Engineering topics

Hooper, Dan

Publications and source records attributed to Hooper, Dan.

133 records · Page 8

DOE OSTI2011

Dark Matter and Synchrotron Emission from Galactic Center Radio Filaments

The inner degrees of the Galactic center contain a large population of filamentary structures observed at radio frequencies. These so-called non-thermal radio filaments (NRFs) trace magnetic field lines and have attracted significant interest due to their hard (S_v ~ -0.1 +/- 0.4) synchrotron emission spectra. The origin of these filaments remains poorly understood. We show that the electrons and positrons created through the annihilations of a relatively light (~5-10 GeV) dark matter particle with the cross section predicted for a simple thermal relic can provide a compelling match to the intensity, spectral shape, and flux variation of the NRFs. Furthermore, the characteristics of the dark matter particle necessary to explain the synchrotron emission from the NRFs is consistent with those required to explain the excess gamma-ray emission observed from the Galactic center by the Fermi-LAT, as well as the direct detection signals observed by CoGeNT and DAMA/LIBRA.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2011

DARK MATTER AND SYNCHROTRON EMISSION FROM GALACTIC CENTER RADIO FILAMENTS

The inner degrees of the Galactic center contain a large population of filamentary structures observed at radio frequencies. These so-called non-thermal radio filaments (NRFs) trace magnetic field lines and have attracted significant interest due to their hard (S{sub v} {proportional_to}{nu}{sup -0.1{+-}0.4}) synchrotron emission spectra. The origin of these filaments remains poorly understood. We show that the electrons and positrons created through the annihilations of a relatively light ({approx}5-10 GeV) dark matter particle with the cross section predicted for a simple thermal relic can provide a compelling match to the intensity, spectral shape, and flux variation of the NRFs. Furthermore, the characteristics of the dark matter particle necessary to explain the synchrotron emission from the NRFs are consistent with those required to explain the excess {gamma}-ray emission observed from the Galactic center by the Fermi Large Area Telescope, as well as the direct detection signals observed by CoGeNT and DAMA/LIBRA.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2011

CoGeNT, DAMA, and Light Neutralino Dark Matter

Recent observations by the CoGeNT collaboration (as well as long standing observations by DAMA/LIBRA) suggest the presence of a ∼5–10 GeV dark matter particle with a somewhat large elastic scattering cross section with nucleons ( σ∼10−40 cm2 ). Within the context of the minimal supersymmetric standard model (MSSM), neutralinos in this mass range are not able to possess such large cross sections, and would be overproduced in the early universe. Simple extensions of the MSSM, however, can easily accommodate these observations. In particular, the extension of the MSSM by a chiral singlet superfield allows for the possibility that the dark matter is made up of a light singlino that interacts with nucleons largely through the exchange of a fairly light ( ∼30–70 GeV ) singlet-like scalar higgs, h1 . Such a scenario is consistent with all current collider constraints and can generate the signals reported by CoGeNT and DAMA/LIBRA. Furthermore, there is a generic limit of the extended model in which there is a singlet-like pseudoscalar higgs, a1 , with ma1∼mh1 and in which the χ0χ0 and bb¯ , ss¯ coupling magnitudes of the h1 and a1 are very similar. In this case, the thermal relic abundance is automatically consistent with the measured density of dark matter if mχ0 is sufficiently small that χ0χ0→bb¯ is forbidden.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2011

Implications of CoGeNT's new results for dark matter

The CoGeNT Collaboration has recently presented the results of their first 15 months of data, including the measurement of the spectrum of nuclear recoil candidate events, and the time variation of those events. These results appear consistent with the signal anticipated from a relatively light dark matter particle scattering elastically with nuclei. In this paper, we independently analyze the data set collected by CoGeNT and explore the implications of these results for dark matter. We find that the observed spectrum and rate is consistent with originating from dark matter particles with a mass in the range of 4.5-12 GeV and an elastic scattering cross section with nucleons of approximately {approx}10{sup -40} cm{sup 2}. We confirm the conclusion of the CoGeNT Collaboration that the data also includes a somewhat statistically significant (2.7{sigma}) indication of annual modulation, with a phase, period, and amplitude consistent with that predicted for dark matter. CoGeNT's phase is also consistent with the annual modulation reported by the DAMA/LIBRA Collaboration. We also discuss the null results reported by CDMS and XENON100, and comment on the prospects for other experiments to detect a dark matter particle with the properties implied by CoGeNT.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2011

A Leptophobic Z' And Dark Matter From Grand Unification

We explore the phenomenology of Grand Unified Models based on the E_6 group, focusing on the Z' with suppressed couplings to leptons that can appear in such models. We find that this Z' can accommodate the W+dijets anomaly reported by the CDF collaboration. Furthermore, a viable dark matter candidate in the form of a right-handed sneutrino is also present within the fundamental 27-dimensional representation of E_6. Through its sizable couplings to the Z', the dark matter is predicted to possess an elastic scattering cross section with neutrons which can generate the signals reported by the CoGeNT and DAMA/LIBRA collaborations. To avoid being overproduced in the early universe, the dark matter must annihilate to leptons through the exchange of charged or neutral fermions which appear in the 27 of E_6, providing an excellent fit to the gamma ray spectrum observed from the Galactic Center by the Fermi Gamma Ray Space Telescope.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2011

Dark Forces At The Tevatron

A simple explanation of the W + dijet excess recently reported by the CDF collaboration involves the introduction of a new gauge boson with sizable couplings to quarks, but with no or highly suppressed couplings to leptons. Anomaly-free theories which include such a leptophobic gauge boson must also include additional particle content, which may include a stable and otherwise viable candidate for dark matter. Based on the couplings and mass of the Z` required to generate the CDF excess, we predict such a dark matter candidate to possess an elastic scattering cross section with nucleons on the order of σ ~ 10 -40 cm 2 , providing a natural explanation for the signals reported by the CoGeNT and DAMA/LIBRA collaborations. In this light, CDF may be observing the gauge boson responsible for the force which mediates the interactions between the dark and visible matter of our universe.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2011

What the Tevatron Found?

The CDF collaboration has reported a 4.1{sigma} excess in their lepton, missing energy, and dijets channel. This excess, which takes the form of an approximately Gaussian peak centered at a dijet invariant mass of 147 GeV, has provoked a great deal of experimental and theoretical interest. Although the D0 collaboration has reported that they do not observe a signal consistent with CDF, there is currently no widely accepted explanation for the discrepancy between these two experiments. A resolution of this issue is of great importance - not least because it may teach us lessons relevant for future searches at the LHC - and it will clearly require additional information. In this paper, we consider the ability of the Tevatron and LHC detectors to observe evidence associated with the CDF excess in a variety of channels. We also discuss the ability of selected kinematic distributions to distinguish between Standard Model explanations of the observed excess and various new physics scenarios.

43 PARTICLE ACCELERATORS↗