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Register a new userConstraints on Galactic Wino Densities from Gamma Ray Lines
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We systematically compute the annihilation rate for neutral winos into the final state gamma + X, including all leading radiative corrections. This includes both the Sommerfeld enhancement (in the decoupling limit for the Higgsino) and the resummation of the leading electroweak double logarithms. Adopting an analysis of the HESS experiment, we place constraints on the mass as a function of the wino fraction of the dark matter and the shape of the dark matter profile. We also determine how much coring is needed in the dark matter halo to make the wino a viable candidate as a function of its mass. Additionally, as part of our effective field theory formalism, we show that in the pure-Standard Model sector of our theory, emissions of soft Higgses are power-suppressed and that collinear Higgs emission does not contribute to leading double logs.
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Axion-like particles (ALPs) can oscillate to photons and vice versa in electromagnetic fields. The photon-ALP oscillation provides an attractive solution to the apparent transparency of the Universe to TeV photons. The allowed parameter regions for the ALP mass $m_{rm a}leq 10^{-7}$ eV have been tightly constrained by the Fermi-LAT and H.E.S.S observations of some extragalactic sources. In this work we show for the first time that the H.E.S.S observations of some TeV sources in the Galactic plane exclude the highest ALP mass region (i.e., $m_{rm a}sim {rm a ~fewtimes 10^{-7}}$ eV) that accounts for the TeV transparency of the Universe. The upcoming CTA observations of the Galactic TeV sources are shown to be able to improve the constraints significantly.
We consider the indirect detection of dark matter that is captured in the Sun and subsequently annihilates to long lived dark mediators. If these mediators escape the Sun before decaying, they can produce striking gamma ray signals, either via the decay of the mediators directly to photons, or via bremsstrahlung and hadronization of the mediator decay products. Using recent measurements from the HAWC Observatory, we determine model-independent limits on heavy dark matter that are orders of magnitude more powerful than direct detection experiments, for both spin-dependent and spin-independent scattering. We also consider a well-motivated model in which fermionic dark matter annihilates to dark photons. For such a realistic scenario, the strength of the solar gamma ray constraints are reduced, compared to the idealistic case, due to the fact that the dark matter capture cross section and mediator lifetime are related. Nonetheless, solar gamma ray constraints enable us to exclude a previously unconstrained region of dark photon parameter space.
We consider a simple extension of the type-II two-Higgs-doublet model by introducing a real scalar as a candidate for dark matter in the present Universe. The main annihilation mode of the dark matter particle with a mass of around $31-40$ GeV is into a $bbar{b}$ pair, and this annihilation mode suitably explains the observed excess of the gamma-ray flux from the Galactic Center. We identify the parameter region of the model that can fit the gamma-ray excess and satisfy phenomenological constraints, such as the observed dark matter relic density and the null results of direct dark matter search experiments. Most of the parameter region is found to be within the search reach of future direct dark matter detection experiments.
One aspect of the quantum nature of spacetime is its foaminess at very small scales. Many models for spacetime foam are defined by the accumulation power $alpha$, which parameterizes the rate at which Planck-scale spatial uncertainties (and thephase shifts they produce) may accumulate over large path-lengths. Here $alpha$ is defined by theexpression for the path-length fluctuations, $delta ell$, of a source at distance $ell$, wherein $delta ell simeq ell^{1 - alpha} ell_P^{alpha}$, with $ell_P$ being the Planck length. We reassess previous proposals to use astronomical observations ofdistant quasars and AGN to test models of spacetime foam. We show explicitly how wavefront distortions on small scales cause the image intensity to decay to the point where distant objects become undetectable when the path-length fluctuations become comparable to the wavelength of the radiation. We use X-ray observations from {em Chandra} to set the constraint $alpha gtrsim 0.58$, which rules out the random walk model (with $alpha = 1/2$). Much firmer constraints canbe set utilizing detections of quasars at GeV energies with {em Fermi}, and at TeV energies with ground-based Cherenkovtelescopes: $alpha gtrsim 0.67$ and $alpha gtrsim 0.72$, respectively. These limits on $alpha$ seem to rule out $alpha = 2/3$, the model of some physical interest.
We present new determinations of disk surface density, independent of an assumed dust opacity, for a sample of 7 bright, diverse protoplanetary disks using measurements of disk dust lines. We develop a robust method for determining the location of dust lines by modeling disk interferometric visibilities at multiple wavelengths. The disks in our sample have newly derived masses that are 9-27% of their host stellar mass, substantially larger than the minimum mass solar nebula. All are stable to gravitational collapse except for one which approaches the limit of Toomre-Q stability. Our mass estimates are 2-15 times larger than estimates from integrated optically thin dust emission. We derive depleted dust-to-gas ratios with typical values of ~$10^{-3}$ in the outer disk. Using coagulation models we derive dust surface density profiles that are consistent with millimeter dust observations. In these models, the disks formed with an initial dust mass that is a factor of ~10 greater than is presently observed. Of the three disks in our sample with resolved CO line emission, the masses of HD 163296, AS 209, and TW Hya are roughly 3, 115, and 40 times more massive than estimates from CO respectively. This range indicates that CO depletion is not uniform across different disks and that dust is a more robust tracer of total disk mass. Our method of determining surface density using dust lines is robust even if particles form as aggregates and is useful even in the presence of dust substructure caused by pressure traps. The low Toomre-Q values observed in this sample indicate that at least some disks do not accrete efficiently.
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