Generalized Involution Models for Wreath Products

We prove that if a finite group $H$ has a generalized involution model, as defined by Bump and Ginzburg, then the wreath product $H \wr S_n$ also has a generalized involution model. This extends the work of Baddeley concerning involution models for wreath products. As an application, we construct a Gelfand model for wreath products of the form $A \wr S_n$ with $A$ abelian, and give an alternate proof of a recent result due to Adin, Postnikov, and Roichman describing a particularly elegant Gelfand model for the wreath product \ZZ_r \wr S_n. We conclude by discussing some notable properties of this representation and its decomposition into irreducible constituents, proving a conjecture of Adin, Roichman, and Postnikov's.Comment: 29 page

DMTPC: A dark matter detector with directional sensitivity

By correlating nuclear recoil directions with the Earth's direction of motion through the Galaxy, a directional dark matter detector can unambiguously detect Weakly Interacting Massive Particles (WIMPs), even in the presence of backgrounds. Here, we describe the Dark Matter Time-Projection Chamber (DMTPC) detector, a TPC filled with CF4 gas at low pressure (0.1 atm). Using this detector, we have measured the vector direction (head-tail) of nuclear recoils down to energies of 100 keV with an angular resolution of <15 degrees. To study our detector backgrounds, we have operated in a basement laboratory on the MIT campus for several months. We are currently building a new, high-radiopurity detector for deployment underground at the Waste Isolation Pilot Plant facility in New Mexico.Comment: 4 pages, 2 figures, proceedings for the CIPANP 2009 conference, May 26-31, 200

Differential postural effects of plantar-flexor muscles fatigue under normal, altered and improved vestibular and neck somatosensory conditions

The aim of the present study was to assess the effects of plantar-flexor muscles fatigue on postural control during quiet standing under normal, altered and improved vestibular and neck somatosensory conditions. To address this objective, young male university students were asked to stand upright as still as possible with their eyes closed in two conditions of No Fatigue and Fatigue of the plantar-flexor muscles. In Experiment 1 (n=15), the postural task was executed in two Neutral head and Head tilted backward postures, recognized to degrade vestibular and neck somatosensory information. In Experiment 2 (n=15), the postural task was executed in two conditions of No tactile and Tactile stimulation of the neck provided by the application of strips of adhesive bandage to the skin over and around the neck. Centre of foot pressure displacements were recorded using a force platform. Results showed that (1) the Fatigue condition yielded increased CoP displacements relative to the No Fatigue condition (Experiment 1 and Experiment 2), (2) this destabilizing effect was more accentuated in the Head tilted backward posture than Neutral head posture (Experiment 1) and (3) this destabilizing effect was less accentuated in the condition of Tactile stimulation than that of No tactile stimulation of the neck (Experiment 2). In the context of the multisensory control of balance, these results suggest an increased reliance on vestibular and neck somatosensory information for controlling posture during quiet standing in condition of altered ankle neuromuscular function

A model for decoherence of entangled beauty

In the context of the entangled $B^0 \bar B^0$ state produced at the $\Upsilon(4S)$ resonance, we consider a modification of the usual quantum-mechanical time evolution with a dissipative term, which contains only one parameter denoted by $\lambda$ and respects complete positivity. In this way a decoherence effect is introduced in the time evolution of the 2-particle $B^0 \bar B^0$ state, which becomes stronger with increasing distance between the two particles. While our model of time evolution has decoherence for the 2-particle system, we assume that, after the decay of one of the two B mesons, the resulting 1-particle state obeys the purely quantum-mechanical time evolution. From the data on dilepton events we derive an upper bound on $\lambda$. We also show how $\lambda$ is related to the so-called ``decoherence parameter'' $\zeta$, which parameterizes decoherence in neutral flavoured meson--antimeson systems.Comment: 11 pages, revtex. Two references and some comments added, version to be published in Phys. Rev.

On the possibility of magneto-structural correlations: detailed studies of di-nickel carboxylate complexes

A series of water-bridged dinickel complexes of the general formula [Ni&lt;sub&gt;2&lt;/sub&gt;(μ&lt;sub&gt;2&lt;/sub&gt;-OH&lt;sub&gt;2&lt;/sub&gt;)(μ2- O&lt;sub&gt;2&lt;/sub&gt;C&lt;sup&gt;t&lt;/sup&gt;Bu)&lt;sub&gt;2&lt;/sub&gt;(O&lt;sub&gt;2&lt;/sub&gt;C&lt;sup&gt;t&lt;/sup&gt;Bu)2(L)(L0)] (L = HO&lt;sub&gt;2&lt;/sub&gt;C&lt;sup&gt;t&lt;/sup&gt;Bu, L0 = HO&lt;sub&gt;2&lt;/sub&gt;C&lt;sup&gt;t&lt;/sup&gt;Bu (1), pyridine (2), 3-methylpyridine (4); L = L0 = pyridine (3), 3-methylpyridine (5)) has been synthesized and structurally characterized by X-ray crystallography. The magnetic properties have been probed by magnetometry and EPR spectroscopy, and detailed measurements show that the axial zero-field splitting, D, of the nickel(ii) ions is on the same order as the isotropic exchange interaction, J, between the nickel sites. The isotropic exchange interaction can be related to the angle between the nickel centers and the bridging water molecule, while the magnitude of D can be related to the coordination sphere at the nickel sites

Bell inequalities for entangled kaons and their unitary time evolution

We investigate Bell inequalities for neutral kaon systems from Phi resonance decay to test local realism versus quantum mechanics. We emphasize the unitary time evolution of the states, that means we also include all decay product states, in contrast to other authors. Only this guarantees the use of the complete Hilbert space. We develop a general formalism for Bell inequalities including both arbitrary "quasi spin" states and different times; finally we analyze Wigner-type inequalities. They contain an additional term, a correction function h, as compared to the spin 1/2 or photon case, which changes considerably the possibility of quantum mechanics to violate the Bell inequality. Examples for special "quasi spin" states are given, especially those which are sensitive to the CP parameters epsilon and epsilon'.Comment: REVTeX, 22 page

First Dark Matter Search Results from a Surface Run of the 10-L DMTPC Directional Dark Matter Detector

The Dark Matter Time Projection Chamber (DMTPC) is a low pressure (75 Torr CF4) 10 liter detector capable of measuring the vector direction of nuclear recoils with the goal of directional dark matter detection. In this paper we present the first dark matter limit from DMTPC. In an analysis window of 80-200 keV recoil energy, based on a 35.7 g-day exposure, we set a 90% C.L. upper limit on the spin-dependent WIMP-proton cross section of 2.0 x 10^{-33} cm^{2} for 115 GeV/c^2 dark matter particle mass.Comment: accepted for publication in Physics Letters

Nitrosocarbonyl Hetero-Diels–Alder Cycloaddition: A New Tool for Conjugation

It is demonstrated that nitrosocarbonyl hetero-Diels-Alder chemistry is an efficient and versatile reaction that can be applied in macromolecular synthesis. Polyethylene glycol functionalized with a hydroxamic acid moiety undergoes facile coupling with cyclopentadiene-terminated polystyrene, through a copper-catalyzed as well as thermal hetero-Diels-Alder reaction. The mild and orthogonal methods used to carry out this reaction make it an attractive method for the synthesis of block copolymers. The resulting block copolymers were analyzed and characterized using GPC and NMR. The product materials could be subjected to thermal retro [4 + 2] cycloaddition, allowing for the liberation of the individual polymer chains and subsequent recycling of the diene-terminated polymers. © 2014 American Chemical Society