July 6, 2016 | 12:00 PM | ERC 401 Modeling the Propagation & Polarization of Gravitational Waves to Test GR Rhondale Tso, Caltech
To test General Relativity (GR) through gravitational wave (GW) detections the primary methods are: 1) modifying the source dynamics to account for corrections to GR, 2) modifying the propagation and dispersive properties of the GW. Often one can disentangle the latter from the former to investigate each independently. Our work looks at a new generic modification to the dispersion of GWs, irrespective of the source, to account for parametrized corrections to GR. This new model-independent approach encapsulates all previous studies and provides a roadmap for additional theories. In this talk the added features will be discussed, including frequency dependent dissipation, preferred space directions coupled to dissipation, and adjustments to the GW's polarization content during its time of flight. An overview of data analysis and potential pipeline implementation will be discussed.
July 6, 2016 | 2:00 PM | ERC 401 MHD description of chiral relativistic plasma Oleg Ruchayskiy, Niels Bohr Institute
In systems of relativistic particles, an electric current, parallel to the magnetic field, can flow. This phenomenon, known as "chiral magnetic effect", changes the dynamics of magnetized plasmas in an essential way. I will present proper equations of "chiral relativistic magnetohydrodynamics" and discuss their relevance for generation and evolution of cosmological magnetic fields in the electroweak epoch and for other relativistic systems.
September 15, 2016 | 1:00 PM | ERC 401 Understanding large-scale structure from the CMB Emmanuel Schaan, Princeton University
In this seminar, I will present two promising ways in which the cosmic microwave background (CMB) sheds light on critical uncertain physics and systematics of the large-scale structure. Shear calibration with CMB lensing (arXiv:1607.01761): Realizing the full potential of upcoming weak lensing surveys requires an exquisite understanding of the errors in galaxy shape estimation. In particular, such errors lead to a multiplicative bias in the shear, degenerate with the matter density parameter and the amplitude of fluctuations. Its redshift-evolution can hide the true evolution of the growth of structure, which probes dark energy and possible modifications to general relativity. I will show that CMB lensing from a stage 4 experiment (CMB S4) can self-calibrate the shear for an LSST-like optical lensing experiment. This holds in the presence of photo-z errors and intrinsic alignment. Evidence for the kinematic Sunyaev-Zel'dovich (kSZ) effect; cluster energetics (arXiv:1510.06442): Through the kSZ effect, the baryon momentum field is imprinted on the CMB. I will report significant evidence for the kSZ effect from ACTPol and peculiar velocities reconstructed from BOSS. I will present the prospects for constraining cluster gas profiles and energetics from the kSZ effect with SPT-3G, AdvACT and CMB S4. This will provide constraints for galaxy formation and feedback models.
June 27, 2016 | 12:00 PM | ERC 545 Detection of CH3CN in a Diffuse Cloud by Hot Axis Effect indicating its coexistence with C60+, a carrier of Diffuse Interstellar Bands Mitsunori Araki, Tokyo University of Science, Japan
Diffuse interstellar bands (DIBs) are optical absorption lines by molecules in diffuse cloud. Initially observed more than 100 years ago, they still remain the longest standing unsolved problem in spectroscopy and astrochemistry, although five DIBs have recently been identified as due to fullerene ion C60+. Identifications of DIBs are important because they can give us information for chemical composition in space. To identify carrier molecules of DIBs we have measured DIB candidate molecules produced in the laboratory to compare their absorption spectra with astronomically observed DIB spectra. In this talk, I first present our latest results on the search for the thiophenoxy radical C6H5S by using our cavity ringdown spectrometer. I then present a new insight into diffuse clouds. Molecules in diffuse clouds are collisionally heated and radiatively cooled. Due to the spectroscopic selection rules, acetonitrile CH3CN is cooled well for the end-over-end rotation but is not cooled for rotation around its molecular axis. We made a model of this peculiar rotation as "Hot Axis Effect." Based on this model, we estimated a rotational absorption spectrum of CH3CN in the radio frequency region. By using Nobeyama 45 m radio telescope, the absorption line was detected in the diffuse cloud in front of Orion molecular cloud. Absorption lines of the fullerene have also been reported in this diffuse cloud. Thus we found that CH3CN coexists with C60+ in this diffuse cloud.
July 18, 2016 | 2:00 PM | ERC 545 Radiation hydrodynamical models of the inner rim in protoplanetary disks Mario Flock, JPL/Caltech
Many stars host planets orbiting within one astronomical unit (AU). These close planets' origins are a mystery that motivates investigating protoplanetary disks' central regions. A key factor governing the conditions near the star is the silicate sublimation front, which largely determines where the starlight is absorbed, and which is often called the inner rim. We present the first radiation hydrodynamical modeling of the sublimation front in the disks around the young intermediate-mass stars called Herbig Ae stars. The models are axisymmetric, and include starlight heating, silicate grains sublimating and condensing to equilibrium at the local, time-dependent temperature and density, and accretion stresses parametrizing the results of MHD magneto rotational turbulence models. The results show for the first time the dynamical stability of the rim. Passing the model disks into Monte Carlo radiative transfer calculations allows us to directly compare with observational constraints. The inner rim has a substantial radial extent, corresponding to several disk scale heights. A pressure maximum develops at the position of thermal ionization at temperatures about 1000 K. The pressure maximum is capable of halting solid pebbles' radial drift and concentrating them in a zone where temperatures are sufficiently high for annealing to form crystalline silicates.