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SUMMARY:Viscous fluid dynamics for binary neutron-star mergers
DTSTART;VALUE=DATE-TIME:20191104T094000Z
DTEND;VALUE=DATE-TIME:20191104T100000Z
DTSTAMP;VALUE=DATE-TIME:20200228T154249Z
UID:indico-contribution-3549011@indico.cern.ch
DESCRIPTION:Speakers: Jorge Noronha (University of Sao Paulo)\nThe recent
detection of a binary neutron star merger using gravitational waves and el
ectromagnetic signals marked the dawn of the multi-messenger astronomy era
. Such events are expected to provide key information about the properties
of matter at extreme densities and temperatures and\, for many years\, it
was assumed that this system could be reasonably described as an ideal (i
.e. inviscid) fluid coupled to Einsteinâ€™s equations. This was recently r
evisited by Alford et al. in [1] using state-of-the-art merger simulations
which showed that damping of high-amplitude oscillations due to bulk visc
osity is expected to play an important role in gravitational wave emission
and\, as such\, this should be taken into account and thoroughly investig
ated in realistic merger simulations. However\, viscous effects have not y
et been included in merger simulations because this requires a formulation
of relativistic fluid dynamics\, including bulk viscosity\, that is causa
l in the strong nonlinear regime probed by the mergers. This has been an o
pen problem in the field since Israel and Stewart's seminal work in 1979.
In this work we solve this problem and prove [2] that the Einstein-Israel-
Stewart equations\, describing the dynamics of a relativistic fluid with b
ulk viscosity and nonzero baryon charge dynamically coupled to gravity\, a
re causal in the full nonlinear regime. We use an arbitrary equation of st
ate and do not make any simplifying symmetry or near-equilibrium assumptio
n\, requiring only physically natural conditions on the fields. These resu
lts pave the way for the inclusion of bulk viscosity effects in simulation
s of gravitational-wave signals coming from neutron star mergers\, which w
ill provide key information about the novel out-of-equilibrium properties
of highly dense QCD matter in neutron stars.\n\n[1] M.G. Alford\, L. Bovar
d\, M. Hanauske\, L. Rezzolla and K. Schwenzer\,\n ``Viscous Dissipation
and Heat Conduction in Binary Neutron-Star Mergers\,''\n Phys. Rev. Lett.
120\, no. 4\, 041101 (2018).\n\n[2] F. S. Bemfica\, M. M. Disconzi and J
. Noronha\,\n ``Causality of the Einstein-Israel-Stewart Theory with Bulk
Viscosity\,''\n Phys. Rev. Lett. 122\, no. 22\, 221602 (2019).\n\nhttps
://indico.cern.ch/event/792436/contributions/3549011/
LOCATION:Wanda Han Show Theatre & Wanda Reign Wuhan Hotel
URL:https://indico.cern.ch/event/792436/contributions/3549011/
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