Direct searches for hidden photon dark matter in the particle mass range of 0.4-2070 neV (0.1-500 MHz).

Lunch Colloquium
Dr. Andrei P. Lobanov

Weakly interacting sub-eV particles (WISP) are steadily gaining more prominence as likely candidates for explaining the dark matter. The particular focus of attention is on the QCD axions, axion-like particles (ALP) with masses of 100neV-10 meV (corresponding to the frequency range of 24MHz-2.4 THz). In an even broader range of particle mass, non-thermally produced vector bosons (also termed "hidden photons") related to a broken U(1) gauge symmetry are also among the possible WISP dark matter candidates. at frequencies below ~30 GHz, resonant cavities can be effectively employed for direct searches of hidden photon (and other WISP) dark matter. The WISP Dark Matter eXperiment (WISPDMX) jointly run by the MPIfR and the University of Hamburg is the first direct hidden photon dark matter search probing the particle masses within the 0.8--2.07 ueV (208-500MHz) range with four resonant modes of a tunable radio frequency cavity and down to 0.4 neV (0.1 MHz) outside of resonance. In the first science run of WISPDMX, the dark matter signal was searched for in the 0.1-500 MHz frequency band sampled at a 50 Hz spectral resolution. A total of 22000 spectra were obtained during 10-second integrations made at each individual tuning step of the measurements. No dark matter signal is found, both in the individual spectra reaching minimum detectable power of 8e-19 W and in the averaged spectrum of all the measurements with the minimum detectable power of 5e-22 W attained for a total of 61 h of data taking. A plausible candidate signal at 0.90164783 ueV is still under investigation. The overall WISPDMX measurements provide the most stringent to date exclusion limits on the coupling constant of the hidden photon over the 70-2070 neV range of the particle mass. These results and prospects for further WISP dark matter searches in the 100neV-10 meV range will be discussed in this talk.

High-mass star and cluster formation in the Milky Way: the Herschel/HOBYS, IRAM/W43-HERO and ALMA-IMF view

Main Colloquium
Dr. Frédérique Motte
Institut de Planétologie et d'Astrophysique de Grenoble, France

The physical process by which stars inherit their properties, especially their mass, from those of their parental cloud is the fundamental issue that guides all star formation studies. Our knowledge of this legacy has profound implications for many areas of astrophysics, including the cosmic history of star formation in galaxies. The star-formation recipes commonly used, among which the origin of the initial mass function (IMF) and star formation rates (SFR), are considered to be universal and thus independent of galactic environments. Our studies challenge these recipes,which are related to our understanding of star formation. I will present the Herschel discovery of high-density cloud filaments, which are forming clusters of OB-type stars. Given their high star formation activity, these so-called mini-starburst clouds/ridges could be seen as "miniature and instant models" of starburst galaxies. The characteristics of mini-starburst ridges investigated with the NOEMA and ALMA interferometers challenge star formation models and shed light on the origin of massive clusters. In one of these ridges, the measured star formation rate (SFR) contradicts statistical models of star formation rates. Moreover, its measured core mass distribution suggests that the stellar initial mass function (IMF) may not be determined, in these extreme environments, at the prestellar stage. These results motivated the setting up of the ALMA-IMF Large Program, a project, whose source sample, main objectives and first results will be presented.