Modeling the large-scale redshift-space 3-point correlation function of galaxies

We present a configuration-space model of the large-scale galaxy 3-point correlation function (3PCF) based on leading-order perturbation theory and including redshift space distortions (RSD). This model should be useful in extracting distance-scale information from the 3PCF via the Baryon Acoustic Oscillation (BAO) method. We include the first redshift-space treatment of biasing by the baryon-dark matter relative velocity. Overall, on large scales the effect of RSD is primarily a renormalization of the 3PCF that is roughly independent of both physical scale and triangle opening angle; for our adopted $\Omega_{\rm m}$ and bias values, the rescaling is a factor of $\sim 1.8$. We also present an efficient scheme for computing 3PCF predictions from our model, important for allowing fast exploration of the space of cosmological parameters in future analyses.Comment: 23 pages, 11 figures, submitted MNRA

A Practical Computational Method for the Anisotropic Redshift-Space 3-Point Correlation Function

We present an algorithm enabling computation of the anisotropic redshift-space galaxy 3-point correlation function (3PCF) scaling as $N^2$, with $N$ the number of galaxies. Our previous work showed how to compute the isotropic 3PCF with this scaling by expanding the radially-binned density field around each galaxy in the survey into spherical harmonics and combining these coefficients to form multipole moments. The $N^2$ scaling occurred because this approach never explicitly required the relative angle between a galaxy pair about the primary galaxy. Here we generalize this work, demonstrating that in the presence of azimuthally-symmetric anisotropy produced by redshift-space distortions (RSD) the 3PCF can be described by two triangle side lengths, two independent total angular momenta, and a spin. This basis for the anisotropic 3PCF allows its computation with negligible additional work over the isotropic 3PCF. We also present the covariance matrix of the anisotropic 3PCF measured in this basis. Our algorithm tracks the full 5-D redshift-space 3PCF, uses an accurate line of sight to each triplet, is exact in angle, and easily handles edge correction. It will enable use of the anisotropic large-scale 3PCF as a probe of RSD in current and upcoming large-scale redshift surveys.Comment: 17 pages, 2 figures, MNRAS submitte

Foodi - Automated Ordering System

We worked for BeSprout Technology to create an automated ordering system called Foodi. The Foodi system uses a combination of Java, IBM Watson, and MySQL to gather all the necessary information needed for the conversation, and is dynamic so it can be used in multiple restaurants. Many people still place orders via a phone call, so in an effort to streamline the ordering process, this project was created to enable automatic order placing so employees can focus on other tasks within the restaurant. When a customer calls a restaurant, Foodi will take care of any orders and answer questions the customer may have. The input from the user is sent to Watson, and is filtered through a conversation tree created with IBM’s Bluemix. Bluemix uses the user input to navigate to certain nodes. When a node in the conversation tree is hit, the user input is passed into Java code and parsed appropriately. After the input has been parsed in Java, Watson is told which node in the conversation tree to travel to next and how to respond to the user. This process is repeated until the user is finished ordering and the final order is repeated back to the customer. The restaurant receives the final order and begins preparing the food.https://scholarscompass.vcu.edu/capstone/1181/thumbnail.jp

Resolution Effects in the Hybrid Strong/Weak Coupling Model

Within the context of a hybrid strong/weak coupling model of jet quenching, we study the consequences of the fact that the plasma produced in a heavy ion collision cannot resolve the substructure of a collimated parton shower propagating through it with arbitrarily fine spatial resolution. We introduce a screening length parameter, $L_{\rm res}$, proportional to the inverse of the local temperature in the plasma, estimating a range for the value of the proportionality constant via comparing weakly coupled QCD calculations and holographic calculations appropriate in strongly coupled plasma. We then modify the hybrid model so that when a parton in a jet shower splits, its two offspring are initially treated as unresolved, and are only treated as two separate partons losing energy independently after they are separated by a distance $L_{\rm res}$. This modification delays the quenching of partons with intermediate energy, resulting in the survival of more hadrons in the final state with $p_T$ in the several GeV range. We analyze the consequences of different choices for the value of the resolution length, $L_{\rm res}$, and demonstrate that introducing a nonzero $L_{\rm res}$ results in modifications to the jet shapes and jet fragmentations functions, as it makes it more probable for particles carrying a small fraction of the jet energy at larger angles from the jet axis to survive their passage through the quark-gluon plasma. These effects are, however, small in magnitude, something that we confirm via checking for effects on missing-$p_T$ observables.Comment: 32 pages, 7 figure

Optimal Explicit Strong Stability Preserving Runge--Kutta Methods with High Linear Order and optimal Nonlinear Order

High order spatial discretizations with monotonicity properties are often desirable for the solution of hyperbolic PDEs. These methods can advantageously be coupled with high order strong stability preserving time discretizations. The search for high order strong stability time-stepping methods with large allowable strong stability coefficient has been an active area of research over the last two decades. This research has shown that explicit SSP Runge--Kutta methods exist only up to fourth order. However, if we restrict ourselves to solving only linear autonomous problems, the order conditions simplify and this order barrier is lifted: explicit SSP Runge--Kutta methods of any linear order exist. These methods reduce to second order when applied to nonlinear problems. In the current work we aim to find explicit SSP Runge--Kutta methods with large allowable time-step, that feature high linear order and simultaneously have the optimal fourth order nonlinear order. These methods have strong stability coefficients that approach those of the linear methods as the number of stages and the linear order is increased. This work shows that when a high linear order method is desired, it may be still be worthwhile to use methods with higher nonlinear order