53385261
Supernovae Powered by Collapsar Accretion in Gamma-Ray Burst Sources
The association of long-duration gamma-ray bursts (LGRBs) with Type Ic supernovae presents a challenge to supernova explosion models. In the collapsar model for LGRBs, gamma rays are produced in an ultrarelativistic jet launching from the magnetosphere of the black hole that forms in the aftermath of the collapse of a rotating progenitor star. The jet is collimated along the star's rotation axis, but the concomitant luminous supernova should be relatively?though certainly not entirely?spherical, and should synthesize a substantial mass of 56Ni. Our goal is to provide a qualitative assessment of the possibility that accretion of the progenitor envelope onto the black hole, which powers the LGRB, could also deposit sufficient energy and nickel mass in the envelope to produce a luminous supernova. For this, the energy dissipated near the black hole during accretion must be transported outward, where it can drive a supernova-like shock wave. Here we suggest that the energy is transported by convection and develop an analytical toy model, relying on global mass and energy conservation, for the dynamics of stellar collapse. The model suggests that a ~10 000 km s?1 shock can be driven into the envelope and that ~1051 erg explosions are possible. The efficiency with which the accretion energy is being transferred to the envelope is governed by the competition of advection and convection at distances ~100-1000 km from the black hole and is sensitive to the values of the convective mixing length, the magnitude of the effective viscous stress, and the specific angular momentum of the infalling envelope. Substantial masses of 56Ni may be synthesized in the convective accretion flow over the course of tens of seconds from the initial circularization of the infalling envelope around the black hole. The synthesized nickel is convectively mixed with a much larger mass of unburned ejecta.
1102417
Properties of Gamma-Ray Burst Progenitor Stars
We determined some basic properties of stars that produce spectacular gamma-ray bursts at the end of their lives. We assumed that accretion of the outer portion of the stellar core by a central black hole fuels the prompt emission and that fall-back and accretion of the stellar envelope later produce the plateau in the x-ray light curve seen in some bursts. Using x-ray data for three bursts, we estimated the radius of the stellar core to be ∼(1 – 3) × 1010 cm and that of the stellar envelope to be ∼(1 – 2) × 1011 cm. The density profile in the envelope is fairly shallow, with ρ ∼ r–2 (where ρ is density and r is distance from the center of the explosion). The rotation speeds of the core and envelope are ∼0.05 and ∼0.2 of the local Keplerian speed, respectively.
14892076
Connecting (supersymmetry) CERN LHC measurements with high scale theories
If supersymmetry is discovered at the LHC, the measured spectrum of superpartner masses and couplings will allow us to probe the origins of supersymmetry breaking. However, to connect the collider-scale Lagrangian soft parameters to the more fundamental theory from which they arise, it is usually necessary to evolve them to higher scales. The apparent unification of gauge couplings restricts the possible forms of new physics above the electroweak scale, and suggests that such an extrapolation is possible. Even so, this task is complicated if the low-scale spectrum is not measured completely or precisely, or if there is new physics at heavy scales beyond the reach of collider experiments. In this work we study some of these obstacles to running up, and we investigate how to get around them. Our main conclusion is that even though such obstacles can make it very difficult to accurately determine the values of all the soft parameters at the high scale, there exist a number of special combinations of the soft parameters that can avoid these difficulties. We also present a systematic application of our techniques in an explicit example.
119290042
Origins of hidden sector dark matter II: collider physics
We consider a broad class of supersymmetric theories in which dark matter (DM) is the lightest superpartner (LSP) of a hidden sector that couples very weakly to visible sector fields. Portal interactions connecting visible and hidden sectors mediate the decay of the lightest observable superpartner (LOSP) into the LSP, allowing the LHC to function as a spectacular probe of the origin of hidden sector DM. As shown in a companion paper, this general two-sector framework allows only for a handful of DM production mechanisms, each of which maps to a distinctive window in lifetimes and cross-sections for the LOSP. In the present work we perform a systematic collider study of LOSP candidates and portal interactions, and for each case evaluate the prospects for successfully reconstructing the origin of DM at the LHC. If, for instance, DM arises from Freeze-Out and Decay, this may be verified if the LOSP is a bino or right-handed slepton decaying to the LSP through a variety of portal interactions, and with an annihilation cross-section within a narrow range. On the other hand, the Freeze-In mechanism may be verified for a complimentary set of LOSP candidates, and within a narrow range of LOSP lifetimes. In all cases, the LOSP is relatively long-lived on collider time scales, leading to events with displaced vertices. Furthermore, scenarios with a charged or colored LOSP are particularly promising.
119181202
Template banks to search for low-mass binary black holes in advanced gravitational-wave detectors
Coalescing binary black holes (BBHs) are among the most likely sources for the Laser Interferometer Gravitational-wave Observatory (LIGO) and its international partners Virgo and KAGRA. Optimal searches for BBHs require accurate waveforms for the signal model and effectual template banks that cover the mass space of interest. We investigate the ability of the second-order post-Newtonian TaylorF2 hexagonal template placement metric to construct an effectual template bank, if the template waveforms used are effective one body waveforms tuned to numerical relativity (EOBNRv2). We find that by combining the existing TaylorF2 placement metric with EOBNRv2 waveforms, we can construct an effectual search for BBHs with component masses in the range 3 Msolar = 2.68 radians, there is no significant loss in the total possible signal-to-noise ratio due to neglecting modes other than l = m = 2 in the template waveforms. For a source population uniformly distributed in spacial volume, over the entire sampled region of the component-mass space, the loss in detection rate (averaged over a uniform distribution of inclination angle and sky-location/polarization angles), remains below ~11%. For binaries with high mass-ratios \textit{and} 0.31 <= \iota <= 2.68, including higher order modes could increase the signal-to-noise ratio by as much as 8% in Advanced LIGO. Our results can be used to construct matched-filter searches in Advanced LIGO and Advanced Virgo.
118728848
On Geodesic Flows and Their Deformations in Bertrand Space-times
We study the energy conditions and geodesic deformations in Bertrand space-times. We show that these can be thought of as interesting physical space-times in certain regions of the underlying parameter space, where the weak and strong energy conditions hold. We further compute the ESR parameters and analyze them numerically. The focusing of radial time-like and radial null geodesics is shown explicitly, which verifies the Raychaudhuri equation.
119028722
Origins of hidden sector dark matter I: cosmology
We present a systematic cosmological study of a universe in which the visible sector is coupled, albeit very weakly, to a hidden sector comprised of its own set of particles and interactions. Assuming that dark matter (DM) resides in the hidden sector and is charged under a stabilizing symmetry shared by both sectors, we determine all possible origins of weak-scale DM allowed within this broad framework. We show that DM can arise only through a handful of mechanisms, lending particular focus to Freeze-Out and Decay and Freeze-In, as well as their variations involving late time re-annihilations of DM and DM particle anti-particle asymmetries. Much like standard Freeze-Out, where the abundance of DM depends only on the annihilation cross-section of the DM particle, these mechanisms depend only on a very small subset of physical parameters, many of which may be measured directly at the LHC. In particular, we show that each DM production mechanism is associated with a distinctive window in lifetimes and cross-sections for particles which may be produced in the near future. We evaluate prospects for employing the LHC to definitively reconstruct the origin of DM in a companion paper.