Day 469

Saturday.

1307.4876
Weighting neutrinos in $f(R)$ gravity
He

Constrain the neutrino properties in f(R) gravity using the latest observations from CMB and BAO measurements.  First constrain separately the total mass of neutrinos and N_eff respectively; then constrain them simultaneously.  Find Sum m_nu < 0.462 eV at 95% CL for the combination of Planck, WMAP, BAO, ACT and SPT.  Also find N_eff-3.32+0.54-0.51 at 95% CL for the same data set.  When constraining N_eff and Sum m_nu simultaneously, the constraint is weaker.

1307.4985
Cosmological fast radio bursts from binary neutron star mergers
Totani

Fast radio bursts (FRBs) at cosmological distances recently discovered, whose duration is ~milliseconds.  Argue that the observed short duration is difficult to explain by giant flares of soft gamma-ray repeaters, though their event rate and energetics are consistent with FRBs.  Discuss NS-NS mergers as a possible origin of FRBs.  Considering uncertainties and cosmological rate evolution, the FRB rate is consistent with the plausible rate estimate of NS-NS mergers, while a large fraction of NS-NS mergers must produce observable FRBs.  A likely radiation mechanism is coherent radio emission like radio pulsars, by magnetic breaking when magnetic dipoles of neutron stars are synchronized to binary rotation [what does this mean?] at the time of coalescence.  B-fields of the standard strength (1e12 G) can explain the observed FRB fluxes, if the conversion efficiency from magnetic breaking energy loss to radio emission is similar to that of isolated radio pulsars.  Since FRBs tell us the exact time of mergers, correlated search [correlated search of what?] would significantly improve the effective sensitivity of gravitational wave detectors.

1307.4995
Primordial black holes in non-Gaussian regimes
Young, Byrnes

Primordial black holes (PBHs) can form in the early Universe from the collapse of rare, large density fluctuations.  They have never been observed, but this fact is enough to constrain the amplitude of fluctuations on very small scales which cannot be otherwise probed.  Because PBHs form only in very rare large fluctuations, the number of PBHs formed is extremely sensitive to changes in the shape of the tail of the fluctuation distribution - which depends on the amount of non-Gaussianity present.  First study how local non-Gaussianity of arbitrary size up to fifth order affects the abundance and constraints from PBHs, finding that they depend strongly on even small amounts of non-Gaussianity and the upper bound on the allowed amplitude of the PS can vary by several orders of magnitude.  The sign of the non-linearity parameters (f_NL, g_NL, etc) are particularly important.  Also study the abundance and constraints from PBHs in the curvaton scenario, in which case the complete NL probability distribution is known, and find that truncating to any given order (i.e., to order f_NL or g_NL, etc) does not give accurate results.

1307.5035
Preparing for an explosion: hydrodynamic instabilities and turbulence in presupernovae
Smith, Arnett

Both observations and direct numerical simulations are discordant with predictions of conventional stellar evolution cores for the latest stages of a massive star's life prior to core collapse.  Suggest that the problem lies in the treatment of turbulent convection in these codes, which ignores finite amplitude fluctuations in velocity and temperature, and their NL interaction with nuclear burning.  The hydrodynamic instabilities that may arise prompt us to discuss a number of far-reaching implications for the fates of massive stars.  In particular, explore connections to enhanced presupernova mass loss, unsteady nuclear burning and consequent eruptions, swelling of the stellar radius that may trigger violent interactions with a companion star, and potential modifications to the core structure that could dramatically impact calculations of the core-collpase mechanism itself.  These modifications may be of fundamental importance to the interpretation of young core-collapse supernova remnants.  They may also make possible the development of an early warning system for the detection of impending core collapse.

1307.5051
The effects of local primordial non-guassianity on the formation and evolution of galaxies
Zhao, Li, Shandera, Jeong

Numerical modeling of the NG signals from different inflation models is essential to correctly interpret current and near future data from large-scale structure surveys.  In this study, use high-resolution cosmo hydro sims to investigate the effects of primordial NG on the formation and evolution of galaxies from the cosmic dawn to the present day.  Focusing on the local type primordial NG, find that it may affect the formation history of stars and BHs in galaxies, and their distribution.  Compared to the Gaussian case, large non-G potential with f_NL>1e3 leads to earlier collapse of the first structures, more massive galaxies especially at high redshifts, stronger clustering of galaxies, and higher halo bias.  However, for smaller NG with f_NL<1e2, the effect is significantly weaker.  Observations of the distribution and properties of high-z, rare objects such as the first galaxies and quasars may provide further constraints on the primordial NG.