Implications of the Fermi-LAT diffuse gamma-ray measurements on annihilating or decaying Dark Matter

We analyze the recently published Fermi-LAT diffuse gamma-ray measurements in the context of leptonically annihilating or decaying dark matter (DM) with the aim to explain simultaneously the isotropic diffuse gamma-ray and the PAMELA, Fermi and HESS (PFH) anomalous $e^\pm$ data. Five different DM annihilation/decay channels $2e$, $2\mu$, $2\tau$, $4e$, or $4\mu$ (the latter two via an intermediate light particle $\phi$) are generated with PYTHIA. We calculate both the Galactic and extragalactic prompt and inverse Compton (IC) contributions to the resulting gamma-ray spectra. To find the Galactic IC spectra we use the interstellar radiation field model from the latest release of GALPROP. For the extragalactic signal we show that the amplitude of the prompt gamma-emission is very sensitive to the assumed model for the extragalactic background light. For our Galaxy we use the Einasto, NFW and Isothermal DM density profiles and include the effects of DM substructure assuming a simple subhalo model. Our calculations show that for the annihilating DM the extragalactic gamma-ray signal can dominate only if rather extreme power-law concentration-mass relation $C(M)$ is used, while more realistic $C(M)$ relations make the extragalactic component comparable or subdominant to the Galactic signal. For the decaying DM the Galactic signal always exceeds the extragalactic one. In the case of annihilating DM the PFH favored parameters can be ruled out only if power-law $C(M)$ relation is assumed. For DM decaying into $2\mu$ or $4\mu$ the PFH favored DM parameters are not in conflict with the Fermi gamma-ray data. We find that, due to the (almost) featureless Galactic IC spectrum and the DM halo substructure, annihilating DM may give a good simultaneous fit to the isotropic diffuse gamma-ray and to the PFH $e^\pm$ data without being in clear conflict with the other Fermi-LAT gamma-ray measurements.Comment: Accepted for publication in JCAP, added missing references, new Figs. 9 \& 10, 35 page

Multi-timescale Solar Cycles and the Possible Implications

Based on analysis of the annual averaged relative sunspot number (ASN) during 1700 -- 2009, 3 kinds of solar cycles are confirmed: the well-known 11-yr cycle (Schwabe cycle), 103-yr secular cycle (numbered as G1, G2, G3, and G4, respectively since 1700); and 51.5-yr Cycle. From similarities, an extrapolation of forthcoming solar cycles is made, and found that the solar cycle 24 will be a relative long and weak Schwabe cycle, which may reach to its apex around 2012-2014 in the vale between G3 and G4. Additionally, most Schwabe cycles are asymmetric with rapidly rising-phases and slowly decay-phases. The comparisons between ASN and the annual flare numbers with different GOES classes (C-class, M-class, X-class, and super-flare, here super-flare is defined as $\geq$ X10.0) and the annal averaged radio flux at frequency of 2.84 GHz indicate that solar flares have a tendency: the more powerful of the flare, the later it takes place after the onset of the Schwabe cycle, and most powerful flares take place in the decay phase of Schwabe cycle. Some discussions on the origin of solar cycles are presented.Comment: 8 pages, 4 figure

Magnetic Fields in the Milky Way

This chapter presents a review of observational studies to determine the magnetic field in the Milky Way, both in the disk and in the halo, focused on recent developments and on magnetic fields in the diffuse interstellar medium. I discuss some terminology which is confusingly or inconsistently used and try to summarize current status of our knowledge on magnetic field configurations and strengths in the Milky Way. Although many open questions still exist, more and more conclusions can be drawn on the large-scale and small-scale components of the Galactic magnetic field. The chapter is concluded with a brief outlook to observational projects in the near future.Comment: 22 pages, 5 figures, to appear in "Magnetic Fields in Diffuse Media", eds. E.M. de Gouveia Dal Pino and A. Lazaria

A Quantitative Model of Energy Release and Heating by Time-dependent, Localized Reconnection in a Flare with a Thermal Loop-top X-ray Source

We present a quantitative model of the magnetic energy stored and then released through magnetic reconnection for a flare on 26 Feb 2004. This flare, well observed by RHESSI and TRACE, shows evidence of non-thermal electrons only for a brief, early phase. Throughout the main period of energy release there is a super-hot (T>30 MK) plasma emitting thermal bremsstrahlung atop the flare loops. Our model describes the heating and compression of such a source by localized, transient magnetic reconnection. It is a three-dimensional generalization of the Petschek model whereby Alfven-speed retraction following reconnection drives supersonic inflows parallel to the field lines, which form shocks heating, compressing, and confining a loop-top plasma plug. The confining inflows provide longer life than a freely-expanding or conductively-cooling plasma of similar size and temperature. Superposition of successive transient episodes of localized reconnection across a current sheet produces an apparently persistent, localized source of high-temperature emission. The temperature of the source decreases smoothly on a time scale consistent with observations, far longer than the cooling time of a single plug. Built from a disordered collection of small plugs, the source need not have the coherent jet-like structure predicted by steady-state reconnection models. This new model predicts temperatures and emission measure consistent with the observations of 26 Feb 2004. Furthermore, the total energy released by the flare is found to be roughly consistent with that predicted by the model. Only a small fraction of the energy released appears in the super-hot source at any one time, but roughly a quarter of the flare energy is thermalized by the reconnection shocks over the course of the flare. All energy is presumed to ultimately appear in the lower-temperature T<20 MK, post-flare loops

Origins of the Ambient Solar Wind: Implications for Space Weather

The Sun's outer atmosphere is heated to temperatures of millions of degrees, and solar plasma flows out into interplanetary space at supersonic speeds. This paper reviews our current understanding of these interrelated problems: coronal heating and the acceleration of the ambient solar wind. We also discuss where the community stands in its ability to forecast how variations in the solar wind (i.e., fast and slow wind streams) impact the Earth. Although the last few decades have seen significant progress in observations and modeling, we still do not have a complete understanding of the relevant physical processes, nor do we have a quantitatively precise census of which coronal structures contribute to specific types of solar wind. Fast streams are known to be connected to the central regions of large coronal holes. Slow streams, however, appear to come from a wide range of sources, including streamers, pseudostreamers, coronal loops, active regions, and coronal hole boundaries. Complicating our understanding even more is the fact that processes such as turbulence, stream-stream interactions, and Coulomb collisions can make it difficult to unambiguously map a parcel measured at 1 AU back down to its coronal source. We also review recent progress -- in theoretical modeling, observational data analysis, and forecasting techniques that sit at the interface between data and theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue connected with a 2016 ISSI workshop on "The Scientific Foundations of Space Weather." 44 pages, 9 figure

Olber's Paradox for Superluminal Neutrinos: Constraining Extreme Neutrino Speeds at TeV-ZeV Energies with the Diffuse Neutrino Background

The only invariant speed in special relativity is c; therefore, if some neutrinos travel at even tiny speeds above c, normal special relativity is incomplete and any superluminal speed may be possible. I derive a limit on superluminal neutrino speeds v >> c at high energies by noting that such speeds would increase the size of the neutrino horizon. The increased volume of the Universe visible leads to a brighter astrophysical neutrino background. The nondetection of "guaranteed" neutrino backgrounds from star-forming galaxies and ultrahigh energy cosmic rays (UHECRs) constrains v/c at TeV--ZeV energies. I find that v/c <= 820 at 60 TeV from the nondetection of neutrinos from star-forming galaxies. The nondetection of neutrinos from UHECRs constrains v/c to be less than 2500 at 0.1 EeV in a pessimistic model and less than 4.6 at 4 EeV in an optimistic model. The UHECR neutrino background nondetection is strongly inconsistent with a naive quadratic extrapolation of the OPERA results to EeV energies. The limits apply subject to some caveats, particularly that the expected pionic neutrino backgrounds exist and that neutrinos travel faster than c when they pass the detector. They could be improved substantially as the expected neutrino backgrounds are better understood and with new experimental neutrino background limits. I also point out that extremely subluminal speeds would result in a much smaller neutrino background intensity than expected.Comment: 13 pages, 2 figures, fixed titl

Search for the glueball candidates f0(1500) and fJ(1710) in gamma gamma collisions

Data taken with the ALEPH detector at LEP1 have been used to search for gamma gamma production of the glueball candidates f0(1500) and fJ(1710) via their decay to pi+pi-. No signal is observed and upper limits to the product of gamma gamma width and pi+pi- branching ratio of the f0(1500) and the fJ(1710) have been measured to be Gamma_(gamma gamma -> f0(1500)). BR(f0(1500)->pi+pi-) < 0.31 keV and Gamma_(gamma gamma -> fJ(1710)). BR(fJ(1710)->pi+pi-) < 0.55 keV at 95% confidence level.Comment: 10 pages, 3 figure

Constraining Strong Baryon-Dark Matter Interactions with Primordial Nucleosynthesis and Cosmic Rays

Self-interacting dark matter (SIDM) was introduced by Spergel & Steinhardt to address possible discrepancies between collisionless dark matter simulations and observations on scales of less than 1 Mpc. We examine the case in which dark matter particles not only have strong self-interactions but also have strong interactions with baryons. The presence of such interactions will have direct implications for nuclear and particle astrophysics. Among these are a change in the predicted abundances from big bang nucleosynthesis (BBN) and the flux of gamma-rays produced by the decay of neutral pions which originate in collisions between dark matter and Galactic cosmic rays (CR). From these effects we constrain the strength of the baryon--dark matter interactions through the ratio of baryon - dark matter interaction cross section to dark matter mass, $s$. We find that BBN places a weak upper limit to this ratio $< 10^8 cm^2/g$. CR-SIDM interactions, however, limit the possible DM-baryon cross section to $< 5 \times 10^{-3} cm^2/g$; this rules out an energy-independent interaction, but not one which falls with center-of-mass velocity as $s \propto 1/v$ or steeper.Comment: 17 pages, 2 figures; plain LaTeX. To appear in PR

Search for supersymmetry with a dominant R-parity violating LQDbar couplings in e+e- collisions at centre-of-mass energies of 130GeV to 172 GeV

A search for pair-production of supersymmetric particles under the assumption that R-parity is violated via a dominant LQDbar coupling has been performed using the data collected by ALEPH at centre-of-mass energies of 130-172 GeV. The observed candidate events in the data are in agreement with the Standard Model expectation. This result is translated into lower limits on the masses of charginos, neutralinos, sleptons, sneutrinos and squarks. For instance, for m_0=500 GeV/c^2 and tan(beta)=sqrt(2) charginos with masses smaller than 81 GeV/c^2 and neutralinos with masses smaller than 29 GeV/c^2 are excluded at the 95% confidence level for any generation structure of the LQDbar coupling.Comment: 32 pages, 30 figure