Organizing Committee
 Isabel CorderoCarrión
University of Valencia  Francois Foucart
University of New Hampshire  Steven Liebling
Long Island University  Carlos Palenzuela
Universitat de les Illes Balears  Lorenzo Pareschi
Heriot Watt University  David Radice
Pennsylvania State University
Abstract
The spectacular observation of gravitational waves from a binary neutron star merger by the LIGOVirgo Collaboration (GW170817), and a successful followup campaign by nearly every electromagnetic telescope ushered in this new era of multimessenger astrophysics. Much of the understanding of such events arises from numerical modeling. An important part of this modeling is the inclusion in simulations of neutrino transport, as described by Boltzmann's equation. Because of inherent computational resource limits and given the high cost of the transport equations and the complexity of neutrinomatter interactions, there is a tradeoff between computational cost and physical realism in all simulations. This workshop covers various approaches to solving the neutrino transport problem in compact object mergers and corecollapse supernovae, including Monte Carlo methods, moment truncation schemes, and other techniques.
Confirmed Speakers & Participants
Talks will be presented virtually or inperson as indicated in the schedule below.
 Speaker
 Poster Presenter
 Attendee
 Virtual Attendee

Alexander Alekseenko
California State University Northridge

Maitraya Bhattacharyya
The Pennsylvania State University

Luca Boccioli
University of California, Berkeley

Marie Cassing
Goethe University Frankfurt

Michail Chabanov
Rochester Institute of Technology

Patrick ChiKit Cheong
UC Berkeley

Isabel CorderoCarrión
University of Valencia

Marie Cornelius
University of Copenhagen

Sanjana Curtis
UC Berkeley

Constantine Dafermos
Brown University

Shane Davis
University of Virginia

Giacomo Dimarco
University of Ferrara

Francois Foucart
University of New Hampshire

Irene Gamba
University of Texas at Austin

Tyson George
Virginia Tech

Somdutta Ghosh
NC State University

Danat Issa
Northwestern University

Manuel Izquierdo
University of the Balearic Islands

Jay Kalinani
Center for Computational Relativity and Gravitation, Rochester Institute of Technology

Kyohei Kawaguchi
Max Planck Institute for Gravitational Physics (AEI, PotsdamGolm)

Steven Liebling
Long Island University

Anthony Mezzacappa
University of Tennessee, Knoxville

Jonah Miller
Los Alamos National Laboratory

Elias Most
California Institute of Technology

Nishad Muhammed
Washington State University

Elena Murchikova
Northwestern University

Carlo Musolino
Goethe University Frankfurt

Harry HoYin Ng
Institute for Theoretical Physics, GoetheUniversität Frankfurt

Evan O'Connor
Stockholm University

Martin Obergaulinger
University of Valencia

Arthur Offermans
KU Leuven

Carlos Palenzuela
Universitat de les Illes Balears

Lorenzo Pareschi
Heriot Watt University

David Radice
Pennsylvania State University

Colter Richardson
University Of Tennessee, Knoxville

Sherwood Richers
University of Tennessee, Knoxville

Milton Ruiz
University of Valencia

Federico Schianchi
University of Potsdam

Anna Suliga
University of California, Berkeley

Irene Tamborra
University of Copenhagen

Konrad Topolski
Goethe University Frankfurt

Allen Wen
Rochester Institute of Technology

Yulong Xing
The Ohio State University

Yukun Yue
University of Wisconsin, Madison
Workshop Schedule
Monday, July 8, 2024

8:30  8:50 am EDTCheck In11th Floor Collaborative Space

8:50  9:00 am EDTWelcome11th Floor Lecture Hall
 Session Chair
 Brendan Hassett, ICERM/Brown University

9:00  9:45 am EDTRadiation Transfer Methods for Relativistic Spacetimes11th Floor Lecture Hall
 Speaker
 Shane Davis, University of Virginia
 Session Chair
 Jay Kalinani, Center for Computational Relativity and Gravitation, Rochester Institute of Technology
Abstract
I will review efforts to model radiation transfer in relativistic spacetimes, describing different methods and approaches. I will discuss the pros and cons of these methods in their application to accreting black hole systems and report on recent results solving the transfer equation directly. I will endeavor to highlight some points of contact between photon radiation transfer applications in accreting systems and neutrino transport in core collapse and compact object mergers.

10:00  10:30 am EDTCoffee Break11th Floor Collaborative Space

10:30  11:15 am EDTMonte Carlo transport for postmerger and collapsar disks11th Floor Lecture Hall
 Speaker
 Jonah Miller, Los Alamos National Laboratory
 Session Chair
 Jay Kalinani, Center for Computational Relativity and Gravitation, Rochester Institute of Technology
Abstract
The 2017 detection of the inspiral and merger of two neutron stars was a landmark discovery in astrophysics. Through a wealth of multimessenger data, we now know that the merger of these ultracompact stellar remnants is a central engine of short gamma ray bursts and a site of rprocess nucleosynthesis, where the heaviest elements in our universe are formed. The radioactive decay of unstable heavy elements produced in such mergers powers an optical and infrared transient: The kilonova. One key driver of nucleosynthesis and resultant electromagnetic afterglow is wind driven by an accretion disk formed around the compact remnant. Neutrino transport plays a key role in setting the electron fraction in this outflow, thus controlling nucleosynthesis. Collapsars are black hole accretion disks formed after the core of a massive, rapidly rotating star collapses to a black hole. These dramatic systems rely on much the same physics and modeling as postmerger disks, and can also be a key driver of rprocesses nucleosynthesis. I present recent progress in modeling these enigmatic systems, with an emphasis on both the impact and techniques of detailed Monte Carlo neutrino transport.

11:30 am  12:15 pm EDTFrom ChapmanKolmogorov and Master equations from probability methods to the kinetic dynamics of neutrinosantineutrinos modeled by Boltzmann FermiDirac systems11th Floor Lecture Hall
 Speaker
 Irene Gamba, University of Texas at Austin
 Session Chair
 Jay Kalinani, Center for Computational Relativity and Gravitation, Rochester Institute of Technology
Abstract
The linking of physics particle system in mean fields or interacting as multispecies systems can be viewed as a probabilistic model as envisioned by L. Boltzmann and G. Maxwell of dissipative stochastic dynamics of one or more species marking the birth of thermodynamics by expectations of statistical flows. In the early Twentieth Century, the introduction of electron and ions systems and the raise of particle charge and neutral particle dynamics the Boltzmann ideas were extended by Dirac and Fermi to encompassed an accurate model to describe electromagnetic forces and braking of symmetry, and so the BoltzmannDiracFermi model arose as an accurate statistical frame work of understanding the hotelectron dynamics in solid states modeled by BoltzmannDiracFermi in terms of the statistical frameworks of thermodynamics for nanoelectronics. At the same time the raise of astrophysical systems, in the absence of easily observable experimental data become W. Pauli proposed neutral particles that can dissipate relativistic electron dynamics, and labeled them neutrinos and antineutrinos as a possible dissipative mechanisms. I will present a natural link between the probabilistic framework from ChapmanKolmogorov flows the evolution of Nparticle systems from different species that under ergodic assumptions that are sufficient for near space homogeneous system at the particle level for model reduction emerge a kinetic systems for neutrino and antineutrino particles couples to equations of relativized matter equations for rest mass density, with temperature and electron fraction rates depending on spacetime, all in a spherical coordinate framework. We’ll discuss conservation properties for the system, entropies, and the natural GalerkinPetrov kinetic scheme as a very efficient tool for fast solvers for this reduced model.

12:30  2:30 pm EDTLunch/Free Time

2:30  3:00 pm EDTTBA11th Floor Lecture Hall
 Speaker
 Sanjana Curtis, UC Berkeley
 Session Chair
 Shane Davis, University of Virginia

3:10  4:00 pm EDTCoffee Break11th Floor Collaborative Space

4:00  4:15 pm EDTAsterX: a new opensource GPUaccelerated GRMHD code for dynamical spacetimesShort Talk  11th Floor Lecture Hall
 Speaker
 Jay Kalinani, Center for Computational Relativity and Gravitation, Rochester Institute of Technology
 Session Chair
 Shane Davis, University of Virginia
Abstract
With an increasing demand of extensive parallel computing in numerical simulations addressing various astrophysical problems, codes which can efficiently work on GPUs are the need of the hour. In this talk, I will discuss the salient features of a new opensource general relativistic magnetohydrodynamic (GRMHD) code AsterX, which is built upon CarpetX, a new driver for the Einstein Toolkit. AsterX is based on the fluxconservative Valencia formulation, considering staggered vector potential evolution. It designed to work on GPUs and also takes advantage of the blockstructured adaptive mesh refinement provided by CarpetX through the AMReX framework. I will also discuss the various stringent 1D, 2D and 3D GRMHD tests performed with AsterX on the Frontier cluster, and also present scaling results.

4:20  4:50 pm EDTSimulating collapsars with neutrino transport11th Floor Lecture Hall
 Speaker
 Danat Issa, Northwestern University
 Session Chair
 Shane Davis, University of Virginia
Abstract
The origin of heavy elements synthesized via rapid neutron capture process (rprocess) is one of the longstanding questions in astronomy. So far, the only confirmed astrophysical sites of rprocess nucleosynthesis are neutron star mergers, thanks to the multimessenger detection in 2017. However, there is a another promising site  dying massive stars, or collapsars, which were first invoked as a model to explain long gamma ray bursts. Here, we are going to present our work in modeling the collapsar explosions using 3dimensional general relativistic magnetohydrodynamics simulations.

5:00  6:30 pm EDTReception11th Floor Collaborative Space
Tuesday, July 9, 2024

9:00  9:45 am EDTNeutrino Quantum Kinetics11th Floor Lecture Hall
 Speaker
 Irene Tamborra, University of Copenhagen
 Session Chair
 Giacomo Dimarco, University of Ferrara
Abstract
Neutrinos change their flavor, while propagating in the core of compact astrophysical sources, such as corecollapse supernovae and neutron star mergers. Recent developments on the modeling of neutrino quantum kinetics in compact astrophysical sources, as well as its impact on the stellar dynamics and synthesis of the heavy elements will be reviewed.

10:00  10:30 am EDTCoffee Break11th Floor Collaborative Space

10:30  11:15 am EDTTBA11th Floor Lecture Hall
 Speaker
 Sherwood Richers, University of Tennessee, Knoxville
 Session Chair
 Giacomo Dimarco, University of Ferrara

11:25  11:30 am EDTGroup Photo (Immediately After Talk)11th Floor Lecture Hall

11:30 am  2:00 pm EDTLunch/Free Time

2:00  2:30 pm EDTEfficient numerical methods for the Boltzmann equation11th Floor Lecture Hall
 Speaker
 Giacomo Dimarco, University of Ferrara
 Session Chair
 Irene Tamborra, University of Copenhagen
Abstract
We present a numerical method for solving the unsteady Boltzmann equation describing rarefied gas dynamics flows based on the combination of a wieghted particle approach on a Cartesian lattice and a fast spectral schemes for the collisional integral. We will also discuss the extension of such method to the case of electromagnetic conducting fluids and how to take into account the quantification of uncertainty in these models. Several numerical tests will explore the capability of the scheme proposed in modeling transport phenomena.

2:40  3:10 pm EDTJet launching from binary neutron star mergers: Incorporating neutrino transport and magnetic fields11th Floor Lecture Hall
 Virtual Speaker
 Milton Ruiz, University of Valencia
 Session Chair
 Irene Tamborra, University of Copenhagen
Abstract
We perform general relativistic, magnetohydrodynamic (GRMHD) simulations of merging binary neutron stars incorporating neutrino transport and magnetic fields. Our new radiative transport module for neutrinos adopts a general relativistic, truncatedmoment (M1) formalism. The binaries consist of two identical, irrotational stars modeled by the SLy nuclear equation of state (EOS). They are initially in quasicircular orbit and threaded with a poloidal magnetic field that extends from the stellar interior into the exterior. We insert neutrino processes shortly after the merger and focus on the role of neutrinos in launching a jet following the collapse of the hypermassive neutron star (HMNS) remnant to a spinning black hole (BH). We treat two microphysical versions: one (a ``warmup"") evolving a single neutrino species and considering only chargedcurrent processes, and the other evolving three species $(\nu_e, \bar{\nu}_e, \nu_{\rm x})$ and related processes. We trace the evolution until the system reaches a quasiequilibrium state after BH formation. We find that the BH + disk remnant eventually launches an incipient jet. The electromagnetic Poynting luminosity is $\sim 10^{53} \rm \, erg\, s^{1}$, consistent with that of typical short gammaray bursts (sGRBs). The effect of neutrino cooling shortens the lifetime of the HMNS, and lowers the amplitude of the major peak of the gravitational wave (GW) power spectrum somewhat. After BH formation, neutrinos help clear out the matter near the BH poles, resulting in lower baryonloaded surrounding debris. The neutrino luminosity resides in the range $\sim 10^{5253} \rm \,erg\,s^{1}$ once quasiequilibrium is achieved. Comparing with the neutrinofree models, we observe that the inclusion of neutrinos yields similar ejecta masses and is inefficient in carrying off additional angular momentum.

3:20  3:50 pm EDTCoffee Break11th Floor Collaborative Space

3:50  5:00 pm EDTOpen DiscussionOpen Discussion  11th Floor Lecture Hall
Wednesday, July 10, 2024

9:00  9:30 am EDTTBA11th Floor Lecture Hall
 Speaker
 Elias Most, California Institute of Technology
 Session Chair
 Manuel Izquierdo, University of the Balearic Islands

9:40  9:55 am EDTMultigroup neutrino transport in hypermassive neutron star simulationsShort Talk  11th Floor Lecture Hall
 Speaker
 Patrick ChiKit Cheong, UC Berkeley
 Session Chair
 Somdutta Ghosh, NC State University
Abstract
Energyintegrated twomoment neutrino transport schemes are getting popular in neutron star merger simulations. However, it is still unclear how accurate they are compared to energydependent neutrino transport. In this talk, I will briefly present the key elements of both energyintegrated and energydependent neutrino transport schemes in the GRRMHD code Gmunu. In addition, I will compare the postmerger simulations with these schemes.

10:00  10:30 am EDTCoffee Break11th Floor Collaborative Space

10:30  11:00 am EDTNeutrinos in magnetically driven corecollapse supernovae11th Floor Lecture Hall
 Virtual Speaker
 Martin Obergaulinger, University of Valencia
 Session Chair
 Somdutta Ghosh, NC State University
Abstract
Neutrinos and magnetic fields may play similarly important roles in the collapse and explosion of a subset of massive stars. Determining the explosion mechanism as well as its impact on the nucleosynthesis and the propagation of the ejecta requires longtime simulations. I will present such models performed for several sets of precollapse models and describe the neutrino physics that went into them, including new developments on the minimally implicit time integration of the stiff neutrinomatter interaction terms.

11:10  11:25 am EDTProgenitor dependence of neutrino heating in corecollapse supernovae in 1D, 2D, and 3D: the role of compactnessShort Talk  11th Floor Lecture Hall
 Speaker
 Luca Boccioli, University of California, Berkeley
 Session Chair
 Somdutta Ghosh, NC State University
Abstract
In this talk I will present the progenitor dependence of neutrino heating in the gain region of CCSNe. I will show that progenitors with higher compactness generate more neutrino heating, and therefore result in successful explosions. I will then analyze the interplay between neutrino heating and neutrinodriven convection using a simple semianalytical model. Finally, I will show how some 1D models can be used to produce a similar timedependent neutrino heating in order to achieve an explosion, and compare them to other widely used 1D models that instead use different prescriptions to trigger the explosion.

11:30 am  2:00 pm EDTLunch/Free Time

2:00  2:15 pm EDTA generalrelativistic full Boltzmann solver based on the finite volume methodShort Talk  11th Floor Lecture Hall
 Speaker
 Arthur Offermans, KU Leuven
 Session Chair
 Luca Boccioli, University of California, Berkeley
Abstract
Simulations of astrophysical systems where neutrinos play a significant role, like corecollapse supernovae, would ideally solve the neutrino transport equation fully, i.e. solve the full Boltzmann equation. Because of its very high computational cost (6+1D), simulations generally rely on approximations of the equation that are more affordable. It is however difficult to estimate what is lost through these approximations if we do not have access to a full solution. Solving the full equation would also enable a more accurate study of the impact of neutrinos on the phenomenon that is considered. Therefore, we developed a multidimensional full Boltzmann solver based on the Finite Volume method within the GRMHD simulation code Gmunu in order to perform those more accurate simulations. We present our solver, its performance on some first test cases and compare these results to the M1 radiation transport scheme.

2:20  2:35 pm EDTExpanding the Boltzmann equation to include neutrino flavor evolutionShort Talk  11th Floor Lecture Hall
 Speaker
 Marie Cornelius, University of Copenhagen
 Session Chair
 Luca Boccioli, University of California, Berkeley
Abstract
Neutrinos, despite their weakly interacting nature, play a crucial role in corecollapse supernovae and neutron star mergers. In these dense environments, the neutrino number density is so large that the neutrino coherent forward scattering triggers flavor conversions. In this talk, I will explain how we can expand on the Boltzmann treatment to include neutrino selfinteractions, using a quantumkinetic approach. I will discuss recent developments related to the implications that neutrino quantum kinetics has on the symmetries of the system and the neutrino properties.

2:40  3:10 pm EDTCoffee Break11th Floor Collaborative Space

3:10  3:25 pm EDTTBAShort Talk  11th Floor Lecture Hall
 Speaker
 Somdutta Ghosh, NC State University
 Session Chair
 Luca Boccioli, University of California, Berkeley

3:30  3:45 pm EDTBinary neutron star merger with radiation transport and accurate neutrino microphysicsShort Talk  11th Floor Lecture Hall
 Speaker
 Harry HoYin Ng, Institute for Theoretical Physics, GoetheUniversität Frankfurt
 Session Chair
 Luca Boccioli, University of California, Berkeley
Abstract
We present selfconsistent, generalrelativistic hydrodynamical simulations of binary neutron star mergers. These simulations incorporates the truncated moment radiation transport (M1) method, alongside advanced neutrino physics, particularly focusing on the direct URCA process. Our results underscore the differences between conventional and advanced neutrino microphysics, highlighting their impacts on neutrino cooling, heating, and matter composition.

3:50  5:00 pm EDTOpen DiscussionOpen Discussion  11th Floor Lecture Hall
Thursday, July 11, 2024

9:00  9:30 am EDTClassical Neutrino Kinetics in Core Collapse Supernovae, The Ultimate Goal: Rationale, Requirements, Constraints, Implementations, and Outlook11th Floor Lecture Hall
 Speaker
 Anthony Mezzacappa, University of Tennessee, Knoxville
 Session Chair
 Anna Suliga, University of California, Berkeley
Abstract
It is now well established that neutrinos can drive core collapse supernova explosions and likely do for the lion’s share of observed events in the Universe. They are center stage in the modeling of core collapse supernovae and dominate the computational cost in all realistic models, given the need for a kinetics treatment of neutrino production, transport, and interaction in the cores of massive stars. Neutrino mean free paths range over orders of magnitude, and a fluid description is not accurate except in the innermost regions of these cores. The ultimate classical description of such kinetics would be achieved by solving the Boltzmann kinetic equations for all flavors of neutrinos and antineutrinos produced. Boltzmann kinetics would then provide a sound foundation for the extension to quantum kinetics in order to incorporate neutrino flavor transformations that are expected to occur, which may impact one or all of the following: the explosion mechanism, nucleosynthesis, and terrestrial neutrino signatures. The modeling of neutrino kinetics in core collapse supernovae is compounded by the fact that lepton number and energy must be conserved simultaneously and that the neutrino distribution functions must be bounded given the FermiDirac statistics obeyed by these Fermions. Success in arriving at implementations of Boltzmann neutrino kinetics in future core collapse supernova models will require reformulations of the fundamental equations and the development of discretizations for these equations, that conserve lepton number and energy, are realizable – i.e., maintain boundedness of the neutrino distributions – and are computationally efficient. I will discuss each of these topics, as well as indicate progress to date in achieving our ultimate goal, by our group and others.

9:40  9:55 am EDTGrey relativistic M1 neutrino transport in the BAM code: application to low mass binary neutron star mergerShort Talk  11th Floor Lecture Hall
 Speaker
 Federico Schianchi, University of Potsdam
 Session Chair
 Anna Suliga, University of California, Berkeley
Abstract
Neutrino interactions are essential for an accurate understanding of binary neutron star merger ejecta and postmerger dynamics. We recently extended the infrastructure of the wellestablished numericalrelativity code BAM, that until recently neglected neutrinodriven interactions. We included a firstorder multipolar radiation transport scheme (M1). After testing our implementation on a set of standard scenarios, we applied it to the evolution of lowmass binary systems, and we performed an analysis of ejecta properties. We found an important high electron fraction component of the ejecta, with a persistent wind taking place from the upper face of the disk for the whole duration of the simulation.

10:00  10:30 am EDTCoffee Break11th Floor Collaborative Space

10:30  11:00 am EDTFast Evaluation of the Boltzmann Collision Operator Using Data Driven Reduced Order Models11th Floor Lecture Hall
 Speaker
 Alexander Alekseenko, California State University Northridge
 Session Chair
 Anna Suliga, University of California, Berkeley
Abstract
The kinetic Boltzmann equation models macroscopic behavior of gas by averaging individual molecular interactions. It describes the state of gas using sevendimensional velocity distribution function in three space, three velocity and one temporal variables and is believed to be the most accurate model of noncontinuum gas. The flip side of its descriptive power is that a sevendimensional velocity distribution function is difficult to discretize. As a result, practical solutions of kinetic equations continue to be challenging in three dimensions in complex domains and in applications to complex flows. An additional major difficulty continues to be the evaluation of the multifold integral operator describing the effect of molecular collisions. Low rank tensor approximations emerged recently as a promising approach to reduce effective dimensionality of discrete solutions and accelerate numerical computation of high dimensional problems. Low rank approximations were applied to discretization of the velocity distribution function with some success. At the same time, attempts to compress the collision operator using higher order singular value decomposition usually fail to provide significant savings do the properties of the operator. A possible alternative is the development of reduced order models (ROMs) based on low rank representation of solutions that is specific for the problem at hand. A single evaluation of a ROM for the collision operator requires O(K^3) operation where K is the size of the ROM basis. This becomes prohibitively expensive for K>100 compared to the O(M^2) full rank approaches where M is the total number of discrete velocity points. However, in practice, K<50, and the ROM can provide up to two orders of magnitude of speedup compared to fully discrete methods. Other ideas for compression of kinetic equations include the use of artificial neural networks. In this talk we will introduce ROMs for the kinetic Boltzmann equation as well as other ideas and will highlight our recent work in development of ROMs for solving the Boltzmann equation in zero and one spatial variables.

11:10  11:25 am EDTTowards a General Relativistic Boltzmann Transport for Binary Neutron Star MergersShort Talk  11th Floor Lecture Hall
 Speaker
 Maitraya Bhattacharyya, The Pennsylvania State University
 Session Chair
 Anna Suliga, University of California, Berkeley
Abstract
We present a new neutrino transport code for binary neutron star merger simulations for the numerical relativity code AthenaK. We use finite element and spectral approaches to handle the angular dependence while energy discretization is handled using a finite volume scheme. We employ an asymptoticpreserving discontinuous Galerkin (DG) method for the spatial discretization to ensure correct behavior in the diffusiondominated regime. A semiimplicit time stepping scheme is used to handle the stiff and nonstiff sources correctly. In the first part of the talk we describe the two approaches for angular discretization: the finiteelement method in angle (FEMN) and filtered spherical harmonics (FPN) with an emphasis on positivity preservation for multienergy schemes. We also describe a strategy to obtain the two moments method (M1) from the formulated equations. We then compare the efficacy of the three approaches using various toy problems in the presence of a moving medium and general relativity.

11:30 am  2:00 pm EDTLunch/Free Time

2:00  2:30 pm EDTCorecollapse supernovae as probes of (not only) nonstandard neutrino physics11th Floor Lecture Hall
 Speaker
 Anna Suliga, University of California, Berkeley
 Session Chair
 Federico Schianchi, University of Potsdam
Abstract
Corecollapse supernovae are one of the most complex phenomena in the Universe. Not only are they one of the production sites of the heavy elements that enable the existence of life, but their cores are also one of the densest environments we can probe, albeit indirectly. Corecollapse supernovae are also among the most spectacular and efficient neutrino factories. Detecting these neutrinos can allow us to probe physics in extreme conditions inaccessible on Earth. In this talk, I will discuss how we can prepare for the next nearby supernova neutrino detection to extract as much information as possible from the neutrino signal. I will also talk about how observing neutrinos from all the past collapses in our Universe – the diffuse supernova neutrino background  can help us better understand the supernova population and may provide hints about physics beyond the Standard Model.

2:40  2:55 pm EDTThe Guided Moments formalism: a new neutrino treatmentShort Talk  11th Floor Lecture Hall
 Speaker
 Manuel Izquierdo, University of the Balearic Islands
 Session Chair
 Federico Schianchi, University of Potsdam
Abstract
Accurate modeling of neutrino transport plays a crucial role in understanding astrophysical phenomena such as corecollapse supernovae and neutron star mergers. In this talk, I will review two popular methods for approximating the sevendimensional Boltzmann equation: the truncated momentum formalism (M1 scheme) and MonteCarlo (MC) algorithms. Then, I wil present the Guided Moment (GM) formalism, which combines efficiently both methods to capture accurately both optically thick and thin limits. A comparison between the three schemes (GM, M1, MC) will demonstrate the tremendous potential of the GM formalism.

3:00  3:20 pm EDTCoffee Break11th Floor Collaborative Space

3:20  3:50 pm EDTGrey Neutrino Transport in CoreCollapse Supernovae11th Floor Lecture Hall
 Speaker
 Evan O'Connor, Stockholm University
 Session Chair
 Federico Schianchi, University of Potsdam
Abstract
In this talk, I will share our recent work in developing a grey neutrino transport algorithm based on the M1 formalism for use in corecollapse supernovae (Andresen et al. 2024). We extensively compare with 1D and 2D simulations from various transport codes as well as our own energydependent M1 code. We see significant speed up compared to the energy dependent version (45 times faster) with only slight degradation in the neutrino signal and the dynamics. I'll also share some other recent work by the Stockholm group.

4:00  5:00 pm EDTPanel Discussion IPanel Discussion  11th Floor Lecture Hall
Friday, July 12, 2024

9:00  9:30 am EDTA MonteCarlo based relativistic neutrino radiation hydrodynamics simulation for blackhole disk systems11th Floor Lecture Hall
 Speaker
 Kyohei Kawaguchi, Max Planck Institute for Gravitational Physics (AEI, PotsdamGolm)
 Session Chair
 Shane Davis, University of Virginia
Abstract
Accurately solving neutrino radiation is a key ingredient for the quantitative understanding of the postmerger physics of neutron star binaries. For this purpose, we develop a new relativistic neutrino radiation hydrodynamics code based on the MonteCarlo algorithm employing our scheme to achieve the secondorder accuracy in time. In particular, in this code, neutrino/antineutrino pair process including electrontype neutrinos is dynamically taken into account. In the talk, we'll demonstrate that our code reproduces thermal equilibrium states in a wide range of setups in the physically correct manner. We'll then show our preliminary results applying our code to blackhole disk systems formed in neutron star binary mergers.

9:40  10:00 am EDTCoffee Break11th Floor Collaborative Space

10:00  10:30 am EDTAnalytic Closures for M1 Neutrino Transport11th Floor Lecture Hall
 Speaker
 Lena Murchikova, Northwestern University
 Session Chair
 Manuel Izquierdo, University of the Balearic Islands
Abstract
Carefully accounting for neutrino transport is an essential component of many astrophysical studies. Solving the full transport equation is too expensive for most realistic applications, especially those involving multiple spatial dimensions. Resorting to approximations is often the only viable option for obtaining solutions. One such approximation is the M1 method. It utilizes the system of the lowest two moments of the transport equation and closes the system with an ad hoc closure relation. The accuracy of the M1 solution depends on the quality of the closure. I will discuss an extensive study of these closures we carried out a few years ago by comparing the results of M1 calculations with precise Monte Carlo calculations of the radiation field around sphericallysymmetric protoneutron star models. We find that no closure performs consistently better or worse than others in all cases. The level of accuracy a given closure yields depends on the matter configuration, neutrino type, and neutrino energy. Given this limitation, we concluded that the maximum entropy closure by Minerbo (1978) yields relatively accurate results in the broadest set of cases considered in this work.

10:40  10:55 am EDTControl of Instability in a VlasovPoisson System Through External Electric FieldShort Talk  11th Floor Lecture Hall
 Speaker
 Yukun Yue, University of Wisconsin, Madison
 Session Chair
 Manuel Izquierdo, University of the Balearic Islands
Abstract
The VlasovPoisson equation serves as a fundamental model for simulating plasma dynamics. Within this framework, there exist two equilibrium states that are inherently unstable, namely the TwoStream and BumponTail instabilities. Suppressing these instabilities is often a desirable objective in numerous practical applications. This paper aims to achieve such suppression by the implementation of an external field. When minor perturbations are introduced into these equilibrium states, they have the potential to instigate rapid growth, resulting in substantial disruptions of the equilibrium. To address this challenge, we introduce two distinct strategies for applying an external field to stabilize these inherently unstable distributions. The first strategy focuses on neutralizing the electric field generated within the plasma system. This approach effectively restricts the movement of the particles in a freedrifting state. The second strategy adopts a more comprehensive approach, leveraging linear analysis to investigate various methods for the application of the external field, inclusive of the first method. We provide numerical evidence to substantiate the efficacy of these proposed methodologies.

11:00  11:15 am EDTStability of postmergerlike neutron starsShort Talk  11th Floor Lecture Hall
 Speaker
 Nishad Muhammed, Washington State University
 Session Chair
 Manuel Izquierdo, University of the Balearic Islands
Abstract
Binary neutron star mergers produce massive, hot, rapidly differentially rotating neutron star remnants; electromagnetic and gravitational wave signals associated with the subsequent evolution depend on the stability of these remnants. Stability of relativistic stars has previously been studied for uniform rotation and a class of differential rotation with monotonic angular velocity profiles. Stability of those equilibria to axisymmetric perturbations was found to respect a turning point criterion: along a constant angular momentum sequence, the onset of unstable stars is found at maximum density less than but close to the density of maximum mass. We test this turning point criterion for nonmonotonic angular velocity profiles and nonisentropic entropy profiles, both chosen to more realistically model postmerger equilibria. Stability is assessed by evolving perturbed equilibria in 2D using the Spectral Einstein Code. We confirm the turning point theorem and determine the region of our rotation law parameter space that provides highest maximum mass for a given angular momentum.

11:20  11:35 am EDTMagnetized winds from low mass BNS binariesShort Talk  11th Floor Lecture Hall
 Speaker
 Carlo Musolino, Goethe University Frankfurt
 Session Chair
 Manuel Izquierdo, University of the Balearic Islands
Abstract
A significant interest has emerged in assessing whether collimated and ultrarelativistic outflows can be produced by a longlived remnant formed after a binary neutronstar (BNS) merger. To clarify some of the aspects of this process, we report the results of longterm stateoftheart generalrelativistic neutrinomagnetohydrodynamics simulations of the inspiral and merger of a magnetized BNS system. We find that after an initial phase of MRIdriven growth of the magnetic field in the torus, the field breaks out due to a Parkertype instability leading to a magnetically driven, mildly relativistic polar wind.

11:40 am  2:00 pm EDTLunch/Free Time

2:00  3:00 pm EDTPanel Discussion IIPanel Discussion  11th Floor Lecture Hall

3:00  3:30 pm EDTCoffee Break11th Floor Collaborative Space
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 Personal car travel to ICERM from outside New England
 Multipledestination plane ticket; does not include layovers to reach ICERM
 Arriving or departing from ICERM more than a day before or day after the program
 Multiple trips to ICERM
 Rental car to/from ICERM
 Flights on a Swiss, Japanese, or Australian airlines
 Arriving or departing from airport other than PVD/BOS or home institution's local airport
 2 oneway plane tickets to create a roundtrip (often purchased from Expedia, Orbitz, etc.)
 Travel Maximum Contributions

 New England: $350
 Other contiguous US: $850
 Asia & Oceania: $2,000
 All other locations: $1,500
 Note these rates were updated in Spring 2023 and superseded any prior invitation rates. Any invitations without travel support will still not receive travel support.
 Reimbursement Requests

Request Reimbursement with Cube
Refer to the back of your ID badge for more information. Checklists are available at the front desk and in the Reimbursement section of Cube.
 Reimbursement Tips

 Scanned original receipts are required for all expenses
 Airfare receipt must show full itinerary and payment
 ICERM does not offer per diem or meal reimbursement
 Allowable mileage is reimbursed at prevailing IRS Business Rate and trip documented via pdf of Google Maps result
 Keep all documentation until you receive your reimbursement!
 Reimbursement Timing

6  8 weeks after all documentation is sent to ICERM. All reimbursement requests are reviewed by numerous central offices at Brown who may request additional documentation.
 Reimbursement Deadline

Submissions must be received within 30 days of ICERM departure to avoid applicable taxes. Submissions after thirty days will incur applicable taxes. No submissions are accepted more than six months after the program end.