- The character "*" denotes a student talk; eligible for DGRAV's best student talk prize.
- All talks are 12+3 format (12 minutes of speaking, 3 minutes of questions).
- CCB = Charlton College of Business (location of the meeting).
- The public talk will take place in the Main Auditorium located at the Campus Center. This is a 1 minute walk from the EGM's main location. Participants can also drive to parking lot 5.

Time | |
---|---|

8:00 - 9:00 | Check-in and breakfast (CCB lobby) |

9:00 - 9:15 | Welcome remarks |

Talk | Abstract | |
---|---|---|

9:15 - 9:30 | Commutative diagrams for quantum cosmology, Matthew E. Hogan (Wells College) | In this talk, I will present recent work on the relationship between quantization and symmetry reduction, as applied to the field of quantum cosmology. Starting with classical general relativity, one has (at least) two options: one may symmetry-reduce the theory (by varying degrees), leading to the homogeneous-isotropic standard FLRW cosmological model (or its anisotropic Bianchi extensions), or one may try to apply (canonical) quantization directly, leading to the theory of (loop) quantum gravity (LQG). To reach quantum cosmology, however, there are again, now, (at least) two options: symmetry-reducing the theory of LQG (in an appropriate sense), or quantizing FLRW (or Bianchi) models, as is done in loop quantum cosmology (LQC). These two paths, however, do not necessarily commute; in my talk, I will present recent progress that we have made in resolving this issue, which involves both conceptual and technical considerations. |

9:30 - 9:45 | Numerical Approaches in Loop Quantum Cosmology, Direct Methods in the Schwarzschild Interior, Alec Yonika* (UMassD) | Loop Quantum Cosmology (LQC) models utilize evolution equations that take the form of finite difference (FD) or recursive formulas. Prior work on the Corichi-Singh model analyzed the characteristics of these FD expressions, yielding novel physical constraints in order to forbid unbounded (exponential) growth. We present work that confirms that such constraints are a fundamental physical feature of the Corichi-Singh model of the Schwarzschild interior and not a numerical artifact. While helping establishing the validity of the constraints, unique benefits of novel numerical methods in the field of LQC are observed. |

9:45 - 10:00 | Large Quantum Stress Tensor Fluctuations, Larry Ford (Tufts University) | This talk will review recent results on the probability distributions for spacetime averaged quantum stress tensor operators and their applications. These results indicate that measurements made in a finite time interval can lead to large quantum fluctuations which are described by these distributions. The physical implications include large passive quantum fluctuations of the gravitational field and enhanced rates for false vacuum decay. |

10:00 - 10:15 | Vacuum decay induced by quantum fluctuations, Haiyun Huang* (Tufts University) | The talk will discuss the vacuum decay process which are induced by quantum fluctuations. The standard instanton solution of the vacuum decay is analogous to the WKB approximation in quantum mechanics, giving the rate of vacuum decay through a 'tunneling process'. The fluctuation of the field can be seen as an effect of ‘kicking the field over the barrier’. If the fluctuation of averaged field time derivative is considered, the decay rate is comparable with the that given by tunneling; if the fluctuations come from the effect of averaged square of the field time derivative, the ‘flying over’ probability can dominate over the standard tunneling probability. |

10:15 - 10:30 | A Numerical Approach to Quantum Stress Tensor Fluctuations, Peter Wu* (Tufts University) | Recent calculations of the probability distributions for averaged stress tensor operators suggest that large fluctuations may be probable enough to have observable effects. These calculations deduce the tails of the distributions by looking at the dominant terms of the operators' high moments, a method that is unable to uniquely determine the functional forms. In this talk, we introduce an alternative, independent method for finding the probability distributions by means of numerical diagonalization, in an effort to verify the analytical results and better understand the finer details of these distributions. |

10:30 - 11:00 | Coffee Break (CCB lobby) | Coffee Break (CCB lobby) |

Talk | Abstract | |
---|---|---|

11:00 - 11:10 | ICERM's Advances in Computational Relativity: Q&A session | https://icerm.brown.edu/programs/sp-f20/ |

11:10 - 11:25 | Multi-waveform cross-correlation search method for intermediate-duration gravitational waves from gamma-ray bursts, Robert Coyne (University of Rhode Island) | Here we report on improvements to the Cross-Correlation Algorithm (CoCoA) (R.Coyne et. al., Phys Rev D.93104059 (2016)), which is a gravitational wave analysis pipeline designed to optimize searches for intermediate-duration (100−10,000s) gravitational waves (GWs) that may arise from e.g. post-binary merger remnants of gamma-ray bursts. The improvements extend previously simulated searches on idealized noise real data collected to those performed on real data from ground-based GW detectors. We further develop the detection statistics on which CoCoA is based to allow for multi-waveform searches spanning a physically-motivated parameter space, so as to account for uncertainties in the physical properties of GRB remnants. |

11:25 - 11:40 | Towards a new multipolar description of gravitational waves from binary black holes, Lionel London (MIT) | Since Einstein’s quadrupole formalism, multipolar analysis has played a central role in gravitational wave theory. In particular, gravitational waves from compact sources are ubiquitously represented using spin weighted spherical harmonic multipoles. But despite their ubiquity, there is reason to suspect that a more general perspective may point the way to new physical insights. In this talk I will review the recent developments in gravitational wave signal models for binary black hole systems. A key limitation of many such models is that they do not account for the more natural “spheroidal” harmonic nature of the post-merger signal. In this regard, I will briefly discuss recent work at the interface of BH perturbation theory, and numerical relativity which uses spheroidal harmonic information from NR simulations to model the late post-merger for spinning but non-precessing binary black hole systems. Lastly, I will introduce recent work which proposes the spheroidal harmonics as a potentially more appropriate basis for all of inspiral, merger and ringdown. |

11:40 - 11:55 | Impact of subdominant modes on the measurability of binary black hole spin parameters, Feroz Hussain Shaik* (UMassD) | Gravitational-wave Bayesian inference studies require a model to estimate parameter values. Most previous parameter estimation (PE) studies use models that neglect spherical harmonic modes beyond the dominant quadrupole one due to their unavailability. Recently, surrogate models built using numerical relativity (NR) data have been developed that are fast enough for PE studies, contain higher mode content, and cover a large portion of the relevant parameter space. These surrogates also contain the late inspiral, merger, and ringdown of the binary system, making them ideal for parameter estimation studies of heavy systems. In particular, we present results using a recently built aligned-spin surrogate model and a highly-parallelizable rapid inference algorithm. Using these NR-based surrogate models we performed a parameter estimation study to understand the effects of higher modes on spin measurability for both current and future gravitational-wave detectors. |

11:55 - 12:10 | Improving and testing a parameter estimation algorithm that directly compares numerical relativity waveforms to gravitational wave data, Jacob Lange* (RIT) | In previous work, we demonstrated and tested our method that allows us to directly compare Numerical Relativity (NR) waveforms to the gravitational wave (GW) data. In this project, we continue to test and develop different aspects of this method. We demonstrate via examples that we can hybridize the higher modes of aligned as well as precessing systems. We verify that our discrete NR grid has little to no affect on many sources in different parts of parameter space. To address any differences that remain, we develop and demonstrate an algorithm that uses the lnL distribution as well as the error in the fit used to generate said distribution to suggest new points to improve the fit. Using examples, we show how adding the suggested points influences the overall posterior distribution. |

12:10 - 1:15 | Lunch (CCB lobby and patio) | Lunch (CCB lobby and patio) |

Talk | Abstract | |
---|---|---|

1:15 - 1:30 | Multi-Messenger Measurements of Blackhole Spindown with Blackhole-Pulsar Binaries, Steven Liebling (Long Island University) | The development of new, large radio telescopes such as the SKA is expected to yield observations of blackhole-pulsar binaries which should be excellent probes of strong-field gravity. In particular, we argue that such systems can potentially shed light on processes associated with superradiance. |

1:30 - 1:45 | Black-hole accretion in the presence of Dark Matter heating, Elizabeth Bennewitz* (Bowdoin College) | We study the effects of heating by dark matter (DM) annihilation on black hole accretion. We observe that, for reasonable assumptions about DM densities in spikes around supermassive black holes as well as DM masses and annihilation cross-sections within the standard weakly interacting massive particle model, heating by DM annihilation may have an order unity effect on the accretion onto Sgr A∗ in the Galactic center. Motivated by this observation we study the effects of such heating on Bondi accretion, i.e. spherically symmetric, steady-state Newtonian accretion onto a black hole. We consider different adiabatic indices for the gas, and different power-law exponents for the dark- matter density profile. We find that typical transonic solutions with heating have a significantly reduced accretion rate. However, for many plausible parameters transonic solutions do not exist, suggesting a breakdown of the underlying assumptions of Bondi accretion. Our findings indicate that heating by DM annihilation may play an important role in the accretion onto supermassive black holes at the center of galaxies, and may help explain the low accretion rate observed for Sgr A∗. |

1:45 - 2:00 | Three Dimensional Dynamically Driven Double-Degenerate Double-Detonation Simulations for Type 1a Supernova, Vishal Tiwari* (UMassD) | Type Ia supernovae are thermonuclear explosions of white dwarfs, characterized by the nuclear burning of carbon and oxygen and serve as standardizable candles for cosmology. However, the exact nature of the progenitors and mechanisms of explosions is still a mystery. In recent years, the dynamically driven double-degenerate double-detonation (D6) model is gaining popularity. A D6 model is a setup of double degenerate progenitors where the primary and the secondary have thin layers of He on their surface. The accretion of the He onto the primary can lead to a He detonation on the surface, which would eventually lead to the detonation of carbon, thus leading to a type Ia supernova. In this work, we present a three-dimensional simulation of a D6 scenario where we see a surface detonation on the primaries surface, which travels across the star and collides at the other end. |

2:00 - 2:15 | Simulating Disks With Discontinous Galerkin Methods, Nils Deppe* (Cornell University) | We provide an update on the development of SpECTRE (https://github.com/sxs-collaboration/spectre), a new open-source relativistic astrophysics code that combines a discontinuous Galerkin method with a task-based parallelism model. SpECTRE's goal is to achieve more accurate solutions for challenging relativistic astrophysics problems such as core-collapse supernovae and binary neutron star mergers, while making efficient use of the largest supercomputers. We will discuss recent progress we've made on simulating disks with discontinuous Galerkin methods and the challenges that remain. We acknowledge support from NSF PHY-1606654 and the Sherman Fairchild Foundation. |

2:15 - 2:30 | Relativistic Dynamics in Black Hole Triples, Halston Lim* (MIT) | Binary black holes can be driven to merger by interactions with a third companion via the Lidov-Kozai mechanism. The impact of this mechanism may be observable by LIGO/Virgo through the production of binaries with distinct eccentricity. We present a direct method to derive the orbit averaged gravitational dynamics of a hierarchical three-body system to first post-Newtonian order. We start with the Einstein-Infeld-Hoffman (EIH) equations for a three-body system and write the accelerations as a power series in the ratio of the semi-major axes of the two orbits, (a1/a2). At zeroth order, the two orbits evolve independently. At first order, orbital interaction terms (of both Newtonian and relativistic nature) start to appear, and sub-leading interaction terms appear at higher powers in (v/c) and (a1/a2). These interaction terms become important when the three-body Newtonian timescales are comparable to the relativistic timescales and provide an analytic description of behavior observed in previous N-body simulations. |

2:30 - 2:45 | Oscillations of Fast Rotating Neutron Stars, Christian Krueger (University of New Hampshire-Durham) | TBD |

2:45 - 3:15 | Coffee Break (CCB lobby) | Coffee Break (CCB lobby) |

Talk | Abstract | |
---|---|---|

3:15 - 3:30 | Persistent gravitational wave observables, Alexander Grant* (Cornell University) | The gravitational wave memory effect is the permanent relative displacement of a pair of initially comoving test particles caused by the passage of a burst of gravitational waves. Recent research has clarified the physical origin and the interpretation of this effect in terms of conserved charges at null infinity and "soft theorems". In this talk, we describe a more general class of effects, not necessarily associated with those charges and soft theorems, that are, in principle, measurable. We shall refer to these effects as persistent gravitational wave observables. Like geodesic deviation in gravitational wave memory, these observables vanish in non-radiative regions of a spacetime, and their effects "persist" after a region of spacetime which is radiating. We give three examples of such persistent observables: (i) a generalization of geodesic deviation that allows for acceleration, (ii) a holonomy observable defined in terms of a closed loop that includes the relative velocity, proper time and accumulated relative rotation effects previously identified, as well as new effects, and (iii) an observable defined using using a spinning test particle. We briefly discuss the ability of gravitational wave detectors (such as LIGO) to measure these observables. |

3:30 - 3:45 | The interior of a binary black-hole merger, Daniel Pook-Kolb* (AEI Hannover, Germany) | Marginally outer trapped surfaces (MOTSs) are routinely used in numerical simulations of black-hole spacetimes. They are an invaluable tool for locating and characterizing black holes quasilocally in real time while the simulation is ongoing. However, there has been a gap in our understanding of the full binary black-hole merger in terms of MOTSs as these seem to appear and disappear unpredictably. In this talk I will first show that MOTSs are, in fact, well behaved and that their behavior is predictable and related to the stability operator. Using numerical simulations of binary black-hole head-on collisions, we have found strong numerical evidence for the existence of a connected sequence of MOTSs taking us from the two disjoint initial black-hole horizons to the final common horizon in such a merger. A key component is a new phenomenon: the merger of MOTSs in the interior of the newly formed common horizon. The fate of its inner branch, which has previously only been speculated about, is revealed using a new numerical method capable of finding even highly distorted non-star-shaped MOTSs. Finally, I will discuss how a connected history of MOTSs provides a new possibility to tackle an important problem of mathematical relativity, namely the Penrose inequality, in the case of generic astrophysical binary black-hole configurations. |

3:45 - 4:00 | An extended object passing through the Cauchy Horizon singularity, Caroline Mallory* (UMassD) | TBD |

4:00 - 4:15 | Geometry of Surface Tension, Howard Perko (Colorado State University) | This brief presentation will explore how to modify equations of general relativity to include surface tension. Surface tension appears as negative terms in the stress energy tensor derived not from chemistry, but from simple statistical thermodynamics of energetic hypersurfaces regardless of dimension. Tensors describing convective flow and rate of configuration of spacetime with surface tension will be presented. These tensors contain components mathematically similar to quantum mechanical wave equations. Analogous to how surface tension causes micro-phenomena in fluid mechanics, quantum particles are created when the same tools are applied in Lorentz geometry. It will be shown that gravitation and this form of quantum mechanics can coexist in Einstein’s general relativity by replacing Newton’s constant with a stable anisotropic coupling tensor. The aim of this presentation is to work towards a unified field theory without extra dimensions, parallelism, or manipulation of the metric tensor. |

4:15 - 4:30 | H-T Model, Mehdi Ameri* (Shahid Chamran University of Ahvaz) | The idea tries to explain the direct effects of nonlocal Higgs field variations on time which time here act as an extra quantized field. |

4:30 - 4:45 | Optimized convolutional neural networks for the detection of gravitational wave signals, Scott Field (UMassD) | Gravitational wave astronomy can benefit from the rapid classification of gravitational wave signals buried deep in instrumentation noise. In 2017, George and Huerta (and since then other researchers) have considered Convolutional Neural Networks to detect gravitational wave signals and estimate some of the corresponding binary's parameters. In this talk, I will describe extensions of this classification strategy. In particular, we discuss strategies to optimize the hyperparameters of our network, in an attempt to make our networks as compact and effective as possible. |

4:45 - 5:45 | Hors d'oeuvres (CCB lobby and patio) |

6:00 - 7:00 | Rainer Weiss' public lecture (Main Auditorium, Campus Center) |

Time | |
---|---|

8:30 - 9:15 | Check-in and breakfast (CCB lobby) |

Talk | Abstract | |
---|---|---|

9:15 - 9:30 | Systematics on Gravitational Waves from Neutron Star-Black Hole Mergers using Hybridized Post Newtonian-Numerical Relativity Waveforms, Yiwen Huang* (MIT ) | LIGO and Virgo have started their third observing run in April 2019. There is a chance that a new type of compact binary source of gravitational waves, neutron star-black hole mergers, may be detected. It is important to understand systematic effects in the current parameter estimation (PE) pipeline of LIGO-Virgo, before we are able to interpret PE results if such sources are found. In this talk, we focus on current progress on investigating systematics of gravitational wave PE on neutron star-black hole mergers, using hybridized waveforms with post-newtonian waveforms for inspiral, and numerical relativity waveforms from SXS collaboration for post-inspiral. We use multiple waveform approximants to recover injections of hybridized waveforms with high signal-to-noise-ratios and no background noise, and we report preliminary PE results for a merger with mass ratio q=3. In particular, we report results of tidal deformability, a parameter that affects the gravitational wave signals in the first order. The results are broadly consistent among different approximants, with some discrepancies. |

9:30 - 9:45 | Time-Dependent Computational Domains in SpECTRE, Gabriel Bonilla* (Cornell University) | SpECTRE aims to simulate binary black hole and binary neutron star systems in the near future. We will employ a time-dependent mapping between the fixed computational frame and inertial frame in which the compact objects move. The parameters of the mapping are dynamically adjusted by a control system, which has allowed for the simulation of binary systems in our previous code SpEC. We describe these mappings and control systems, and proposed improvements in SpECTRE. |

9:45 - 10:00 | Limitations of Weyl Scalar Extraction, Dante Iozzo* (Cornell University) | Efficient extraction of Weyl scalars from numerical simulations can be performed by means of the characteristic fields of the Weyl tensor evolution system. Whether these extracted quantities can be reliably extrapolated to asymptotic null infinity is subject to several limitations, including junk radiation backscattering. We discuss these limitations and assess to what extent the asymptotic Weyl scalars can be computed from simulations of binary black hole spacetimes. |

10:00 - 10:15 | A Surrogate Model for Small to Large Mass-Ratio Black Hole Binaries, Nur-E-Mohammad Rifat* (UMassD) | We present a EMRI-based surrogate model that is trained on waveform data generated by for comparable mass-ratio binaries and point-particle black hole perturbation theory for large mass-ratio systems, thus vastly expanding the parameter range of the model. We also note that the gravitational waveforms generated through a simple application of ppBHPT to the comparable mass-ratio cases agree remarkably well with those from NR. |

10:15 - 10:30 | Modeling matter outflows from black hole-neutron star mergers, Francois Foucart (University of New Hampshire) | Understanding the mass, composition and velocity of matter outflows in neutron star mergers is a necessary step if we want to use the post-merger kilonova signal to reliably extract information about the merging compact objects. In this talk, I will review what general relativistic simulations already tell us about matter outflows from black hole-neutron star binaries, the most important sources of uncertainty in the associated kilonova models, and the potential for low-mass black hole-neutron star mergers to be mistaken for neutron star binaries. |

10:30 - 10:45 | Large Eddy Viscosity in Simulations of Differentially Rotating Neutron Stars, Alexander Knight* (University of New Hampshire) | Viscosity in neutron star simulations, particularly in binary mergers, can affect the gravitational wave and neutrino emissions, as well as the post-merger remnant. In this talk, we will present the results of simulating with SpEC a differentially rotating neutron star with large eddy viscosity. We study heating and angular momentum transport for different viscosity models, and compare the advantages and disadvantages of each model. |

10:45 - 11:00 | A spectrally convergent method for wave equations with delta function source terms, Ed McClain* (UMassD) | Hyperbolic equations with source terms containing Dirac delta functions (δ(x)) occur in many areas of physics, including General Relativity (GR). For extreme mass ratio binary (EMRB) systems solving the full Einstein equation currently impossible, and a tractable approach is to linearize the equation around a fixed background spacetime. This perturbation approximation method introduces δ(x) functions, and their derivatives, in the source term which models the smaller compact object. The general method of handling these distributional source terms numerically has often been by approximating the function with a narrow Gaussian, which introduces large errors near the smaller object. In this work we develop a Discontinuous Galerkin method to solve systems driven by δ(x) functions exactly, without any approximation. As proof of concept, several wave equations will be solved in 1+1D using source terms that not only contain δ(x) functions, but also any n^{th}-order derivatives of the delta function. Our method should prove useful for numerically solving the Teukolsky equation, which has source terms proportional to δ(x), δ′(x), and δ″(x). |

11:00 - 11:30 | Coffee Break (CCB lobby) | Coffee Break (CCB lobby) |

Talk | Abstract | |
---|---|---|

11:30 - 11:45 | Phase transitions in black holes of massive gravity, Sharmanthie Fernando (Northern Kentucky University) | In this talk I will present phase transitions of black holes in massive gravity. The black hole considered here belong to a theory of massive gravity where the graviton gain a mass due to Lorentz symmetry breaking. We have computed various thermodynamical quantities such as temperature, pressure, Gibbs free energy an d specific heat capacity. The local and the global thermodynamical stability of the black holes are studied in detail. For a specific value of the parameter in the theory, the black holes undergo a first order phase transition similar to the Van der Waals phase transitions between gas and liquid under constant temperature. This transition is between the small and the large black holes. |

11:45 - 12:00 | Critical gravitational collapse and far-from-equilibrium dynamics in holographic quantum field theories, Paul Chesler (Harvard) | TBD |

12:00 - 12:15 | Three Roads to Quaternion Gravity, Douglas Sweetser (Quaternions.com) | Three roads merge to create a different approach to gravity. Our deepest insights into nature use symmetries because symmetries remain unchanged. Using quaternion algebra instead of tensor calculus, the conservation of space-times-time is the symmetry underlying the quaternion gravity proposal for non-inertial observers in a gravitational field. Where there is a symmetry, there need also be a transformation law to detail how change is permitted to happen. The notion of relaxed relativity holds that in a gravitational field, one observer looking at another observer measuring the speed of light will find the product of wavelength and frequency differs from the speed of light c in a precise way (c'=cγ²esc). Lorentz invariance remains for inertial observers, but non-inertial observers are governed by different symmetries. Gravity is different everywhere, so a field theory is also necessary using gravitational escape velocities. With some reasonable guesses constrained by observations, one can form a quaternion gravity proposal that is consistent with weak field gravity tests to first order Parameterize Post Newtonian accuracy. No gravitons are required for this technical variant of special relativity. Pre-print available on line: http://bit.ly/vp-three-roads |

12:15 - 12:30 | Extension of the Covariance Group of GR: Solar System Model, Edward Lee Green (University of North Georgia) | Pandres has shown that an enlargement of the covariance group to the group of conservative transformations leads to a richer geometry than that of general relativity. Using orthonormal tetrads as field variables, the fundamental geometric object is the curvature vector denoted by C_{μ}. From an appropriate scalar Lagrangian field equations for both free-field and the field with sources have been developed. We first review models which use a free-field solution to model the Solar System and why these results are unacceptable. We also show that the standard Schwarzschild metric is also unacceptable in our theory. Finally we show that there are solutions which involve sources which agree with general relativity PPN parameters and thus approximate the Schwarzschild solution. The main difference is that the Einstein tensor is not identically zero but includes small values for the density, radial pressure and tangential pressure. |

12:30 - 12:45 | Hyper Space, Michael Sajib | TBD |

12:45 - 1:00 | Award for best student talk (Sponsored by DGRAV), closing remarks | Award for best student talk (Sponsored by DGRAV), closing remarks |