Is the Polarized Antiquark Sea in the Nucleon Flavor Symmetric?

We show that the model which naturally explains the $\bar u \ne \bar d$ asymmetry in the nucleon and is in quantitative agreement with the Gottfried sum rule data, also predicts that in the proton $\Delta \bar u > 0 > \Delta \bar s > \Delta \bar d$ and $\Delta \bar u - \Delta \bar d > \bar d - \bar u > 0$. At the input scale, these results can be derived even analytically. Thus the violation of the flavor symmetry is more serious in the polarized case than in the unpolarized case. In contrast, many recent analyses of the polarized data have made a simplifying assumption that all the three $\Delta \bar q$'s have the same sign and magnitude. We point out the need to redo these analyses, allowing for the alternate scenario as described above. We present predictions of the model for the $W^-$ asymmetry in polarized $pp$ scattering, which can be tested at RHIC; these are quite different from those available in the literature.Comment: Talk given at the International Conference on Quark-Nuclear Physics (QNP2000), 21-25 Feb. 2000, CSSM, University of Adelaide, Australia. v2: refs added, discussion enlarged, conclusions unchanged. A short version has appeared in NP(A) proceedings. This (long) version is to appear in PR(C). Tables of polarized and unpolarized PDFs can be obtained by writing to the Autho

Aspects of causal viscous hydrodynamics

We investigate the phenomenology of freely expanding fluids, with different material properties, evolving through the Israel-Stewart (IS) causal viscous hydrodynamics, and compare our results with those obtained in the relativistic Eckart-Landau-Navier-Stokes (ELNS) acausal viscous hydrodynamics. Through the analysis of scaling invariants we give a definition of thermalization time which can be self-consistently determined in viscous hydrodynamics. Next we construct the solutions for one-dimensional boost-invariant flows. Expansion of viscous fluids is slower than that of one-dimensional ideal fluids, resulting in entropy production. At late times, these flows are reasonably well approximated by solutions obtained in ELNS hydrodynamics. Estimates of initial energy densities from observed final values are strongly dependent on the dynamics one chooses. For the same material, and the same final state, IS hydrodynamics gives the smallest initial energy density. We also study fluctuations about these one-dimensional boost-invariant backgrounds; they are damped in ELNS hydrodynamics but can become sound waves in IS hydrodynamics. The difference is obvious in power spectra due to clear signals of wave-interference in IS hydrodynamics, which is completely absent in ELNS dynamics.Comment: 27 pages, 17 figures, references added, minor changes, version to appear in Phys. Rev. (C

Haldane Exclusion Statistics and the Boltzmann Equation

We generalize the collision term in the one-dimensional Boltzmann-Nordheim transport equation for quasiparticles that obey the Haldane exclusion statistics. For the equilibrium situation, this leads to the ``golden rule'' factor for quantum transitions. As an application of this, we calculate the density response function of a one-dimensional electron gas in a periodic potential, assuming that the particle-hole excitations are quasiparticles obeying the new statistics. We also calculate the relaxation time of a nuclear spin in a metal using the modified golden rule.Comment: version accepted for publication in J. of Stat. Phy

Parton gas model for the nucleon structure functions

A phenomenological model for the nucleon structure functions is presented. Visualising the nucleon as a cavity filled with parton gas in thermal equilibrium and parametrizing the effects due to the finiteness of the nucleon volume, we obtain a good fit to the data on the unpolarized nucleon structure functions

Calcium-rich gap transients in the remote outskirts of galaxies

From the first two seasons of the Palomar Transient Factory, we identify three peculiar transients (PTF09dav, PTF10iuv, PTF11bij) with five distinguishing characteristics: peak luminosity in the gap between novae and supernovae (M_R ≈ - 15.5 to -16.5), rapid photometric evolution (t_(rise) ≈12-15 days), large photospheric velocities (≈6000 to 11000 km s^(-1)), early spectroscopic evolution into nebular phase (≈1 to 3 months) and peculiar nebular spectra dominated by Calcium. We also culled the extensive decade-long Lick Observatory Supernova Search database and identified an additional member of this group, SN 2007ke. Our choice of photometric and spectroscopic properties was motivated by SN 2005E (Perets et al. 2010). To our surprise, as in the case of SN 2005E, all four members of this group are also clearly offset from the bulk of their host galaxy. Given the well-sampled early and late-time light curves, we derive ejecta masses in the range of 0.4--0.7 M_⊙. Spectroscopically, we find that there may be a diversity in the photospheric phase, but the commonality is in the unusual nebular spectra. Our extensive follow-up observations rule out standard thermonuclear and standard core-collapse explosions for this class of "Calcium-rich gap" transients. If the progenitor is a white dwarf, we are likely seeing a detonation of the white dwarf core and perhaps, even shock-front interaction with a previously ejected nova shell. In the less likely scenario of a massive star progenitor, a very non-standard channel specific to a low-metallicity environment needs to be invoked (e.g., ejecta fallback leading to black hole formation). Detection (or lack thereof) of a faint underlying host (dwarf galaxy, cluster) will provide a crucial and decisive diagnostic to choose between these alternatives