding a prescribed sequence of letters (a password) of length
M in which all letters are taken from the same Q-ary alphabet. We show that at
best a random search takes two times longer than a "lawnmower" search.Comment: To appear in J. Phys. A, special issue on "Random Search Problem:
Trends and Perspectives", eds.: MEG da Luz, E Raposo, GM Viswanathan and A
Grosber
Test of CPT and Lorentz invariance from muonium spectroscopy
Following a suggestion of Kostelecky et al. we have evaluated a test of CPT
and Lorentz invariance from the microwave spectroscopy of muonium. Hamiltonian
terms beyond the standard model violating CPT and Lorentz invariance would
contribute frequency shifts and to
and , the two transitions involving muon spin flip, which were
precisely measured in ground state muonium in a strong magnetic field of 1.7 T.
The shifts would be indicated by anti-correlated oscillations in and
at the earth's sidereal frequency. No time dependence was found in
or at the level of 20 Hz, limiting the size of some CPT
and Lorentz violating parameters at the level of GeV,
representing Planck scale sensitivity and an order of magnitude improvement in
sensitivity over previous limits for the muon.Comment: 4 pages, 4 figures, uses REVTeX and epsf, submitted to Phys. Rev.
Let
One-Loop Renormalization of Lorentz-Violating Electrodynamics
We show that the general Lorentz- and CPT-violating extension of quantum
electrodynamics is one-loop renormalizable. The one-loop Lorentz-violating beta
functions are obtained, and the running of the coefficients for Lorentz and CPT
violation is determined. Some implications for theory and experiment are
discussed.Comment: 12 pages, accepted for publication in Physical Review
Current and universal scaling in anomalous transport
Anomalous transport in tilted periodic potentials is investigated within the
framework of the fractional Fokker-Planck dynamics and the underlying
continuous time random walk. The analytical solution for the stationary,
anomalous current is obtained in closed form. We derive a universal scaling law
for anomalous diffusion occurring in tilted periodic potentials. This scaling
relation is corroborated with precise numerical studies covering wide parameter
regimes and different shapes for the periodic potential, being either symmetric
or ratchet-like ones
The Equivalence Principle in the Non-baryonic Regime
We consider the empirical validity of the equivalence principle for
non-baryonic matter. Working in the context of the TH\epsilon\mu formalism, we
evaluate the constraints experiments place on parameters associated with
violation of the equivalence principle (EVPs) over as wide a sector of the
standard model as possible. Specific examples include new parameter constraints
which arise from torsion balance experiments, gravitational red shift,
variation of the fine structure constant, time-dilation measurements, and
matter/antimatter experiments. We find several new bounds on EVPs in the
leptonic and kaon sectors.Comment: 22 pages, late
Optimizing the Earth-LISA "rendez-vous"
We present a general survey of heliocentric LISA orbits, hoping it might help
in the exercise of rescoping the mission. We try to semi-analytically optimize
the orbital parameters in order to minimize the disturbances coming from the
Earth-LISA interaction. In a set of numerical simulations we include
nonautonomous perturbations and provide an estimate of Doppler shift and
breathing as a function of the trailing angle.Comment: 18 pages, 16 figures. Submitted on CQ
CPT and Lorentz Tests in Hydrogen and Antihydrogen
Signals for CPT and Lorentz violation at the Planck scale may arise in
hydrogen and antihydrogen spectroscopy. We show that certain 1S-2S and
hyperfine transitions can exhibit theoretically detectable effects unsuppressed
by any power of the fine-structure constant.Comment: 4 pages REVTeX, submitted for publicatio
Ames collaborative study of cosmic ray neutrons
The results of a collaborative study to define both the neutron flux and the spectrum more precisely and to develop a dosimetry package that can be flown quickly to altitude for solar flare events are described. Instrumentation and analysis techniques were used which were developed to measure accelerator-produced radiation. The instruments were flown in the Ames Research Center high altitude aircraft. Neutron instrumentation consisted of Bonner spheres with both active and passive detector elements, threshold detectors of both prompt-counter and activation-element types, a liquid scintillation spectrometer based on pulse-shape discrimination, and a moderated BF3 counter neutron monitor. In addition, charged particles were measured with a Reuter-Stokes ionization chamber system and dose equivalent with another instrument. Preliminary results from the first series of flights at 12.5 km (41,000 ft) are presented, including estimates of total neutron flux intensity and spectral shape and of the variation of intensity with altitude and geomagnetic latitude
Observation of power-law scaling for phase transitions in linear trapped ion crystals
We report an experimental confirmation of the power-law relationship between
the critical anisotropy parameter and ion number for the linear-to-zigzag phase
transition in an ionic crystal. Our experiment uses laser cooled calcium ions
confined in a linear radio-frequency trap. Measurements for up to 10 ions are
in good agreement with theoretical and numeric predictions. Implications on an
upper limit to the size of data registers in ion trap quantum computers are
discussed.Comment: Physical Review Letters in press, 4 pages, 4 figure
On the Geometry and Entropy of Non-Hamiltonian Phase Space
We analyze the equilibrium statistical mechanics of canonical, non-canonical
and non-Hamiltonian equations of motion by throwing light into the peculiar
geometric structure of phase space. Some fundamental issues regarding time
translation and phase space measure are clarified. In particular, we emphasize
that a phase space measure should be defined by means of the Jacobian of the
transformation between different types of coordinates since such a determinant
is different from zero in the non-canonical case even if the phase space
compressibility is null. Instead, the Jacobian determinant associated with
phase space flows is unity whenever non-canonical coordinates lead to a
vanishing compressibility, so that its use in order to define a measure may not
be always correct. To better illustrate this point, we derive a mathematical
condition for defining non-Hamiltonian phase space flows with zero
compressibility. The Jacobian determinant associated with time evolution in
phase space is altogether useful for analyzing time translation invariance. The
proper definition of a phase space measure is particularly important when
defining the entropy functional in the canonical, non-canonical, and
non-Hamiltonian cases. We show how the use of relative entropies can circumvent
some subtle problems that are encountered when dealing with continuous
probability distributions and phase space measures. Finally, a maximum
(relative) entropy principle is formulated for non-canonical and
non-Hamiltonian phase space flows.Comment: revised introductio
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