Current status of turbulent dynamo theory: From large-scale to small-scale dynamos

Several recent advances in turbulent dynamo theory are reviewed. High resolution simulations of small-scale and large-scale dynamo action in periodic domains are compared with each other and contrasted with similar results at low magnetic Prandtl numbers. It is argued that all the different cases show similarities at intermediate length scales. On the other hand, in the presence of helicity of the turbulence, power develops on large scales, which is not present in non-helical small-scale turbulent dynamos. At small length scales, differences occur in connection with the dissipation cutoff scales associated with the respective value of the magnetic Prandtl number. These differences are found to be independent of whether or not there is large-scale dynamo action. However, large-scale dynamos in homogeneous systems are shown to suffer from resistive slow-down even at intermediate length scales. The results from simulations are connected to mean field theory and its applications. Recent work on helicity fluxes to alleviate large-scale dynamo quenching, shear dynamos, nonlocal effects and magnetic structures from strong density stratification are highlighted. Several insights which arise from analytic considerations of small-scale dynamos are discussed.Comment: 36 pages, 11 figures, Spa. Sci. Rev., submitted to the special issue "Magnetism in the Universe" (ed. A. Balogh

A search for resonances decaying into a Higgs boson and a new particle X in the XH → qqbb final state with the ATLAS detector

A search for heavy resonances decaying into a Higgs boson (H) and a new particle (X) is reported, utilizing 36.1 fb−1 of proton–proton collision data at collected during 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. The particle X is assumed to decay to a pair of light quarks, and the fully hadronic final state is analysed. The search considers the regime of high XH resonance masses, where the X and H bosons are both highly Lorentz-boosted and are each reconstructed using a single jet with large radius parameter. A two-dimensional phase space of XH mass versus X mass is scanned for evidence of a signal, over a range of XH resonance mass values between 1 TeV and 4 TeV, and for X particles with masses from 50 GeV to 1000 GeV. All search results are consistent with the expectations for the background due to Standard Model processes, and 95% CL upper limits are set, as a function of XH and X masses, on the production cross-section of the resonance

Increased flux of HETE J1900.1-2455 detected with both Swift/XRT and RXTE/PCA

Following the non-detection of HETE J1900.1-2455 on June 6 (ATel #1098), we find this system considerably brighter in a ~5 ksec Swift/XRT observation performed on June 10, 2007 (2:25-12:14 UT). The X-ray spectrum can be well described by an absorbed powerlaw plus blackbody model, with Nh~0.19, kT~0.16 keV and a photon index of ~2.24. The inferred 2.0-10.0 keV flux is ~2.8E-10 erg/cm2/s, which corresponds to an X-ray luminosity ~8.4E35 (d/5kpc) erg/s

Swift/XRT non-detection of HETE J1900.1-2455

During a ~0.8 ksec pointed Swift/XRT observation performed on June 6, 2007 (18:26-21:38 UT), we did not detect the accreting millisecond pulsar HETE J1900.1-2455. We can set a 2-10 keV upper limit on the source flux of ~(5-15)E-14 erg/cm2/s (depending on the assumed spectral model). This is more than a factor of 10 weaker than the X-ray flux observed with Swift/XRT last week, on May 31 (ATEL #1091)