Nontrivial features in the speed of sound inside neutron stars

Measurements of neutron star masses, radii, and tidal deformability have direct connections to nuclear physics via the equation of state (EoS), which for the cold, catalyzed matter in neutron star cores is commonly represented as the pressure as a function of energy density. Microscopic models with exotic degrees of freedom display nontrivial structure in the speed of sound ($c_s$) in the form of first-order phase transitions and bumps, oscillations, and plateaus in the case of crossovers and higher-order phase transitions. We present a procedure based on Gaussian processes to generate an ensemble of EoSs that include nontrivial features. Using a Bayesian analysis incorporating measurements from X-ray sources, gravitational wave observations, and perturbative QCD results, we show that these features are compatible with current constraints. We investigate the possibility of a global maximum in $c_s$ that occurs within the densities realized in neutron stars -- implying a softening of the EoS and possibly an exotic phase in the core of massive stars -- and find that such a global maximum is consistent with, but not required by, current constraints.Comment: 31 pages, 9 figure

Searching for phase transitions in neutron stars with modified Gaussian processes

Gaussian processes provide a promising framework by which to extrapolate the equation of state (EoS) of cold, catalyzed matter beyond $1-2$ times nuclear saturation density. Here we discuss how to extend Gaussian processes to include nontrivial features in the speed of sound, such as bumps, kinks, and plateaus, which are predicted by nuclear models with exotic degrees of freedom. Using a fully Bayesian analysis incorporating measurements from X-ray sources, gravitational wave observations, and perturbative QCD results, we show that these features are compatible with current constraints and report on how the features affect the EoS posteriors.Comment: 10 pages, 4 figures, CSQCD IX proceeding

Lattice-QCD-based equations of state at finite temperature and density

The equation of state (EoS) of QCD is a crucial input for the modeling of heavy-ion-collision (HIC) and neutron-star-merger systems. Calculations of the fundamental theory of QCD, which could yield the true EoS, are hindered by the infamous Fermi sign problem which only allows direct simulations at zero or imaginary baryonic chemical potential. As a direct consequence, the current coverage of the QCD phase diagram by lattice simulations is limited. In these proceedings, two different equations of state based on first-principle lattice QCD (LQCD) calculations are discussed. The first is solely informed by the fundamental theory by utilizing all available diagonal and non-diagonal susceptibilities up to $\mathcal{O}(\mu_B^4)$ in order to reconstruct a full EoS at finite baryon number, electric charge and strangeness chemical potentials. For the second, we go beyond information from the lattice in order to explore the conjectured phase structure, not yet determined by LQCD methods, to assist the experimental HIC community in their search for the critical point. We incorporate critical behavior into this EoS by relying on the principle of universality classes, of which QCD belongs to the 3D Ising Model. This allows one to study the effects of a singularity on the thermodynamical quantities that make up the equation of state used for hydrodynamical simulations of HICs. Additionally, we ensure that these EoSs are valid for applications to HICs by enforcing conditions of strangeness neutrality and fixed charge-to-baryon-number ratio.Comment: Contribution to the 37th Winter Workshop on Nuclear Dynamics. arXiv admin note: text overlap with arXiv:2103.0814

Data Compression and Machine Learning in the Analysis of the Entropy of Photodissociation in Organic Donor-Acceptor Interfaces

Organic photovoltaics have become increasingly relevant in recent years, resulting in a growing demand for theoretical models that can accurately approximate the behavior of electrons in organic donor-acceptor inter- faces. As an attempt to simplify the analysis of electron-hole dynamics, we make a case for the use of the Shannon Entropy as measure of the degree of entanglement of e-h pairs using Schmidt decomposition. The Schmidt form also allows us to determine the number of effective dimen- sions occupied by an arbitrary eigenstate Ψk in Hilbert space. In the case of a 50 × 50 diabatic density matrix for a 1-D system, we were able to reduce the number of bytes required to store this information by ∼65% using the Schmidt form. We then reconstructed the original matrix from the reduced model and calculated values for charge transfer character and inverse participation ratio and found that the average percent error was less than 0.05% in both cases. Lastly, we demonstrate that machine learn- ing algorithms can be used to accurately differentiate between excitonic, charge-transfer, and charge-separated states. By combining data compres- sion and machine learning, we developed a simplified and computationally efficient way to quickly sift through thousands of eigenstates and single out relevant information regarding the Shannon Entropy and charge sep- aration. We present the results of this analysis for a 1-D interface with 50 sites and energetic offsets varying between 0.0 - 0.5 eV.Honors CollegeChemistry, Department o

Initial Stages 2021

One of the main goals of the second phase of the Beam Energy Scan program at RHIC is to search for the QCD critical point. In order to study the thermodynamic effects of the presence of a critical point, we constructed a family of equations of state using a model that couples Lattice QCD results to a parameterized critical point from the 3D Ising model universality class. The mapping of the Ising critical point onto the QCD phase diagram gives rise to free parameters that control its position and size/shape of the critical region. In this work, we demonstrate how active sampling coupled with a variety of machine learning models can be used as a tool to identify choices of free parameters that result in inconsistent thermodynamics. In particular, we study the performance of supervised logistic regression, Support Vector Machine (SVM), random forest, and deep learning algorithms, in both passive and active learning settings. This approach can rule out pathological parameter sets at a low computational cost. Our procedure can be applied to constrain other high-dimensional models relevant to experimental searches in heavy-ion collisions

Off-of-equilibrium effects on Kurtosis Along Strangeness-Neutral Trajectories

The Beam Energy Scan program at the Relativistic Heavy Ion Collider (RHIC) is searching for the QCD critical point. The main signal for the critical point is the kurtosis of the distribution of proton yields obtained on an event by event basis where one expects a peak at the critical point. However, its exact behavior is still an open question due to out-of-equilibrium effects and uncertainty in the equation of state. Here we use a simplistic hydrodynamic model that enforces strangeness-neutrality, selecting trajectories that pass close to the critical point. We vary the initial conditions to estimate the effect of out-of-equilibrium hydrodynamics on the kurtosis signal

QCD equation of state matched to lattice data and exhibiting a critical point singularity

We construct a family of equations of state for QCD in the temperature range 30MeV≤T≤800MeV and in the chemical potential range 0≤μ_{B}≤450MeV. These equations of state match available lattice QCD results up to O(μ_{B}^{4}) and in each of them we place a critical point in the three-dimensional (3D) Ising model universality class. The position of this critical point can be chosen in the range of chemical potentials covered by the second Beam Energy Scan at the Relativistic Heavy Ion Collider. We discuss possible choices for the free parameters, which arise from mapping the Ising model onto QCD. Our results for the pressure, entropy density, baryon density, energy density, and speed of sound can be used as inputs in the hydrodynamical simulations of the fireball created in heavy ion collisions. We also show our result for the second cumulant of the baryon number in thermal equilibrium, displaying its divergence at the critical point. In the future, comparisons between RHIC data and the output of the hydrodynamic simulations, including calculations of fluctuation observables, built upon the model equations of state that we have constructed may be used to locate the critical point in the QCD phase diagram, if there is one to be found

SORA Payload: Stratospheric Organisms and Radiation Analyzer

SORA’s scientific objectives are to design and build a novel system that will isolate surrounding air and sample for cells, utilize the onboard sensors to analyze exposure to solar and cosmic radiation that microorganisms may encounter, monitor the environmental conditions such as temperature, pressure, and humidity. Payload will sample for: Existence of microorganisms. Bacterial spores in the upper atmosphere. Environmental data such as radiation exposure, temperature, pressure and humidity. All integration, thermal and vacuum testing has now been concluded and the payload is deemed flight ready. Final flight preparations are being made for the mission during the first week of September.Physics, Department ofHonors Colleg

Demographic study of major conferences in heavy ion physics

International audienceWe present a study of the demographics of major conferences in heavy ion physics. We look at the distribution of talks by gender for Quark Matter, Strangeness in Quark Matter, Initial Stages, and Hard Probes between 2011–2022. We find that women are often underrepresented among plenary speakers and usually underrepresented among parallel speakers. At Quark Matter, women are more likely to be given a poster presentation in lieu of an oral presentation. The Quark Matter summary talk has never been given by a woman. We discuss the collection of data and possible approaches to make the field more equitable and, therefore, more scientifically productive