Soft deformable self-propelled particles

In this work we investigate the collective behavior of self-propelled particles that deform due to local pairwise interactions. We demonstrate that this deformation alone can induce alignment of the velocity vectors. The onset of collective motion is analyzed. Applying a Gaussian-core repulsion between the particles, we find a transition to disordered non-collective motion under compression. We here explain that this reflects the reentrant fluid behavior of the general Gaussian-core model now applied to a self-propelled system. Truncating the Gaussian potential can lead to cluster crystallization or more disordered cluster states. For intermediate values of the Gaussian-core potential we for the first time observe laning for deformable self-propelled particles. Finally, without the core potential, but including orientational noise, we connect our description to the Vicsek approach for self-propelled particles with nematic alignment interactions.Comment: 6 pages, 7 figure

Thermal and Non-thermal Plasmas in the Galaxy Cluster 3C 129

We describe new Chandra spectroscopy data of the cluster which harbors the prototypical "head tail" radio galaxy 3C 129 and the weaker radio galaxy 3C 129.1. We combined the Chandra data with Very Large Array (VLA) radio data taken at 0.33, 5, and 8 GHz (archival data) and 1.4 GHz (new data). We also obtained new HI observations at the Dominion Radio Astrophysical Observatory (DRAO) to measure the neutral Hydrogen column density in the direction of the cluster with arcminute angular resolution. The Chandra observation reveals extended X-ray emission from the radio galaxy 3C 129.1 with a total luminosity of 1.5E+41 erg/s. The X-ray excess is resolved into an extended central source of ~2 arcsec (1 kpc) diameter and several point sources with an individual luminosity up to 2.1E+40 erg/s. In the case of the radio galaxy 3C 129, the Chandra observation shows, in addition to core and jet X-ray emission reported in an earlier paper, some evidence for extended, diffuse X-ray emission from a region east of the radio core. The 12 arcsec x 36 arcsec (6 kpc x 17 kpc) region lies "in front" of the radio core, in the same direction into which the radio galaxy is moving. We use the radio and X-ray data to study in detail the pressure balance between the non-thermal radio plasma and the thermal Intra Cluster Medium (ICM) along the tail of 3C 129 which extends over 15 arcmin (427 kpc). Depending on the assumed lower energy cutoff of the electron energy spectrum, the minimum pressure of the radio plasma lies a factor of between 10 and 40 below the ICM pressure for a large part of the tail. We discuss several possibilities to explain the apparent pressure mismatch.Comment: Accepted for publication in MNRAS. Refereed manuscript. 14 pages, 8 figures, additional panel of Fig. 3 shows asymmetric ICM distributio

Towards granular hydrodynamics in two-dimensions

We study steady-state properties of inelastic gases in two-dimensions in the presence of an energy source. We generalize previous hydrodynamic treatments to situations where high and low density regions coexist. The theoretical predictions compare well with numerical simulations in the nearly elastic limit. It is also seen that the system can achieve a nonequilibrium steady-state with asymmetric velocity distributions, and we discuss the conditions under which such situations occur.Comment: 8 pages, 9 figures, revtex, references added, also available from http://arnold.uchicago.edu/?ebn

Quark-Lepton Symmetry In Five Dimensions

We construct a complete five dimensional Quark-Lepton symmetric model, with all fields propagating in the bulk. The extra dimension forms an $S^1/Z_2\times Z_2'$ orbifold with the zero mode fermions corresponding to standard model quarks localised at one fixed point. Zero modes corresponding to left(right)-chiral leptons are localised at (near) the other fixed point. This localisation pattern is motivated by the symmetries of the model. Shifting the right-handed neutrinos and charged leptons slightly from the fixed point provides a new mechanism for understanding the absence of relations of the type $m_e=m_u$ or $m_e=m_d$ in Quark-Lepton symmetric models. Flavour changing neutral currents resulting from Kaluza Klein gluon exchange, which typically arise in the quark sector of split fermion models, are suppressed due to the localisation of quarks at one point. The separation of quarks and leptons in the compact extra dimension also acts to suppress the proton decay rate. This permits the extra dimension to be much larger than that obtained in a previous construct, with the bound $1/R\gtrsim30$ TeV obtained.Comment: 12 pages, references added to match published versio

Cell-Type Specific Changes in Glial Morphology and Glucocorticoid Expression During Stress and Aging in the Medial Prefrontal Cortex.

Repeated exposure to stressors is known to produce large-scale remodeling of neurons within the prefrontal cortex (PFC). Recent work suggests stress-related forms of structural plasticity can interact with aging to drive distinct patterns of pyramidal cell morphological changes. However, little is known about how other cellular components within PFC might be affected by these challenges. Here, we examined the effects of stress exposure and aging on medial prefrontal cortical glial subpopulations. Interestingly, we found no changes in glial morphology with stress exposure but a profound morphological change with aging. Furthermore, we found an upregulation of non-nuclear glucocorticoid receptors (GR) with aging, while nuclear levels remained largely unaffected. Both changes are selective for microglia, with no stress or aging effect found in astrocytes. Lastly, we show that the changes found within microglia inversely correlated with the density of dendritic spines on layer III pyramidal cells. These findings suggest microglia play a selective role in synaptic health within the aging brain

CP Violation in Supersymmetric Theories: stop2->stop1 H H, stop2->stop1 Z Z, stop2->stop1 W+ W-, stop2->stop1 Z H

We study the decays stop2->stop1 H H, stop2->stop1 Z Z, stop2->stop1 W+ W- and stop2->stop1 Z H, with an eye towards measuring the CP-violating supersymmetric parameters contained in these processes. We find that stop2->stop1 H H tends to have the largest CP asymmetry and width, and is perhaps the most favourable experimentally. These decays are sensitive primarily to phi_At, the phase of the trilinear coupling A_t.Comment: 15 pages, 3 figures. Comments added; figure changed. Analysis and conclusions unchange

Leptonic Flavor and CP Violation

We discuss how neutrino oscillation experiments can probe new sources of leptonic flavor and CP violation.Comment: 8 pages, latex, no figures. Invited talk given at KAON 2001, Pisa, Italy, June 12 - 17, 200

Sneutrino-Antisneutrino Mixing and Neutrino Mass in Anomaly--mediated Supersymmetry Breaking Scenario

In supersymmetric models with nonzero Majorana neutrino mass, the sneutrino and antisneutrino mix, which may lead to same sign dilepton signals in future collider experiments. We point out that the anomaly-mediated supersymmetry breaking scenario has a good potential to provide an observable rate of such signals for the neutrino masses suggested by the atmospheric and solar neutrino oscillations. The sneutrino mixing rate is naturally enhanced by m_{3/2}/m_{\tilde{\nu}}={\cal O}(4\pi/\alpha) while the sneutrino decay rate is small enough on a sizable portion of the parameter space. We point out also that the sneutrino-antisneutrino mixing can provide much stronger information on some combinations of the neutrino masses and mixing angles than neutrino experiments.Comment: Revtex, 13 pages, 2 figure