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I consider a simple set of equations that govern the expansion of boost-invariant plasmas of massless particles. These equations describe the transition from a collisionless regime at early time to hydrodynamics at late time. Their…

Nuclear Theory · Physics 2023-09-26 Jean-Paul Blaizot

We obtain equations of motion for the boost-invariant expansion of a system of chiral particles. Our analysis is based on the Boltzmann equation for left- and right-handed massless particles in the relaxation time approximation. We assume…

High Energy Physics - Phenomenology · Physics 2024-02-15 Nora Weickgenannt , Jean-Paul Blaizot

We establish a complete set of hydrodynamic equations for a spin-1 Bose-Einstein condensate (BEC), which are equivalent to the multi-component Gross-Pitaevskii equations and expressed in terms of only observable physical quantities: the…

Quantum Gases · Physics 2015-06-11 Emi Yukawa , Masahito Ueda

We derive a formulation of relativistic spin hydrodynamics with totally antisymmetric spin tensors that satisfy the Frenkel-Mathisson-Pirani condition. In our proposed spin hydrodynamics, the second law of thermodynamics is fulfilled by the…

Nuclear Theory · Physics 2025-06-27 Shuo Fang , Kenji Fukushima , Shi Pu , Dong-Lin Wang

We show that the boost-invariant and cylindrically asymmetric hydrodynamic equations for baryon-free matter may be rewritten as only two coupled partial differential equations. In the case where the system exhibits the cross-over phase…

Nuclear Theory · Physics 2007-05-23 Mikolaj Chojnacki

In this paper we present the details of our previous work on exact solutions in second-order conformal hydrodynamics together with a number of new solutions found by mapping Minkowski space onto various curved spacetimes such as anti-de…

High Energy Physics - Theory · Physics 2014-06-18 Yoshitaka Hatta , Jorge Noronha , Bo-Wen Xiao

A numerical algorithm for the implementation of anisotropic distributions in the frame of the relativistic Boltzmann equation is presented. The implementation relies on the expansion of the Romatschke-Strickland distribution with respect to…

Nuclear Theory · Physics 2019-02-06 Victor E. Ambrus , Calin Guga-Rosian

We present a new solution of relativistic hydrodynamics in 1+3 dimensions which depends on both the transverse coordinate and rapidity. At early times the flow expands dominantly longitudinally in a non-boost-invariant manner, and at late…

High Energy Physics - Phenomenology · Physics 2016-02-03 Yoshitaka Hatta , Bo-Wen Xiao , Di-Lun Yang

Based on the Wigner function in local equilibrium, we derive hydrodynamical quantities for a system of polarized spin-1/2 particles: the particle number current density, the energy-momentum tensor, the spin tensor, and the dipole moment…

High Energy Physics - Theory · Physics 2021-12-22 Hao-Hao Peng , Jun-Jie Zhang , Xin-Li Sheng , Qun Wang

We investigate the boost-invariant expansion of a recently developed first-order spin hydrodynamic framework in which the spin chemical potential is treated as a leading-order hydrodynamic variable. Considering a symmetric energy-momentum…

Nuclear Theory · Physics 2026-04-07 Sejal Singh , Sourav Dey , Arpan Das , Hiranmaya Mishra , Amaresh Jaiswal

We develop Hamiltonian mechanics on Aristotelian manifolds, which lack local boost symmetry and admit absolute time and space structures. We construct invariant phase space dynamics, define free Hamiltonians, and establish a generalized…

Statistical Mechanics · Physics 2025-12-03 Andrea Amoretti , Daniel K. Brattan , Luca Martinoia

We compute finite coupling correction to a nonlinear second order hydrodynamic coefficient in the boost invariant expansion of the N=4 supersymmetric Yang-Mills plasma. The result is universal for a large class of strongly coupled four…

High Energy Physics - Theory · Physics 2009-01-14 Alex Buchel , Miguel Paulos

We study the longitudinal spin polarization of a relativistic fluid of massive spin-1/2 particles undergoing a boost-invariant expansion in the longitudinal direction and rotating in the transverse plane. We express the polarization vector…

Nuclear Theory · Physics 2025-03-18 Nora Weickgenannt , Jean-Paul Blaizot

Recent progress in the formulation of relativistic hydrodynamics for particles with spin one-half is reviewed. We start with general arguments advising introduction of a tensor spin chemical potential that plays a role of the Lagrange…

Nuclear Theory · Physics 2019-09-09 Wojciech Florkowski , Radoslaw Ryblewski , Avdhesh Kumar

The Boltzmann equation is solved in the relaxation time approximation using a hierarchy of angular moments of the distribution function. Our solution is obtained for an azimuthally symmetric radially expanding boost-invariant conformal…

Nuclear Theory · Physics 2020-06-24 Ashutosh Dash , Victor Roy

Four formulations of perfect spin hydrodynamics for spin-1/2 particles, distinguished by their treatment of spin (classical vs. quantum) and by the underlying particle statistics (Boltzmann vs. Fermi-Dirac), are analyzed and shown to…

High Energy Physics - Phenomenology · Physics 2025-11-25 Samapan Bhadury , Zbigniew Drogosz , Wojciech Florkowski , Sudip Kumar Kar , Valeriya Mykhaylova

We critically compare thermodynamic and kinetic approaches, that have been recently used to study relations between the spin polarization and fluid vorticity in systems consisting of spin-one-half particles. The thermodynamic approach…

High Energy Physics - Phenomenology · Physics 2018-10-31 Wojciech Florkowski , Avdhesh Kumar , Radoslaw Ryblewski

A simple exactly solvable kinetic model for the non-linear inelastic hard sphere Boltzmann equation is used to explore the relevance of hydrodynamics for a granular gas. The equation predicts a non-trivial homogeneous cooling state (HCS),…

Soft Condensed Matter · Physics 2007-05-23 Aparna Baskaran , James W. Dufty

We derive a retained-spin micropolar hydrodynamic closure from the Boltzmann--Curtiss equation using a generalized Chapman--Enskog construction in which the local mean spin is retained as a quasi-slow variable. Starting from the…

Soft Condensed Matter · Physics 2026-05-19 Satori Tsuzuki

We use advances in the formalism of boost agnostic passive fluids to constrain transport in polar active fluids, which are subsequently described by the Toner-Tu equations. Acknowledging that the system fundamentally breaks boost symmetry…

Statistical Mechanics · Physics 2024-11-13 Andrea Amoretti , Daniel K. Brattan , Luca Martinoia