Localization Lifetime of a Many-Body System with Periodic Constructed Disorder

We show that, in a many-body system, all particles can be strongly confined to the initially occupied sites for a time that scales as a high power of the ratio of the bandwidth of site energies to the hopping amplitude. Such time-domain formulation is complementary to the formulation of the many-body localization of all stationary states with a large localization length. The long localization lifetime is achieved by constructing a periodic sequence of site energies with a large period in a one-dimensional chain. The scaling of the localization lifetime is independent of the number of particles for a broad range of the coupling strength. The analytical results are confirmed by numerical calculations

Comment on "Kinetic theory for a mobile impurity in a degenerate Tonks-Girardeau gas"

In a recent paper, arxiv:1402.6362, Gamayun, Lychkovskiy, and Cheianov studied the dynamics of a mobile impurity embedded into a one-dimensional Tonks-Girardeau gas of strongly interacting bosons. Employing the Boltzmann equation approach, they arrived at the following main conclusions: (i) a light impurity, being accelerated by a constant force does not exhibit Bloch oscillations; (ii) a heavy impurity does undergo Bloch oscillations, accompanied by a drift with the velocity proportional to the square root of force. In this comment we argue that the result (i) is an artifact of the classical Boltzmann approximation, which misses the formation of the (quasi) bound-state between the impurity and a hole. Result (ii), while not valid at asymptotically small force, indeed reflects an interesting intermediate-force behavior. Here we clarify its limits of applicability and extend beyond the Tonks-Girardeau limit.Comment: 2 pages, 1 figur

Composite Topological Excitations in Ferromagnet-Superconductor Heterostructures

We investigate the formation of a new type of composite topological excitation -- the skyrmion-vortex pair (SVP) -- in hybrid systems consisting of coupled ferromagnetic and superconducting layers. Spin-orbit interaction in the superconductor mediates a magnetoelectric coupling between the vortex and the skyrmion, with a sign (attractive or repulsive) that depends on the topological indices of the constituents. We determine the conditions under which a bound SVP is formed, and characterize the range and depth of the effective binding potential through analytical estimates and numerical simulations. Furthermore, we develop a semiclassical description of the coupled skyrmion-vortex dynamics and discuss how SVPs can be controlled by applied spin currents.Comment: Final version accepted by Physical Review Letters; 9 pages, 5 figure

Critical velocity of a mobile impurity in one-dimensional quantum liquids

We study the notion of superfluid critical velocity in one spatial dimension. It is shown that for heavy impurities with mass $M$ exceeding a critical mass $M_\mathrm{c}$, the dispersion develops periodic metastable branches resulting in dramatic changes of dynamics in the presence of an external driving force. In contrast to smooth Bloch Oscillations for $M<M_\mathrm{c}$, a heavy impurity climbs metastable branches until it reaches a branch termination point or undergoes a random tunneling event, both leading to an abrupt change in velocity and an energy loss. This is predicted to lead to a non-analytic dependence of the impurity drift velocity on small forces.Comment: 5 pages, 2 figures; New version with Supplemental Material (3 pages, 6 figures); Accepted to PR

Obesity is Associated with More Disability at Presentation and After Treatment in Low Back Pain but Not in Neck Pain: Findings from the OIOC Registry

Background: The influence on the treatment response in patients with low back pain (LBP) and neck pain (NP) is unknown. The aim of the study was to investigate the influence of body weight in patients with low back pain (LBP) and neck pain (NP) on baseline and end of treatment disability. Methods: Cross-sectional analysis of baseline factors. Longitudinal analysis of prospectively collected patient information at an outpatient physical therapy registry (data from June 2010 to December 2012). WHO-BMI classification was used: underweight, lean, overweight, obesity class I, obesity class II and III. The influence of body weight and a predefined set of confounders was analyzed by multiple regression models. Results: In LBP, disability increased with increasing BMI [lean = reference, obesity class I Beta 5.41 (95 % CI 0.75; 10.07), obesity class II-III Beta 7.58 (95 % CI 2.13; 13.03)]. Compared to lean patients, disability after treatment improved in overweight subjects [Beta −3.90 (95 % CI −7.4; −0.41)] but not in subjects with obesity class II–III [Beta 3.43 (95 % CI −3.81; 10.68)]. There were insufficient patients in the sample with severe obesity and therefore this trend has to be confirmed. The likelihood for meaningful important change (MID) was similar in all BMI subgroups. For patients with NP, BMI was not associated with baseline disability, and did not predict end of treatment disability or the likelihood of a MID. These findings must be interpreted with caution as BMI subgroups did not meet the required sample size. Conclusion: Overweight and obesity are associated with higher levels of disability before treatment in LBP patients, but not in NP. In severely obese patients class II–III with LBP the rate of MID was lowest indicating that these patients experienced the least treatment response compared to the other groups. Further studies should address the impact of severe obesity on the prognosis of LBP. In patients with LBP, severe obesity may be an important factor to consider during the physical therapy treatment. In particular, combined treatment strategies combining weight management, cardiovascular fitness, and low back pain rehabilitation should be investigated

Stability of Neutrinos in the Singlet Majoron Model

We show that there is no one-loop enhancement of the rate for a light neutrino to decay into a lighter neutrino plus a majoron, contrary to a recent claim. Thus the light neutrinos must satisfy the cosmological bound of having masses less than 35 eV in the singlet majoron model, or else violate the constraint imposed by galaxy formation. In the latter case, $\nu_\tau$ could have a mass between 40 and 500 keV, while satisfying all other cosmological constraints.Comment: 11 pp., latex, UMN-TH-1218-93. Correct nucleosynthesis bound of 500 keV on nu_tau mass is incorporated; one-loop electroweak contribution to neutrino mass is correcte

Inviscid dynamical structures near Couette flow

Consider inviscid fluids in a channel {-1<y<1}. For the Couette flow v_0=(y,0), the vertical velocity of solutions to the linearized Euler equation at v_0 decays in time. At the nonlinear level, such inviscid damping has not been proved. First, we show that in any (vorticity) H^{s}(s<(3/2)) neighborhood of Couette flow, there exist non-parallel steady flows with arbitrary minimal horizontal period. This implies that nonlinear inviscid damping is not true in any (vorticity) H^{s}(s<(3/2)) neighborhood of Couette flow and for any horizontal period. Indeed, the long time behavior in such neighborhoods are very rich, including nontrivial steady flows, stable and unstable manifolds of nearby unstable shears. Second, in the (vorticity) H^{s}(s>(3/2)) neighborhood of Couette, we show that there exist no non-parallel steadily travelling flows v(x-ct,y), and no unstable shears. This suggests that the long time dynamics in H^{s}(s>(3/2)) neighborhoods of Couette might be much simpler. Such contrasting dynamics in H^{s} spaces with the critical power s=(3/2) is a truly nonlinear phenomena, since the linear inviscid damping near Couette is true for any initial vorticity in L^2

New vector-scalar contributions to neutrinoless double beta decay and constraints on R-parity violation

We show that in minimal supersymmetric standard model (MSSM) with R-parity breaking as well as in the left-right symmetric model, there are new observable contributions to neutrinoless double beta decay arising from hitherto overlooked diagrams involving the exchange of one W boson and one scalar boson. In particular, in the case of MSSM, the present experimental bounds on neutrinoless double beta decay lifetime improves the limits on certain R-parity violating couplings by about two orders of magnitude. It is shown that similar diagrams also lead to enhanced rates for $\mu^-\rightarrow e^+$ conversion in nuclei, which are in the range accessible to ongoing experiments.Comment: Latex file; 9 pages; 3 figures available on reques