Ab initio lattice results for Fermi polarons in two dimensions

We investigate the attractive Fermi polaron problem in two dimensions using non-perturbative Monte Carlo simulations. We introduce a new Monte Carlo algorithm called the impurity lattice Monte Carlo method. This algorithm samples the path integral in a computationally efficient manner and has only small sign oscillations for systems with a single impurity. As a benchmark of the method, we calculate the universal polaron energy in three dimensions in the scale-invariant unitarity limit and find agreement with published results. We then present the first fully non-perturbative calculations of the polaron energy in two dimensions and density correlations between the impurity and majority particles in the limit of zero range interactions. We find evidence for a smooth crossover transition from fermionic quasiparticle to molecular state as a function of interaction strength.Comment: Includes new results on density-density correlations. Final version as will appear in Phys. Rev. Let

Benchmark calculations for elastic fermion-dimer scattering

We present continuum and lattice calculations for elastic scattering between a fermion and a bound dimer in the shallow binding limit. For the continuum calculation we use the Skorniakov-Ter-Martirosian (STM) integral equation to determine the scattering length and effective range parameter to high precision. For the lattice calculation we use the finite-volume method of L\"uscher. We take into account topological finite-volume corrections to the dimer binding energy which depend on the momentum of the dimer. After subtracting these effects, we find from the lattice calculation kappa a_fd = 1.174(9) and kappa r_fd = -0.029(13). These results agree well with the continuum values kappa a_fd = 1.17907(1) and kappa r_fd = -0.0383(3) obtained from the STM equation. We discuss applications to cold atomic Fermi gases, deuteron-neutron scattering in the spin-quartet channel, and lattice calculations of scattering for nuclei and hadronic molecules at finite volume.Comment: 16 pages, 5 figure

PMH14 HEALTH CARE EXPENDITURES OF PATIENTS WITH MAJOR DEPRESSIVE DISORDER AND POST TRAUMATIC STRESS DISORDER

A computer model is presented that describes soleus H-reflex recruitment as a function of electric stimulus intensity. The model consists of two coupled non-linear transfer functions. The first transfer function describes the activation of muscle spindle (Ia) afferent terminals as a function of the electric stimulus intensity; whereas the second describes the activation of a number of motoneurons as a function of the number of active Ia afferent terminals. The effect of change in these transfer functions on the H-reflex recruitment curve is simulated. In spastic patients, a higher average maximal H-response amplitude is observed in combination with a decreased H-reflex threshold. Vibration of the Achilles tendon reduces the H-reflex amplitude, presumably by reducing the excitatory afferent input. Vibratory inhibition is diminished in spasticity. In the model, the afferent-motoneuron transfer function was modified to represent the possible alterations occurring in spasticity. The simulations show that vibratory suppression of the H-reflex is determined only in part by the inhibition level of the afferent input. With a constant level of presynaptic inhibition, the suppression of reflexes of different sizes may vary. A lowering of the motoneuron activation thresholds in spastic patients will directly contribute to a decrease of vibratory inhibition in spasticit

Topological phases for bound states moving in a finite volume

We show that bound states moving in a finite periodic volume have an energy correction which is topological in origin and universal in character. The topological volume corrections contain information about the number and mass of the constituents of the bound states. These results have broad applications to lattice calculations involving nucleons, nuclei, hadronic molecules, and cold atoms. We illustrate and verify the analytical results with several numerical lattice calculations.Comment: 4 pages, 1 figure, version to appear in Phys. Rev. D Rapid Communication

Coherent instabilities in a semiconductor laser with fast gain recovery

We report the observation of a coherent multimode instability in quantum cascade lasers (QCLs), which is driven by the same fundamental mechanism of Rabi oscillations as the elusive Risken-Nummedal-Graham-Haken (RNGH) instability predicted 40 years ago for ring lasers. The threshold of the observed instability is significantly lower than in the original RNGH instability, which we attribute to saturable-absorption nonlinearity in the laser. Coherent effects, which cannot be reproduced by standard laser rate equations, can play therefore a key role in the multimode dynamics of QCLs, and in lasers with fast gain recovery in general.Comment: 5 pages, 4 figure

Non-relativistic bound states in a finite volume

We derive general results for the mass shift of bound states with angular momentum l >= 1 in a periodic cubic box in two and three spatial dimensions. Our results have applications to lattice simulations of hadronic molecules, halo nuclei, and Feshbach molecules. The sign of the mass shift can be related to the symmetry properties of the state under consideration. We verify our analytical results with explicit numerical calculations. Moreover, we comment on the relations connecting the effective range parameter, the binding momentum of a given state and the asymptotic normalization coefficient of the corresponding wave function. We give explicit expressions for this relation in the shallow binding limit.Comment: 26 pages, 4 figure

Improving the sensitivity of future GW observatories in the 1-10 Hz band: Newtonian and seismic noise

The next generation gravitational wave interferometric detectors will likely be underground detectors to extend the GW detection frequency band to frequencies below the Newtonian noise limit. Newtonian noise originates from the continuous motion of the Earth’s crust driven by human activity, tidal stresses and seismic motion, and from mass density fluctuations in the atmosphere. It is calculated that on Earth’s surface, on a typical day, it will exceed the expected GW signals at frequencies below 10 Hz. The noise will decrease underground by an unknown amount. It is important to investigate and to quantify this expected reduction and its effect on the sensitivity of future detectors, to plan for further improvement strategies. We report about some of these aspects. Analytical models can be used in the simplest scenarios to get a better qualitative and semi-quantitative understanding. As more complete modeling can be done numerically, we will discuss also some results obtained with a finite-element-based modeling tool. The method is verified by comparing its results with the results of analytic calculations for surface detectors. A key point about noise models is their initial parameters and conditions, which require detailed information about seismic motion in a real scenario. We will describe an effort to characterize the seismic activity at the Homestake mine which is currently in progress. This activity is specifically aimed to provide informations and to explore the site as a possible candidate for an underground observatory. Although the only compelling reason to put the interferometer underground is to reduce the Newtonian noise, we expect that the more stable underground environment will have a more general positive impact on the sensitivity.We will end this report with some considerations about seismic and suspension noise

Insulin-induced remission in new-onset NOD mice is maintained by the PD-1–PD-L1 pathway

The past decade has seen a significant increase in the number of potentially tolerogenic therapies for treatment of new-onset diabetes. However, most treatments are antigen nonspecific, and the mechanism for the maintenance of long-term tolerance remains unclear. In this study, we developed an antigen-specific therapy, insulin-coupled antigen-presenting cells, to treat diabetes in nonobese diabetic mice after disease onset. Using this approach, we demonstrate disease remission, inhibition of pathogenic T cell proliferation, decreased cytokine production, and induction of anergy. Moreover, we show that robust long-term tolerance depends on the programmed death 1 (PD-1)–programmed death ligand (PD-L)1 pathway, not the distinct cytotoxic T lymphocyte–associated antigen 4 pathway. Anti–PD-1 and anti–PD-L1, but not anti–PD-L2, reversed tolerance weeks after tolerogenic therapy by promoting antigen-specific T cell proliferation and inflammatory cytokine production directly in infiltrated tissues. PD-1–PD-L1 blockade did not limit T regulatory cell activity, suggesting direct effects on pathogenic T cells. Finally, we describe a critical role for PD-1–PD-L1 in another powerful immunotherapy model using anti-CD3, suggesting that PD-1–PD-L1 interactions form part of a common pathway to selectively maintain tolerance within the target tissues