Inaugural Conference Poster

At LHC energies it is possible to generate BSQ (baryon, strangeness, and electric) charge fluctuations from gluon splittings into quark anti-quark pairs, generated within the ICCING model. Here we propagate these conserved charges within an upgraded version of the hydrodynamic model, v-USPhydro, that conserves BSQ coupled to a 4-D equation of state {T,μB,μS,μQ} from Lattice Quantum Chromodynamics. We find that solely due to charge fluctuations that we expect large fluctuations in the chemical potentials {μB,μS,μQ} in local fluid cells at freeze-out even at LHC energies.

While it is well known that there is a significant amount of conserved charges in the initial state of nuclear collisions, the production of these due to gluon splitting has yet to be thoroughly investigated. The ICCING (Initial Conserved Charges in Nuclear Geometry) algorithm reconstructs these quark distributions, providing conserved strange, baryon, and electric charges, by sampling a given model for the gluon to quark pair splitting function over the initial energy density, which is valid at top collider energies, even when baryon chemical potential is zero. The ICCING algorithm includes fluctuations in the gluon longitudinal momenta, a structure that supports the implementation of dynamical processes, and the c++ version is now open-source. A full analysis of parameter choices on the model has been done to quantify the effect these have on the underlying physics. We find there is a sustained difference across the different charges that indicates sensitivity to hot spot geometry.

Gravitational waves emitted by inner binaries in hierarchical triple systems are interesting astrophysical candidates for space-based detectors such as the Laser Interferometer Space Antenna, LISA. In the presence of a third body, such as a supermassive black hole, an inner binary consisting of intermediate mass black holes can undergo oscillations in eccentricity and inclination angle because of the Kozai-Lidov mechanism. We construct ready-to-use gravitational waveforms in the Fourier domain, taking into account the Kozai-Lidov effect within the framework of post-Newtonian (PN) theory. The separation of timescales in the system allows us to use multiple-scale analysis to combine the effects of both Kozai-Lidov oscillations and PN effects. To leading order in conservative and dissipative dynamics, we constructed a preliminary model by assuming small eccentricity and obtained analytic solutions describing the evolution of the orbital elements. We used the stationary phase approximation and computed the resulting imprint on the gravitational waveform in the Fourier domain. We found that the oscillations have a clear signature on the Fourier amplitude of the waveform while leaving a measurable imprint on the gravitational wave phase. We also found that our analytic results are consistent with numerics. Further, we identified potential source candidates in the LISA band for which the KL effect could be significant. As part of our ongoing work, we extend our preliminary model to larger eccentricities and to next-to-leading order in PN theory. We use this extended model for parameter estimation, which can provide direct evidence of the astrophysical formation channel. We also use our model for studies on waveform systematics and for tests of general relativity.

We present Lyapunov exponents for null geodesics around extremal black holes in two quadratic gravity theories, dynamical-Chern-Simons (dCS) and scalar-Gauss-Bonet (sGB). Further, we comment on how these Lyapunov numbers can be used to constrain these theories.

The search for the Quantum Chromodynamics (QCD) critical point is underway at the Relativistic Heavy-Ion Collider (RHIC) Beam Energy Scan II. The primary signature of the critical point is a peak (divergence) in the kurtosis of the net-proton number distribution, $\kappa_4$. Most previous studies of kurtosis have focused on equilibrium physics, whereas it is well-known that out-of-equilibrium effects are vital in understanding the Quark Gluon Plasma (QGP). Out-of-equilibrium effects near the vicinity of the critical point can dramatically alter the trajectory through the QCD phase diagram from equilibrium. We find that the size and shape of the critical region play an important role in whether or not the critical point will be effectively seen in the dynamic evolution. Critical regions which extend in the $T$ direction have a stronger dip in the speed of sound, which focus trajectories towards the critical point and influence the kurtosis.

Ultra-light massive scalar fields arise from string theory as axion-like particles and represent compelling wave-like dark matter candidates. When in the proximity of a rotating black hole, such fields can form macroscopic condensates through accretion or superradiant instability. In the late stages of a black hole binary coalescence, the presence of these scalar clouds may lead to specific imprints in the gravitational wave emission, additional scalar (dipole) radiation and further dynamical features. We will present novel numerical relativity simulations for which we self-consistently solve the Einstein-Klein-Gordon equations by constructing constraint satisfying initial data. We then discuss implications of our results for gravitational-wave observations. (work in collaboration with Cheng-Hsin Cheng and Helvi Witek)

Recent and ongoing advances in gravitational-wave astronomy have the potential to revolutionize our understanding of the universe. Observations have shown that ultradense matter must be stiffer than previously thought, with a speed of sound potentially peaking above 1/2 the speed of light [1]. We explore the potential consequences of the large speed-of-sound peak in the equation of state of cold and dense nuclear matter and propose a new mechanism to explain this feature and implement it nuclear physics models [2]. In a different context, gravitational waves might reveal previously invisible dark compact objects, made entirely of self-gravitating dark matter. We discuss how gravitational waves might lead to the discovery of mirror dark matter, by revealing neutron stars composed of dark baryons, called mirror neutron stars. To estimate the tell-tale signatures of these objects, results from lattice-QCD and nuclear physics are combined with constraints from particle physics and calculations in general relativity, in a multi-disciplinary effort [3]. [1] Christian Drischler, Sophia Han, James M. Lattimer, Sanjay Reddy, Tianqi Zhao, Phys. Rev. C 103, 045808 (2021). [2] Maurício Hippert, Eduardo S. Fraga, Jorge Noronha, Phys. Rev. D 104, 034011 (2021). [3] Maurício Hippert, Jack Setford, Hung Tan, David Curtin, Jacquelyn Noronha-Hostler and Nicolás Yunes, arXiv:2103.01965.

To extract the viable neutron star equation of state (EoS) band from neutron star mergers, one requires functional forms of the EoS. One of three methods are used-- spectral functions, piecewise polytropes, or gaussian process estimations. However, realistic nuclear physics models containing deconfined QCD matter may present nontrivial features associated with phase transitions, such as dramatic bumps and dips in the speed of sound, that cannot be captured by these smooth functions. This behavior in the speed of sound is particularly relevant to the production of ultra-heavy neutron stars that support stellar masses compatible with GW190814. We reconcile the versatility of the model agnostic gaussian process approach with nuclear physics by introducing non-trivial features in the EoS. By coupling the new EoS with an active learning framework, we can quickly rule out Equations of State that do not fit within constraints from NICER and gravitational waves.

The inclusion of fluctuations is necessary for modeling the quark-gluon plasma near the quantum chromodynamics critical point. Given the success of relativistic hydrodynamics for modeling the behavior of heavy-ion collisions and neutron star mergers, including fluctuations in these models is essential for describing physics near this critical point. Including such fluctuations is done using the fluctuation-dissipation theorem, which relates the retarded Green's function of a dissipative system to the correlation functions of fluctuations. Models for which fluctuating hydrodynamics has been formulated thus far [1] have employed standard relativistic Navier-Stokes theory, which is known to be acausal and unstable. We show that such models do not necessarily have a retarded Green's function in a general Lorentz frame, meaning the fluctuation-dissipation theorem cannot be used to determine stochastic correlations. Relativistic Navier-Stokes can be generalized to a class of first-order models that are causal, stable, and well-posed, known as BDNK theory [2,3]. The retarded Green's function is derived for these models, in the conformal case, as a starting point for including fluctuations in causal relativistic hydrodynamics. [1] X. An, G. Basar, M. Stephanov and H. U. Yee, Phys. Rev. C 100 no. 2, 024910 (2019); Phys. Rev. C 102. [2] F. S. Bemfica, M. M. Disconzi and J. Noronha, Phys. Rev. D 98 (2018), 104064; Phys. Rev. D 100 (2019) 10, 204020; arXivL2009.11388. [3] P. Kovtun, JHEP 10 (2019) 034.

The properties of clusters and dark matter halos are incredibly important to improve our understanding of cosmology. At the present epoch, clusters are not yet virialized due to continuing accretion and mergers. But, due to the accelerating expansion of the universe, in the future structure formation will effectively freeze out and become virialized. Here I present the results of cosmological N-body simulations that I ran past the present epoch, up to a = 100. I show that a spherical collapse model accurately describes the boundary of the halos in the final snapshot with a distinct boundary between particles falling into the halo and particles following the Hubble flow away from the halo. I additionally compare these results with the traditional friends-of-friends method of finding halos in simulations. This work will provide the foundation for future work to understand the structure and evolution of dark matter halos.

Gravitational waves emitted during compact binary coalescence offer a unique way to observe strong gravity systems directly. Models of the signals produced by coalescence events, derived from general relativity or modified theories of gravity, are used to extract information from gravitational wave data. However, due to the complexity of the theories and computational time constraints, these models are necessarily approximations. Systematic error - or error in parameter estimation resulting from a mismatch between the approximate model and nature - has been studied in depth over the last decades in the context of gravitational waves. We propose to add to this body of knowledge with an injection and recovery campaign to study, in particular, the impact post Newtonian corrections to the gravitational wave phase have on systematic error in parameters recovered from signals produced by inspiraling black hole binaries. We will consider injected data of non-spinning binaries as detected by ground-based observatories and recover with models of varying PN order in the phase. We will explore the conditions under which the dominant source of error in parameter estimation is systematic rather than statistical.

The production of relativistic jets by accreting black holes requires the presence of strong poloidal magnetic fields near the event horizon. However, most known physical processes are thought to strengthen magnetic fields in the toroidal directions. Recently, numerical GRMHD simulations were used to show that accretion disks with a purely toroidal magnetic field can create poloidal magnetic fields strong enough to launch jets via a large-scale dynamo (Liska et al. 2020). Prior to this analysis, it seemed likely that this dynamo functioned similarly to the alpha-omega dynamo, which generates poloidal fields in the Sun. This poster summarizes work that I conducted to determine the dynamo's mechanism. The dynamo creates four loops of alternating polarity. To determine if the alpha-process could account for these changes in polarity, I analyzed how the expansion, compression, and velocity of the fluid vary throughout the disk, and how they relate to each other. I found that changes in the expansion / compression and direction of motion of the fluid across different regions of the disk correspond to changes in loop polarity. However, these changes appear inconsistent with the alpha-process. Nonetheless, they provide strong clues to the dynamo’s actual mechanism.

In the era of gravitational wave astronomy, there are a diverse number of ways to test general relativity. One common method is the parametrized inspiral test. Starting with a gravitational wave model calculated from a post-Newtonian expansion in general relativity (an expansion in the orbital velocity and the gravitational potential), one can modify the waveform model by appending a deformation parameter to one of the coefficients in the series. General relativity would predict that this deformation parameter should be zero. However, if this waveform model is compared against data and the extra parameter is preferred, that would be evidence for physics beyond general relativity. Traditionally, this has been done one coefficient at a time, but there is concern that this framework might be overly restrictive, as including modifications to multiple coefficients at once typically degrades constraints. To determine if current constraints (using a single parameter at a time) are robust, we introduce a new deformation parametrization and prior, inspired by the post-Newtonian calculation. Using this new waveform model with up to five additional deformations, we see constraints actually improve. From this result, we conclude that current constraints derived with the simpler, single-deformation waveform model are robust.

Our ability to test gravity with gravitational wave detectors is limited by our ability to accurately construct a gravitational waveform template. Thus, it is important to construct such templates for modified theories of gravity. Einstein-æther theory is a particularly interesting modified theory of gravity because it is the most generic Lorentz-violating theory one can construct with one additional vector field and its first derivatives. As well as modifying the amplitude and phase of the gravitational wave, this theory contains scalar and vector polarizations in addition to the tensor polarizations of general relativity. Therefore, any waveform model that can describe gravitational waves in this theory must include extra polarizations in the detector response function, which can travel with speeds different than that of light. With this poster I will describe the construction of such a waveform through modification of the general relativity IMRPhenomD_NRTidalv2 model (used by the LIGO/VIRGO Collaboration) and explain how recent calculations of the sensitivity for neutron stars in the theory make this possible. I will outline the current constraints on the theory and describe what constraints can be placed by gravitational wave data.

Physics Outreach at Illinois through New Technologies (POINT) is an ICASU project aimed at generating interest in physics for middle school and high school students through virtual reality (VR). Our goal is to increase student engagement with science and encourage more students to pursue AP and college physics courses. This project includes two major goals: incorporating VR headsets and existing science demonstrations into outreach programs and developing further simulations to explain the fundamental physics of gravity and general relativity.

My research establishes connections between fluid dynamics, quantum field theory and mathematical physics to develop new tools to characterize novel properties of strongly-interacting systems. A considerable part of my work aims at a better understanding of the laws of relativistic spin hydrodynamics, i.e., the theory of relativistic hydrodynamics when quantum spin degrees of freedom play an important role and influence the behavior of the fluid. I study applications mainly to the physics of the quark-gluon plasma, but I am also interested in exploring connections to other fields such as neutron star mergers and condensed matter. Relativistic spin hydrodynamics offers a unique way to gain a deeper knowledge of strongly-interacting matter and to study those quantum effects which are amplified to the macroscopic level.

The binary love relation is an Equation of State insensitive relation that can be used to break the degeneracy of neutron star observables. However, with advance of gravitational wave (GW) detectors, information of neutron star cores can be extracted from GW observations. In this talk, I will discuss how the observation of the binary love relation may reveal some specific features in the equation of state, which imply new degree of freedom at the core.

The detection of gravitational waves from compact binary mergers by the LIGO/Virgo collaboration has, for the first time, allowed us to test relativistic gravity in its strong, dynamical and nonlinear regime, thus opening a new arena to confront general relativity (and modifications thereof) against observations. We consider a theory that modifies general relativity by introducing additional degrees of freedom, such as dynamical Chern Simons gravity for instance. In such theories, spinning black holes are different from their general relativistic counterparts, and can thus serve as probes of these theories. We modify the Teukolsky formalism to obtain a set of linear coupled differential equations that describe dynamical gravitational perturbations of a rotating black hole in theories beyond GR to all orders in spin. Through this poster, I will present the modified Teukolsky formalism and the equations describing the evolution of dynamical gravitational perturbations. Additionally, I will describe the calculation of the black hole’s quasi-normal mode frequencies to leading order in spin, and compare these to previously obtained results. This formalism lays down the foundations for the general extension of the calculation of quasi-normal mode frequencies for black holes that rotate arbitrarily fast in beyond GR theories, therefore extending results valid in Petrov Type D backgrounds to Petrov type I backgrounds.

The metric of a spacetime can be greatly simplified if the spacetime is circular. In this poster I will show that in generic effective theories of gravity, the spacetime of a stationary, axisymmetric, and asymptotically flat solution must be circular if the solution can be obtained as a perturbation of the general relativistic solution. This result applies to a broad class of gravitational theories that include arbitrary scalars and vectors in their light sector, so long as their nonstandard kinetic terms and nonmininal couplings to gravity are treated perturbatively.

Neutron stars equations of state that can sustain heavy neutron stars over 2 Msun necessitate a large, rapid rise in the speed of sound above the causal limit. These equations of state are electrically neutral and assume vanishing temperatures. In order to compare to laboratory experiments (i.e. heavy-ion collisions) we must convert our equations of state over to nearly symmetric nuclear matter where the number of protons and neutrons are approximately equal. Here we apply the symmetry energy expansion with 4 coefficients and test the bounds of these coefficients that support causal equations of state both for neutron stars and heavy-ion collisions. Next we explore the effect of strangeness on the symmetry energy expansion because strangeness plays a significant role in heavy-ion collisions.