39,179 research outputs found
Geometric phase and gauge theory structure in quantum computing
We discuss the presence of a geometrical phase in the evolution of a qubit
state and its gauge structure. The time evolution operator is found to be the
free energy operator, rather than the Hamiltonian operator.Comment: 5 pages, presented at Fifth International Workshop DICE2010:
Space-Time-Matter - current issues in quantum mechanics and beyond,
Castiglioncello (Tuscany), September 13-17, 201
Non-quantized Dirac monopoles and strings in the Berry phase of anisotropic spin systems
The Berry phase of an anisotropic spin system that is adiabatically rotated
along a closed circuit C is investigated. It is shown that the Berry phase
consists of two contributions: (i) a geometric contribution which can be
interpreted as the flux through C of a non-quantized Dirac monopole, and (ii) a
topological contribution which can be interpreted as the flux through C of a
Dirac string carrying a non-quantized flux, i.e., a spin analogue of the
Aharonov-Bohm effect. Various experimental consequences of this novel effect
are discussed.Comment: 4 pages, 3 figures (RevTeX + eps); v2 (revised paper): 4 pages, 4
figure
Coulomb force effects in low-energy -deuteron scattering
The -proton Coulomb interaction is included in the description of
-deuteron scattering using the screening and renormalization approach
in the framework of momentum-space three-particle equations. The technical
reliability of the method is demonstrated. Large Coulomb-force effects are
found.Comment: To be published in Phys. Rev.
Quasi-particle dephasing time in disordered d-wave superconductors
We evaluate the low-temperature cutoff for quantum interference 1/tf induced
in a d-wave superconductor by the diffusion enhanced quasiparticle interactions
in the presence of disorder. We carry out our analysis in the framework of the
non-linear sigma-model which allows a direct calculation of 1/tf, as the mass
of the transverse modes of the theory. Only the triplet amplitude in the
particle-hole channel and the Cooper amplitude with is pairing symmetry
contribute to 1/tf. We discuss the possible relevance of our results to the
present disagreement between thermal transport data in cuprates and the
localization theory for d-wave quasiparticles
Tabulation of PVI Transcendents and Parametrization Formulas (August 17, 2011)
The critical and asymptotic behaviors of solutions of the sixth Painlev\'e
equation PVI, obtained in the framework of the monodromy preserving deformation
method, and their explicit parametrization in terms of monodromy data, are
tabulated.Comment: 30 pages, 1 figure; Nonlinearity 201
Monte Carlo Markov Chain parameter estimation in semi-analytic models of galaxy formation
We present a statistical exploration of the parameter space of the De Lucia and Blaizot version of the Munich semi-analytic (SA) model built upon the Millennium dark matter simulation. This is achieved by applying a Monte Carlo Markov Chain method to constrain the six free parameters that define the stellar and black hole mass functions at redshift zero. The model is tested against three different observational data sets, including the galaxy K-band luminosity function, B - V colours and the black hole-bulge mass relation, separately and combined, to obtain mean values, confidence limits and likelihood contours for the best-fitting model. Using each observational data set independently, we discuss how the SA model parameters affect each galaxy property and find that there are strong correlations between them. We analyse to what extent these are simply reflections of the observational constraints, or whether they can lead to improved understandings of the physics of galaxy formation.
When all the observations are combined, we find reasonable agreement between the majority of the previously published parameter values and our confidence limits. However, the need to suppress dwarf galaxy formation requires the strength of the supernova feedback to be significantly higher in our best-fitting solution than in previous work.
To balance this, we require the feedback to become ineffective in haloes of lower mass than before, so as to permit the formation of sufficient high-luminosity galaxies: unfortunately, this leads to an excess of galaxies around L*. Although the best fit is formally consistent with the data, there is no region of parameter space that reproduces the shape of galaxy luminosity function across the whole magnitude range.
For our best fit, we present the model predictions for the bJ-band luminosity and stellar mass functions. We find a systematic disagreement between the observed mass function and the predictions from the K-band constraint, which we explain in light of recent works that suggest uncertainties of up to 0.3 dex in the mass determination from stellar population synthesis models.
We discuss modifications to the SA model that might simultaneously improve the fit to the observed mass function and reduce the reliance on excessive supernova feedback in small haloes
Wavelets Applied to the Detection of Point Sources of UHECRs
In this work we analyze the effect of smoothing maps containing arrival
directions of cosmic rays with a gaussian kernel and kernels of the mexican hat
wavelets of orders 1, 2 and 3. The analysis is performed by calculating the
amplification of the signal-to-noise ratio for several anisotropy patterns
(noise) and different number of events coming from a simulated source (signal)
for an ideal detector capable of observing the full sky with equal probability.
We extend this analysis for a virtual detector located within the array of
detectors of the Pierre Auger Observatory, considering an acceptance law.Comment: 9 pages, 8 figures. Proceedings of the Young Researchers Meeting,
2010. Available in:
http://www.ifi.unicamp.br/physicae/ojs-2.1.1/index.php/physicae/article/view/191;
Physicae, Proceedings of the Young Researchers Meeting, Vol 1, 201
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