56,330 research outputs found

    Quantum Faraday Effect in Double-Dot Aharonov-Bohm Ring

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    We investigate Faraday's law of induction manifested in the quantum state of Aharonov-Bohm loops. In particular, we propose a flux-switching experiment for a double-dot AB ring to verify the phase shift induced by Faraday's law. We show that the induced {\em Faraday phase} is geometric and nontopological. Our study demonstrates that the relation between the local phases of a ring at different fluxes is not arbitrary but is instead determined by Faraday's inductive law, which is in strong contrast to the arbitrary local phase of an Aharonov-Bohm ring for a given flux.Comment: Submitted to Phys. Rev. Let

    Reaction-diffusion with a time-dependent reaction rate: the single-species diffusion-annihilation process

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    We study the single-species diffusion-annihilation process with a time-dependent reaction rate, lambda(t)=lambda_0 t^-omega. Scaling arguments show that there is a critical value of the decay exponent omega_c(d) separating a reaction-limited regime for omega > omega_c from a diffusion-limited regime for omega < omega_c. The particle density displays a mean-field, omega-dependent, decay when the process is reaction limited whereas it behaves as for a constant reaction rate when the process is diffusion limited. These results are confirmed by Monte Carlo simulations. They allow us to discuss the scaling behaviour of coupled diffusion-annihilation processes in terms of effective time-dependent reaction rates.Comment: 11 pages, 9 figures, minor correction

    Is the Number of Giant Arcs in LCDM Consistent With Observations?

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    We use high-resolution N-body simulations to study the galaxy-cluster cross-sections and the abundance of giant arcs in the Λ\LambdaCDM model. Clusters are selected from the simulations using the friends-of-friends method, and their cross-sections for forming giant arcs are analyzed. The background sources are assumed to follow a uniform ellipticity distribution from 0 to 0.5 and to have an area identical to a circular source with diameter 1\arcsec. We find that the optical depth scales as the source redshift approximately as \tau_{1''} = 2.25 \times 10^{-6}/[1+(\zs/3.14)^{-3.42}] (0.6<\zs<7). The amplitude is about 50% higher for an effective source diameter of 0.5\arcsec. The optimal lens redshift for giant arcs with the length-to-width ratio (L/WL/W) larger than 10 increases from 0.3 for \zs=1, to 0.5 for \zs=2, and to 0.7-0.8 for \zs>3. The optical depth is sensitive to the source redshift, in qualitative agreement with Wambsganss et al. (2004). However, our overall optical depth appears to be only \sim 10% to 70% of those from previous studies. The differences can be mostly explained by different power spectrum normalizations (σ8\sigma_8) used and different ways of determining the L/WL/W ratio. Finite source size and ellipticity have modest effects on the optical depth. We also found that the number of highly magnified (with magnification μ>10|\mu|>10) and ``undistorted'' images (with L/W<3L/W<3) is comparable to the number of giant arcs with μ>10|\mu|>10 and L/W>10L/W>10. We conclude that our predicted rate of giant arcs may be lower than the observed rate, although the precise `discrepancy' is still unclear due to uncertainties both in theory and observations.Comment: Revised version after the referee's reports (32 pages,13figures). The paper has been significantly revised with many additions. The new version includes more detailed comparisons with previous studies, including the effects of source size and ellipticity. New discussions about the redshift distribution of lensing clusters and the width of giant arcs have been adde

    Separable states and the geometric phases of an interacting two-spin system

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    It is known that an interacting bipartite system evolves as an entangled state in general, even if it is initially in a separable state. Due to the entanglement of the state, the geometric phase of the system is not equal to the sum of the geometric phases of its two subsystems. However, there may exist a set of states in which the nonlocal interaction does not affect the separability of the states, and the geometric phase of the bipartite system is then always equal to the sum of the geometric phases of its subsystems. In this paper, we illustrate this point by investigating a well known physical model. We give a necessary and sufficient condition in which a separable state remains separable so that the geometric phase of the system is always equal to the sum of the geometric phases of its subsystems.Comment: 13 page

    A weighted cellular matrix-tree theorem, with applications to complete colorful and cubical complexes

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    We present a version of the weighted cellular matrix-tree theorem that is suitable for calculating explicit generating functions for spanning trees of highly structured families of simplicial and cell complexes. We apply the result to give weighted generalizations of the tree enumeration formulas of Adin for complete colorful complexes, and of Duval, Klivans and Martin for skeleta of hypercubes. We investigate the latter further via a logarithmic generating function for weighted tree enumeration, and derive another tree-counting formula using the unsigned Euler characteristics of skeleta of a hypercube and the Crapo β\beta-invariant of uniform matroids.Comment: 22 pages, 2 figures. Sections 6 and 7 of previous version simplified and condensed. Final version to appear in J. Combin. Theory Ser.

    An alternative formulation of classical electromagnetic duality

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    By introducing a doublet of electromagnetic four dimensional vector potentials, we set up a manifestly Lorentz covariant and SO(2) duality invariant classical field theory of electric and magnetic charges. In our formulation one does not need to introduce the concept of Dirac string.Comment: 14 pages, no figures, Latex, minor corrections, references and acknowledgements adde

    Origins of the Isospin Violation of Dark Matter Interactions

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    Light dark matter (DM) with a large DM-nucleon spin-independent cross section and furthermore proper isospin violation (ISV) fn/fp0.7f_n/f_p\approx-0.7 may provide a way to understand the confusing DM direct detection results. Combing with the stringent astrophysical and collider constraints, we systematically investigate the origin of ISV first via general operator analyses and further via specifying three kinds of (single) mediators: A light ZZ' from chiral U(1)XU(1)_X, an approximate spectator Higgs doublet (It can explain the W+jjW+jj anomaly simultaneously) and color triplets. In addition, although ZZ' from an exotic U(1)XU(1)_X mixing with U(1)YU(1)_Y generating fn=0f_n=0, we can combine it with the conventional Higgs to achieve proper ISV. As a concrete example, we propose the U(1)XU(1)_X model where the U(1)XU(1)_X charged light sneutrino is the inelastic DM, which dominantly annihilates to light dark states such as ZZ' with sub-GeV mass. This model can address the recent GoGeNT annual modulation consistent with other DM direct detection results and free of exclusions.Comment: References added and English greatly improve
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