20 November 2009

Title: Searching for Intermediate-Duration Gravitational-Wave Transients with LIGO
Speaker: Eric Thrane , University of Minnesotta
Time: 1:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481
Abstract: Gravitational-waves (GWs) are thought to originate from a variety of sources including supernovae, coalescing binary systems and rapidly spinning neutron stars. Some sources, such as pulsars, are thought to emit GWs continuously whereas other sources, such as supernovae, are expected to emit sub-second GW bursts. In this talk I'll discuss the possibility of intermediate-duration GW sources-- lasting hundreds of seconds to weeks. Specifically, I'll address microquasars, SGRs, pulsar glitches and long GRBs. I'll describe work on an "intermediate pipeline" that is being developed in order to facilitate searches for intermediate-duration transients using ground- based laser interferometers.

13 November 2009

Title: Primordial Gravitational Waves and the CMB
Speaker: Scott Dodelson, University of Chicago
Time: 1:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481
Abstract: Observations of the cosmic microwave background (CMB) offer strong, albeit indirect, evidence for an epoch of early dark energy, or inflation. Upcoming experiments can go further and detect the gravitational waves produced during this period, thereby pinning down the physics of inflation. I outline the current evidence for inflation, future prospects for learning about physics at ultra-high energy scales, and ancillary science that comes for free when experiments measure detailed properties of the CMB.

6 November 2009

Title: Role of PN approximations in EMRI calculations
Speaker: Bernard Whiting, University of Florida
Time: 1:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481
Abstract: Over the last decade, the self-force framework has been developed to the point where wave-form calculations are finally becoming possible. The first of these is likely to be comparable in scope to the first waveforms of gravitational collapse from Numerical Relativity, characterizing the final merger and ring-down. In the long run, self-force calculations alone are not likely to get us the 10^5 orbits we would want for use with LISA. Thus, a combination of numerical and semi-analytical methods is likely to be employed to make maximum use of our numerical capability. We have begun to make the first steps in integrating self-force and post-Newtonian calculations into a comprehensive framework for this purpose. In the course of these first steps, we have been able to encourage our post-Newtonian colleagues to push certain parts of their calculations in a direction which capitalizes on the potential which exists for making comparisons between their work and ours. I will comment on the current state of progress, and on other methods which are being employed for a similar purpose.

30 October 2009

Title: Black-hole binary coalescence: phenomenological models for non-precessing systems and astrophysics of intermediate-mass binaries
Speaker: Lucia Santamaria, AEI, Potsdam
Time: 1:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481
Abstract: Binaries of black holes (BBHs) are amongst the most interesting sources of gravitational radiation for current and future ground-based observatories. Theoretical models of the radiation produced by coalescing BBH systems that undergo an inspiraling process to eventually merge and ring down to a final Kerr black hole are of capital importance for current matched-filter searches of compact binaries in the output of the LIGO and Virgo detectors. The success of numerical relativity techniques to model the BBH merger and ringdown, together with the latest developments in post-Newtonian theory now allow the construction of reliable waveforms for the full BBH coalescence. I present a new phenomenological waveform model for non-precessing spinning BBHs with moderate mass ratios, based on matching post-Newtonian and numerical data in the frequency domain. This model can be immediately ported to LIGO/Virgo data analysis pipelines as a new approximant for injections or filtering templates. I also discuss the possibility of using this waveform model to search for intermediate-mass BBHs with current and future ground-based detectors.

23 October 2009

Title: Gravitational Waves from Cosmological Sources
Speaker: Xavier Siemens, UWM
Time: 1:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481
Abstract: In this talk I will review recent work and give details for plans for future work in the area of gravitational waves and cosmology by our group. I will focus on the gravitational waves produced by a network of cosmic strings and the bounds that can be placed on cosmic string model parameters using current and future experiments. I will also talk about recent work on gravitational waves produced by sources in the early universe when the expansion of the universe cannot be neglected. As an example of such a process I will consider the preheating epoch that may follow inflation and phase transitions. I will talk about prospects for detecting such signals using gravitational wave interferometers and pulsar timing arrays.

16 October 2009

Title: A Cross-Correlation Technique to Search for Periodic Gravitational Waves
Speaker: John Whelan , RIT
Time: 1:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481
Abstract: Cross-correlation of gravitational-wave (GW) data streams has been used to search for stochastic backgrounds, and the same technique was applied to look for periodic GWs from the low-mass X-ray binary (LMXB) Sco X-1. Recently a technique was developed which refines the cross-correlation scheme to take full advantage of the signal model for periodic gravitational waves from rotating neutron stars. By varying the time window over which data streams are correlated, the search can "trade off" between parameter sensitivity and computational cost. I describe this cross-corrlation method and potential applications to search LIGO and Virgo data for periodic GWs from systems with partially-known parameters, such as supernova remnants without an associated known pulsar, the center of the Milky Way Galaxy, and LMXBs.

2 October 2009

Title: Mother Guth: Investigating the progeny of false-vacuum bubbles
Speaker: Tom Linz, UWM
Time: 1:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481
Abstract: In order to investigate very early inflationary universe scenarios Guth, Guendelman, and Blau described the gravitational system of a spherical de Sitter space with a domain wall boundary surrounded by a true vacuum region ("Dynamics of false-vacuum bubbles" Phys. Rev. D. 35, 1747 (1987)). Recently, Dokuchaev and Chernov demonstrated how this system could be altered to investigate particle formation in the early universe, but their work hinges on an assumption relying on an intuition for a false-vacuum region. In our work, we demonstrate that the assumption is false, and that, in fact, the system is more complicated. We then show how this altered model could provide a powerful spring board for new investigations - from providing a new crucible for quantum cosmology to creating an altered model for inhomogeneous universes which could aid the investigation of galaxy formation in an expanding universe.

11 September 2009

Title: Reexamining the predictions of inflation for the CMB anisotropies
Speaker: Ivan Agullo, UWM
Time: 1:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481
Abstract: Inflationary cosmology has proved to be the most successful at predicting the properties of the anisotropies observed in the cosmic microwave background (CMB). In this talk we argue that quantum field renormalization can significantly influence the generation of primordial perturbations and hence the expected measurable imprint of cosmological inflation on the CMB. However, the new predictions remain in agreement with observation, and in fact favor the simplest forms of inflation. In the near future, observations of the influence of gravitational waves from the early universe on the CMB will test our new predictions.

14 August 2009

Title: Short Gamma Ray Bursts and Gravitational Wave Events
Speaker: Luigi Stella, Osservatorio Astronomico di Roma
Time: 1:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481

6 August 2009

Title: Bubbles in Eternal Inflation: A Classic(al) Effect
Speaker: John T. Giblin, Perimeter Institute
Time: 1:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481
Abstract: Cosmological bubble collisions arising from first order phase transitions are a generic consequence of the Eternal Inflation scenario. I will present our computational strategy for generating and evolving these bubbles in 3+1 dimensions and in a self- consistently expanding background. I will show the existence of classical field transitions--the classical nucleation of bubbles during collisions--which can dramatically alter the canonical description of eternal inflation.

19 June 2009

Title: The Search for Low Mass Compact Binary Coalescences in LIGO's S5 and Virgo's VSR1 Data
Speaker: Ruslan Vaulin, UWM
Time: 1:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481
Abstract: We report on the search for gravitational waves from coalescing compact binary systems with total mass from 2-35 Msun in the LIGO Fifth Science run (S5) data and Virgo's Science Run 1 (VSR1). We describe the pipeline employed by the LSC/Virgo to search for such waveforms in LIGO/Virgo data including how we suppress false signals originating from instrumental noise, how we evaluate the search efficiency for systems which may include spinning component objects, and how we establish confidence in likely detection candidates. Finally, we describe Bayesian coalescence rate upper limit calculations as a function of mass of the binary system and for several canonical mass systems including mass distributions representing binary neutron stars, binary black holes, and black hole neutron star binaries.

5 June 2009

Title: Binary neutron star inspiral and the equation of state
Speaker: Jocelyn Read, Max Planck Institute for Gravitational Physics, Postdam
Time: 1:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481
Abstract: The gravitational waveforms from the inspiral and merger of binary neutron stars are sensitive to the equation of state of neutron star matter, which is not well understood. Numerical simulations of binary neutron stars, including several orbits of inspiral, merger, and post-merger oscillations, show systematic differences as the equation of state is varied. For example, for most of the inspiral of a binary neutron star system the stars are well-modeled by point particles. However, as the neutron stars approach each other, an equation-of-state dependent tidal deformation modifies their orbits, changing the late inspiral waveform. These differences can give observable signatures in advanced gravitational-wave detectors. I will discuss estimates of the measurability of such changes based on both numerical simulations and on post-Newtonian calculations. I will also discuss the constraints that such measurements would place on the equation of state.

15 May 2009

Title: Constraining neutron star tidal Love numbers with gravitational wave detectors
Speaker: Tanja Hinderer, California Institute of Technology
Time: 1:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481
Abstract: Coalescing binary neutron stars are one of the most important sources for ground-based gravitational wave detectors. One of the key scientific goals of detecting the signal from such binaries is to obtain information about the nuclear equation of state, which is at present poorly constrained in the density range relevant to neutron star interiors. I will discuss the potential feasibility of obtaining robust constraints on the neutron star internal structure from gravitational wave observations with LIGO using data only from the early, low-frequency part of detected neutron star binary inspirals. In this adiabatic regime, the influence of a neutron star's internal structure is a small correction to the waveform's phase, but it is very clean and depends only on a single parameter of the star related to its tidal Love number, namely, the ratio of the induced quadrupole moment to the perturbing tidal field.

14 May 2009

Title: Exploring non-vacuum binaries: magnetic effects and neutrino emission
Speaker: Matt Anderson, Louisiana State University
Time: 2:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481
Abstract: Observational evidence suggests that sizeable magnetic fields are present in a fair number of neutron star binaries and neutron star-black hole binaries. These magnetic fields can have a strong influence on the fluid's dynamics, the energetics of the system and even the production of gravitational radiation. In addition to magnetic field effects, neutrino physics can also play an important role in binary neutron star mergers and in powering the disk wind in black hole--neutron star mergers. We present results of binary neutron star and black hole--neutron star collisions and examine the influence of magnetic fields on the gravitational waves, fluid structure and dynamical behavior of the system. We also present neutrino transport simulations of a cooling neutron star performed using general purpose programming on graphics processing units (GPGPU) and compare with known neutrino-leakage scheme results. We will present performance results comparing GPGPU versus CPU computing approaches.

17 Apr 2009

Title: Groping for a new renormalization scheme: scalar self-force in Schwarzschild spacetime
Speaker: Alan Wiseman, University of Wisconsin-Milwaukee
Time: 1:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481

10 Apr 2009

Title: Generalized symmetries and self-force.
Speaker: Abraham Harte, University of Chicago
Time: 1:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481
Abstract: This talk discusses a new formalism that uses generalized symmetry principles to greatly simplify self-force and self-torque problems for extended bodies. It leads to non-perturbative quasilocal expressions for the self-field's contribution to a body's effective linear and angular momenta. Another consequence is a simple proof of the Detweiler-Whiting axiom that sufficiently small objects only respond to a particular homogeneous component of their self-field (up to inertial effects). This is shown to be exact in some interesting cases. In others, standard results are recovered at lowest order. Beyond that, the details of a body's internal structure eventually become involved in an essential way.

27 Mar 2009

Title: Gravity Waves from Electroweak Phase Transition without Collider Traces
Speaker: Amjad Ashoorioon, University of Michigan
Time: 1:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481
Abstract: This talk discusses collider signals and the electroweak phase transition in a singlet extension of the Standard Model. We focus on the region in parameter space where the model develops no significant deviation in its low energy phenomenology from the Standard Model, nevertheless develops a strong phase transition. We conclude that even if the results of the upcoming generation of collider and low-energy probes are consistent with the Standard Model, the electroweak phase transition can be strong enough for electroweak baryogenesis or even production of gravitational radiation observable by the Big Bang Observer.

13 Mar 2009

Title: Physical derivation of the gravitational self-force and some applications
Speaker: Steve Detweiler, University of Florida
Time: 1:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481
Abstract: In General Relativity, the worldline of an object of infinitesimal size and mass is a geodesic of spacetime. Elementary Newtonian arguments show that an object of small, finite size might be accelerated by tidal effects which sum to yield a net force. Similarly, an object of small, finite mass is subject to the gravitational self-force but its world line surprisingly remains a geodesic. This result makes the self-force for gravitation much easier to understand than even the self-force for electricity and magnetism in flat spacetime. Effects of the gravitational self-force acting on a small mass in a circular orbit around a black hole have been compared to post-Newtonian analyses.

27 Feb 2009

Title: Iteration stability for simple stellar systems
Speaker: Charalampos Markakis, UWM
Time: 1:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481
Abstract: Similar methods have been used to construct models of isolated rotating stars and corotating or irrotational binaries, in Newtonian and relativistic contexts. The choice of method has been based on numerical experiments, which indicate that particular methods converge quickly to a solution, while others diverge. The theory underlying these differences, however, has not been understood. In an attempt to provide a better theoretical understanding, we analytically examine the behavior of different iterative schemes near an exact, spherically symmetric solution. We find the spectrum of the linearized iteration operator and show for self-consistent field methods that iterative instability corresponds to unstable modes of this operator. On the other hand, we show that the success of iteratively stable methods is due to (quasi-)nilpotency of this operator.

6 Feb 2009

Title: Phase-space structure of the Milky Way's dark halo
Speaker: Leanne D. Duffy, Los Alamos National Laboratory
Time: 1:00 PM (Meet for lunch at 12.30 PM)
Location: Physics 481
Abstract: The evolution of cold dark matter in phase-space inevitably leads to high density regions in physical space, known as caustics. The significance of these high density structures is a current topic of debate. One interesting possibility is presented by the caustic ring model, which describes the accretion of dark matter onto galactic halos. I explain the formation of dark matter caustics, present an overview of the caustic ring model and predictions of the model for the Milky Way halo. The resulting dark matter flows and overdensities may have important consequences for both direct and indirect dark matter detection experiments.

2 Jan 2009

Title: Pulsar timing near supermassive black holes: Schwarzschild holes and eclipsing orbits
Speaker: Teviet Creighton, University of Texas at Brownsville
Time: 1:00 PM (Meet for lunch at 12:30 PM)
Location: Physics 481
Abstract: If a pulsar orbits a supermassive black hole, the timing of pulses that pass close to the hole will show a variety of strong field effects. We analyze the case of Schwarzschild black holes using a straightforward formalism with two "universal functions" describing photon path bending and travel time in strong fields. In this first analysis we also consider only pulsar beams within the orbital plane. We find that multiple sets of pulses arrive at the detector from different trajectories around the hole, bearing distinctive amplitude and phase relationships. The phenomena and formalism should also apply to systems with more general orientations.