| Tuesday, September 24, 2019 |
| Listening for Invisible Axions with Gravitational Waves | |
| Ben Stefanek, JGU Mainz | |
| Event Type: Informal HEP Talk | |
| Time: 9:55 AM - 10:55 AM | |
| Location: 726 Broadway, 940, CCPP Seminar | |
| Abstract: Conventional approaches to probing axions and axion-like particles (ALPs) typically rely on a coupling to photons. However, if this coupling is extremely weak, ALPs become invisible and are effectively decoupled from the Standard Model. Here we show that such invisible axions, which are viable candidates for dark matter, can produce a stochastic gravitational wave background in the early universe. This signal is generated in models where the invisible axion couples to a dark gauge boson that experiences a tachyonic instability when the axion begins to oscillate. Incidentally, the same mechanism also widens the viable parameter space for axion dark matter. Quantum fluctuations amplified by the exponentially growing gauge boson modes source chiral gravitational waves. For large axion decay constants, this signal is detectable by either pulsar timing arrays or space/ground-based gravitational wave detectors for a broad range of axion masses, thus providing a new window to probe invisible axion models. | |
| Formation and evolution of primordial black hole binaries | |
| Ville Vaskonen, King's College London | |
| Event Type: Informal Astro Talk | |
| Time: 11:00 AM - 11:30 AM | |
| Location: 726 Broadway, 902, Lg Conf | |
| Abstract: The observations of gravitational waves from black hole mergers by LIGO/Virgo has revived the interest in the possibility of primordial black hole (PBH) dark matter. In this talk I will describe how PBH binaries are formed in the early universe and discuss their survival until they merge. I will then use the merger rate estimates and the LIGO/Virgo observations to put constraints on the PBH abundance. In particular, I will show that the LIGO/Virgo observations exclude the possibility that more than O(1%) of dark matter consists of O(10M_sun) PBHs. | |
| Relativistic outflows in Neutron star mergers | |
| Ore Gottleib, Tel Aviv | |
| Event Type: Astro Seminar | |
| Time: 2:00 PM - 3:15 PM | |
| Location: 726 Broadway, 940, CCPP Seminar | |
| Abstract: Following a double Neutron star merger a relativistic jet propagates and interacts with the outflowing ejecta that surrounds the merger. As a result, matter is pushed around the jet to form a hot cocoon which applies pressure on the jet and potentially collimates it. After the jet breaks out from the merger ejecta, the cocoon expands and emits radiation over large angles throughout the entire electromagnetic spectrum. I will first discuss the evolution of the jet-cocoon system inside the ejecta and its effect on the morphology and emission from the outflow. Then I will present the different emission mechanisms of the jet+cocoon system, from the first seconds to years later, and how they compare with the set of observables in GW170817. I will conclude with what we expect from future events and what the jet-cocoon emission can tell us about Neutron star mergers and beyond. | |