Cvetic M.,University of Pennsylvania |
Cvetic M.,University of Maribor |
Larsen F.,Michigan Center for Theoretical Physics
Journal of High Energy Physics | Year: 2012
We show that the warp factor of a generic asymptotically flat black hole in five dimensions can be adjusted such that a conformal symmetry emerges. The construction preserves all near horizon properties of the black holes, such as the thermodynamic potentials and the entropy. We interpret the geometry with modified asymptotic behavior as the "bare" black hole, with the ambient flat space removed. Our warp factor subtraction generalizes hidden conformal symmetry and applies whether or not rotation is significant. We also find a relation to standard AdS/CFT correspondence by embedding the black holes in six dimensions. The asymptotic conformal symmetry guarantees a dual CFT description of the general rotating black holes. © 2012 SISSA.
Dotti M.,Max Planck Institute for Astrophysics |
Ruszkowski M.,University of Michigan |
Ruszkowski M.,Michigan Center for Theoretical Physics
Astrophysical Journal Letters | Year: 2010
Several active galactic nuclei (AGNs) with multiple sets of emission lines (ELs) separated by over 2000 km s-1 have been observed recently. These have been interpreted as being due to massive black hole (MBH) recoil following a black hole merger, MBH binaries, or chance superpositions of AGNs in galaxy clusters. Moreover, a number of double-peaked AGNs with velocity offsets of ∼ a few 102 km s-1 have also been detected and interpreted as being due to the internal kinematics of the narrow-line regions or MBH binary systems. Here we re-examine the superposition model. Using the Millennium Run, we estimate the total number of detectable AGN pairs, and we set very conservative lower limits on the AGN superpositions as a function of the EL offset. We show that AGN pairs with high velocity line separations up to ∼ 2000 km s-1 are very likely to be chance superpositions of two AGNs in clusters of galaxies for reasonable assumptions about the relative fraction of AGNs. No superimposed AGN pairs are predicted for velocity offsets in excess of ∼ 3000 km s-1, as the required AGN fractions would violate observational constraints. The high velocity AGN pair numbers predicted here are competitive with those predicted from the models relying on MBH recoil or MBH binaries. However, the model fails to account for the largest EL velocity offsets that require the presence of MBH binaries. © 2010. The American Astronomical Society. All rights reserved.
Feldman D.,Michigan Center for Theoretical Physics |
Liu Z.,Cn Yang Institute For Theoretical Physics |
Nath P.,Northeastern University |
Peim G.,Northeastern University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010
Most analyses of dark matter within supersymmetry assume the entire cold dark matter arising only from weakly interacting neutralinos. We study a new class of models consisting of U(1)n hidden sector extensions of the minimal supersymmetric standard model that includes several stable particles, both fermionic and bosonic, which can be interpreted as constituents of dark matter. In one such class of models, dark matter is made up of both a Majorana dark matter particle, i.e., a neutralino, and a Dirac fermion with the current relic density of dark matter as given by WMAP being composed of the relic density of the two species. These models can explain the PAMELA positron data and are consistent with the antiproton flux data, as well as the photon data from FERMI-LAT. Further, it is shown that such models can also simultaneously produce spin-independent cross sections which can be probed in CDMS-II, XENON-100, and other ongoing dark matter experiments. The implications of the models at the LHC and at the next linear collider (NLC) are also briefly discussed. © 2010 The American Physical Society.
Zuhone J.A.,NASA |
Markevitch M.,NASA |
Ruszkowski M.,University of Michigan |
Ruszkowski M.,Michigan Center for Theoretical Physics |
Lee D.,University of Chicago
Astrophysical Journal | Year: 2013
Cold fronts in cluster cool cores should be erased on short timescales by thermal conduction, unless protected by magnetic fields that are "draped" parallel to the front surfaces, suppressing conduction perpendicular to the sloshing fronts. We present a series of MHD simulations of cold front formation in the core of a galaxy cluster with anisotropic thermal conduction, exploring a parameter space of conduction strengths parallel and perpendicular to the field lines. Including conduction has a strong effect on the temperature distribution of the core and the appearance of the cold fronts. Though magnetic field lines are draping parallel to the front surfaces, preventing conduction directly across them, the temperature jumps across the fronts are nevertheless reduced. The geometry of the field is such that the cold gas below the front surfaces can be connected to hotter regions outside via field lines along directions perpendicular to the plane of the sloshing motions and along sections of the front that are not perfectly draped. This results in the heating of this gas below the front on a timescale of a Gyr, but the sharpness of the density and temperature jumps may nevertheless be preserved. By modifying the gas density distribution below the front, conduction may indirectly aid in suppressing Kelvin-Helmholtz instabilities. If conduction along the field lines is unsuppressed, we find that the characteristic sharp jumps seen in Chandra observations of cold front clusters do not form. Therefore, the presence of cold fronts in hot clusters is in contradiction with our simulations with full Spitzer conduction. This suggests that the presence of cold fronts in hot clusters could be used to place upper limits on conduction in the bulk of the intracluster medium. Finally, the combination of sloshing and anisotropic thermal conduction can result in a larger flux of heat to the core than either process in isolation. While still not sufficient to prevent a cooling catastrophe in the very central (r 5 kpc) regions of the cool core (where something else is required, such as active galactic nucleus feedback), it reduces significantly the mass of gas that experiences a cooling catastrophe outside those small radii. © 2013. The American Astronomical Society. All rights reserved..
McDermott S.D.,Fermi National Accelerator Laboratory |
McDermott S.D.,Michigan Center for Theoretical Physics
Physics of the Dark Universe | Year: 2015
Dark matter particles annihilating into Standard Model fermions may be able to explain the recent observation of a gamma-ray excess in the direction of the Galactic Center. Recently, a hidden photon model has been proposed to explain this signal. Supplementing this model with a dipole moment operator and a small dark sector mass splitting allows a large cross section to a photon line while avoiding direct detection and other constraints. Comparing the line and continuum cross sections, we find that the line is suppressed only by the relative scales and couplings. Given current constraints on this ratio, a line discovery in the near future could point to a new scale Λ~O(1TeV), where we would expect to discover new charged particles. Moreover, such a line would also imply that dark matter can be visible in near-future direct detection experiments. (FERMILAB-PUB-14-205-A-T). © 2015 Elsevier B.V.