Michigan Center for Theoretical Physics

Ann Arbor, MI, United States

Michigan Center for Theoretical Physics

Ann Arbor, MI, United States
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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.


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.


Berlin A.,University of Chicago | Hooper D.,University of Chicago | Hooper D.,Fermi National Accelerator Laboratory | McDermott S.D.,Fermi National Accelerator Laboratory | McDermott S.D.,Michigan Center for Theoretical Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

Motivated by the gamma-ray excess observed from the region surrounding the Galactic Center, we explore particle dark matter models that could potentially account for the spectrum and normalization of this signal. Taking a model-independent approach, we consider an exhaustive list of tree-level diagrams for dark matter annihilation, and determine which could account for the observed gamma-ray emission while simultaneously predicting a thermal relic abundance equal to the measured cosmological dark matter density. We identify a wide variety of models that can meet these criteria without conflicting with existing constraints from direct detection experiments or the Large Hadron Collider (LHC). The prospects for detection in near future dark matter experiments and/or the upcoming 14 TeV LHC appear quite promising. © 2014 American Physical Society.


Berlin A.,University of Chicago | Gratia P.,University of Chicago | Hooper D.,Fermi National Accelerator Laboratory | Hooper D.,University of Chicago | And 2 more authors.
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

The gamma-ray excess observed from the Galactic Center can be interpreted as dark matter particles annihilating into standard model fermions with a cross section near that expected for a thermal relic. Although many particle physics models have been shown to be able to account for this signal, the fact that this particle has not yet been observed in direct detection experiments somewhat restricts the nature of its interactions. One way to suppress the dark matter's elastic scattering cross section with nuclei is to consider models in which the dark matter is part of a hidden sector. In such models, the dark matter can annihilate into other hidden sector particles, which then decay into standard model fermions through a small degree of mixing with the photon, Z, or Higgs bosons. After discussing the gamma-ray signal from hidden sector dark matter in general terms, we consider two concrete realizations: a hidden photon model in which the dark matter annihilates into a pair of vector gauge bosons that decay through kinetic mixing with the photon, and a scenario within the generalized next-to-minimal supersymmetric standard model in which the dark matter is a singlino-like neutralino that annihilates into a pair of singlet Higgs bosons, which decay through their mixing with the Higgs bosons of the minimal supersymmetric standard model. © 2014 American Physical Society.


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.


Kearney J.,Michigan Center for Theoretical Physics | Pierce A.,Michigan Center for Theoretical Physics | Thaler J.,Massachusetts Institute of Technology
Journal of High Energy Physics | Year: 2013

Natural theories of the weak scale often include fermionic partners of the top quark. If the electroweak symmetry breaking sector contains scalars beyond a single Higgs doublet, then top partners can have sizable branching ratios to these extended Higgs sector states. In fact, top partner decays may provide the most promising discovery mode for such scalars, especially given the large backgrounds to direct and associated production. In this paper, we present a search strategy for top partner decays to a charged Higgs boson and a bottom quark, focusing on the case where the charged Higgs dominantly decays to third-generation quarks to yield a multi-b final state. We also discuss ways to extend this search to exotic neutral scalars decaying to bottom quark pairs. © 2013 SISSA, Trieste, Italy.


Park M.,Michigan Center for Theoretical Physics | Zurek K.M.,Michigan Center for Theoretical Physics | Watson S.,Michigan Center for Theoretical Physics | Watson S.,Syracuse University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

We present a unified framework for the study of late time cosmic acceleration. Using methods of effective field theory, we show that existing proposals for late time acceleration can be subsumed in a single framework, rather than many compartmentalized theories. We construct the most general action consistent with symmetry principles, derive the background and perturbation evolution equations, and demonstrate that for special choices of our parameters we can reproduce results already existing in the literature. Lastly, we lay the foundation for future work placing phenomenological constraints on the parameters of the effective theory. Although in this paper we focus on late time acceleration, our construction also generalizes the effective field theory of inflation to the scalar-tensor and multifield case for perturbatively constructed backgrounds. © 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..


Ware J.,Michigan Center for Theoretical Physics | Saotome R.,Michigan Center for Theoretical Physics | Akhoury R.,Michigan Center for Theoretical Physics
Journal of High Energy Physics | Year: 2013

The infrared behavior of perturbative quantum gravity is studied using the method developed for QED by Faddeev and Kulish. The operator describing the asymptotic dynamics is derived and used to construct an IR-finite S matrix and space of asymptotic states. All-orders cancellation of IR divergences is shown explicitly at the level of matrix elements for the example case of gravitational potential scattering. As a practical appli- cation of the formalism, the soft part of a scalar scattering amplitude is related to the gravitational Wilson line and computed to all orders. © SISSA 2013.


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.

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