Classical Three-Box "paradox"

A simple classical probabilistic system (a simple card game) classically exemplifies Aharonov and Vaidman's "Three-Box 'paradox'" [J. Phys. A 24, 2315 (1991)], implying that the Three-Box example is neither quantal nor a paradox and leaving one less difficulty to busy the interpreters of quantum mechanics. An ambiguity in the usual expression of the retrodiction formula is shown to have misled Albert, Aharonov, and D'Amato [Phys. Rev. Lett. 54, 5 (1985)] to a result not, in fact, "curious"; the discussion illustrates how to avoid this ambiguity.Comment: 10 pages. v4: As published, with corrections and updated reference

Anomalous Pinning Fields in Helical Magnets: Screening of the Quasiparticle Interaction

The spin-orbit interaction strength g_so in helical magnets determines both the pitch wave number q and the critical field H_c1 where the helix aligns with an external magnetic field. Within a standard Landau-Ginzburg-Wilson (LGW) theory, a determination of g_so in MnSi and FeGe from these two observables yields values that differ by a factor of 20. This discrepancy is remedied by considering the fermionic theory underlying the LGW theory, and in particular the effects of screening on the effective electron-electron interaction that results from an exchange of helical fluctuations.Comment: 4pp, 2 fig

Phase diagram of glassy systems in an external field

We study the mean-field phase diagram of glassy systems in a field pointing in the direction of a metastable state. We find competition among a ``magnetized'' and a ``disordered'' phase, that are separated by a coexistence line as in ordinary first order phase transitions. The coexistence line terminates in a critical point, which in principle can be observed in numerical simulations of glassy models.Comment: 4 pages, 5 figure

Numerical study of a short-range p-spin glass model in three dimensions

In this work we study numerically a short range p-spin glass model in three dimensions. The behaviour of the model appears to be remarkably different from mean field predictions. In fact it shares some features typical of models with full replica-symmetry breaking (FRSB). Nevertheless, we believe that the transition that we study is intrinsically different from the FRSB and basically due to non-perturbative contributions. We study both the statics and the dynamics of the system which seem to confirm our conjectures.Comment: 20 pages, 15 figure

Adiabatic times for Markov chains and applications

We state and prove a generalized adiabatic theorem for Markov chains and provide examples and applications related to Glauber dynamics of Ising model over Z^d/nZ^d. The theorems derived in this paper describe a type of adiabatic dynamics for l^1(R_+^n) norm preserving, time inhomogeneous Markov transformations, while quantum adiabatic theorems deal with l^2(C^n) norm preserving ones, i.e. gradually changing unitary dynamics in C^n

Transport Anomalies and Marginal Fermi-Liquid Effects at a Quantum Critical Point

The conductivity and the tunneling density of states of disordered itinerant electrons in the vicinity of a ferromagnetic transition at low temperature are discussed. Critical fluctuations lead to nonanalytic frequency and temperature dependences that are distinct from the usual long-time tail effects in a disordered Fermi liquid. The crossover between these two types of behavior is proposed as an experimental check of recent theories of the quantum ferromagnetic critical behavior. In addition, the quasiparticle properties at criticality are shown to be those of a marginal Fermi liquid.Comment: 4pp., REVTeX, no figs, final version as publishe

Quantum critical behavior in disordered itinerant ferromagnets: Logarithmic corrections to scaling

The quantum critical behavior of disordered itinerant ferromagnets is determined exactly by solving a recently developed effective field theory. It is shown that there are logarithmic corrections to a previous calculation of the critical behavior, and that the exact critical behavior coincides with that found earlier for a phase transition of undetermined nature in disordered interacting electron systems. This confirms a previous suggestion that the unspecified transition should be identified with the ferromagnetic transition. The behavior of the conductivity, the tunneling density of states, and the phase and quasiparticle relaxation rates across the ferromagnetic transition is also calculated.Comment: 15pp., REVTeX, 8 eps figs, final version as publishe

An Experimentally Realizable Weiss Model for Disorder-Free Glassiness

We summarize recent work on a frustrated periodic long-range Josephson array in a parameter regime where its dynamical behavior is identical to that of the $p=4$ disordered spherical model. We also discuss the physical requirements imposed by the theory on the experimental realization of this superconducting network.Comment: 6 pages, LaTeX, 2 Postscript figure

Theory of Helimagnons in Itinerant Quantum Systems IV: Transport in the Weak-Disorder Regime

We apply a recent quasiparticle model for the electronic properties of metallic helimagnets to calculate the transport properties of three-dimensional systems in the helically ordered phase. We focus on the ballistic regime tau^2 T epsilon_F >> 1 at weak disorder (large elastic mean-free time tau) or intermediate temperature. In this regime, we find a leading temperature dependence of the electrical conductivity proportional to T. This is much stronger than either the Fermi-liquid contribution (T^2) or the contribution from helimagnon scattering in the clean limit (T^{5/2}). It is reminiscent of the behavior of non-magnetic two-dimensional metals, but the sign of the effect is opposite to that in the non-magnetic case. Experimental consequences of this result are discussed.Comment: 17pp, 5 fig

Parallaxes of southern extremely cool objects (PARSEC). II : Spectroscopic follow-up and parallaxes of 52 targets

We present near-infrared spectroscopy for 52 ultracool dwarfs, including two newly discovered late-M dwarfs, one new late-M subdwarf candidate, three new L, and four new T dwarfs. We also present parallaxes and proper motions for 21 of them. Four of the targets presented here have previous parallax measurements, while all the others are new values. This allow us to populate further the spectral sequence at early types (L0-L4). Combining the astrometric parameters with the new near-infrared spectroscopy presented here, we are able to investigate further the nature of some of the objects. In particular, we find that the peculiar blue L1 dwarf SDSS J133148.92-011651.4 is a metal-poor object, likely a member of the galactic thick disk. We discover a new M subdwarf candidate, 2MASS J20115649-6201127. We confirm the low-gravity nature of EROS-MP J0032-4405, DENIS-P J035726.9-441730, and 2MASS J22134491-2136079. We present two new metal-poor dwarfs: the L4pec 2MASS J19285196-4356256 and the M7pec SIPS2346-5928. We also determine the effective temperature and bolometric luminosity of the 21 targets with astrometric measurements, and we obtain a new polynomial relation between effective temperature and near-infrared spectral type. The new fit suggests a flattening of the sequence at the transition between M and L spectral types. This could be an effect of dust formation, which causes a more rapid evolution of the spectral features as a function of the effective temperature.Peer reviewe