Transcript The high density QCD phase transition in compact stars

The high density QCD phase
transition in compact stars
Giuseppe Pagliara
Institut für Theoretische Physik
Heidelberg, Germany
Excited QCD 2010, Tatra National Park, Slovakia
Motivation: the QCD phase diagram
low coupling
Lattice QCD
neutron star densities (core): 10-1 to 10n0 (2x1015gr/cm3),
excellent tools to test properties of matter at extreme
conditions
Quarkyonic
low coupling μ ~ 1.5
GeV nB ~ 200 n0
too large for
two phenomenological models: low density/temperature
neutron stars !
hadronic model and high density/temperature quark
model (MIT bag, NJL, CDM...). Fixing the parameters in
one point of the T-n plane.
Search of Quark matter in violent phenomena of
the Universe: Supernovae and GRBs
Explosion of massive stars
M > 8 Msun, Last close
explosion SN1987 (50
kpc), E = 1053 ergs,
optical signal +
Some SN (Collapsar)
responsible for the emission
of Gamma-Ray-Bursts
t ~ few seconds later
Protoneutron stars deleptonization
path is the phase diagram ?
from A. Steiner PhD-thesis
Ruster et al hep-ph/0509073
t ~ few 106 years later
Neutron stars mergers
Signals:
1) neutrinos
2) Short GRB
3) Gravitational
Waves
4) Cosmic rays:
strangelts
Bauswein et al. 0910.5169
Supernova Explosion
•
Begins with gravitational
collapse of massive stars
(M>8 Msun)
Standard core collapse scenario:
1)
the core collapses to nuclear
density till repulsion due to
nuclear force halts the
collapse
2) Bounce of the inner core and
formation of a shock wave
3) “Old model”: the shock
reverses the infall and
ejects the stellar envelope
leaving behind a
protoneutron star
from T.Janka, Nature Phys. 2005
... but: in all simulations, due to the dissociation of heavy nuclei the shock looses
energy and develops into a standing accretion shock, the “prompt mechanism ”
does not work
Janka (2008)
Quark matter in compact stars
• QCD phase diagram:
first order phase
transition at high
density
• Mass ~ 1.4 solar
masses and Radius ~
10 km
• The central density in
a compact star can
reach values up to ten
times the nuclear
matter saturation
density
from F. Weber
Nuclear matter EoS
three different approaches:
1)
relativistic mean field model (Walecka type models see Müller Serot 1996)
2)
many body - microscopic nucleon-nucleon interactions (with also three body forces, see
van Dalen-Fuchs-Faessler 2004)
3)
chiral models (see Papazoglou et al 1999)
RMF
Nuclear interaction realized by the exchange of mesons ,, (also Hyperons can be
included). Mean field approximation: the meson fields are assumed to be uniform.
5 parameters: 3 mesons/nucleons couplings + 2 for the potential of the  fixed by 5 known
properties of nuclear matter: saturation density, binding energy, incompressibility, effective
mass of nucleon and symmetry energy at saturation
Nuclear matter in compact stars
two conserved charges
beta stability
charge neutrality
Thermodynamic potential
Dispersion relations
Glendenning, Compact stars,1997
particle
Pressure vs
fractions
baryon density
only one independent
chemical potential!
Quark matter EoS: MIT bag model
• modelling of confinement:
1) free or weekly
interacting quarks in a
finite volume, the Bag
2) confinement is provided
by the vacuum pressure B
beta stability
charge neutrality
parameters: current quark masses mu and md few MeV and ms~ 100
MeV and B^1/4 145-200 MeV (+ s corrections)
Matching the EoSs: Gibbs construction
• Gibbs construction: two components system (baryon and
electric charge), global charge neutrality
(Schertler et al. 1998)
- quark volumue fraction, two critical
chemical potentials =0,1
- the pressure changes in the mixed
phase, possible existence of mixed
phase in compact stars !!
Quark matter during the early post bounce phase
(Sagert, Fischer, Hempel, Pagliara, Schaffner-Bielich, Tielemann, Mezzacappa & Liebendörfer
Phys.Rev.Lett. 2009)
Small value of the
Bag, beta equilibrium
μd = μs, high T and low
proton fraction Yp favor
Quark matter
early onset of phase transition in Supernovae !
“Hybrid”equation of state for HIC matter
• production of Quark
matter at low T and
high density unfavored
in HIC:
1) no net strangeness
production
2) isospin symmetric
nuclear matter is soft
The shock wave formation
see also Gentile et al. 1993
The neutrino signal
• the shock propagates into
deleptonized hadronic matter,
Ye=0.1, the matter is shockheated and the electron
degeneracy is lifted, weak
equilibrium restored at Ye > 0.2
• When the shock reaches the
neutrino sphere a second burst
(the first being the
neutronization burst during
bounce ) of all neutrinos is
released dominated by eantineutrinos stemming from
the positron capture that
established the increase in Ye
Explosion energy, masses of PNS and Bag constant
dependence
•
two models with B1/4 =162 and 165
MeV, two progenitor masses 10
and 15 Msun
Larger Bag:
-)Longer proto neutron star accretion
time due to higher critical density
-)More massive proto neutron star with
deeper gravitational potential
-)Stronger second shock and larger
explosion energies
-)Second neutrino burst 100 ms later
with larger peak luminosities
More massive progenitor: earlier onset
of phase transition and more massive
proto neutron star
Properties of second shock
(onset and strength) and
second neutrino burst (time
delay and luminosity) related to
the critical density (Bag).
Detectability
IceCube, SN events
within 50 kpc
SuperK, SN events
within 20 kpc
Dasgupta et al. 0912.2568
Conclusions & outlook
• The dynamics of the formation of quark matter in compact stars might
provide clear signatures in the neutrino signal (measurable in SuperK &
IceCube). Possible mechanism for supernova explosions !!!
Assumptions: first order phase transition at low density
for SN matter!
• Problem1 “experimental test” : low event rate (2-3
supernovae per galaxy per century!!).
• Problem2 “theoretical test”: how long will LQCD need to
study SN matter ?
In the meantime:
• Better idea to model the phase transition? one
Lagrangian with quark degrees of freedom
(NJL-like, nucleon as quark-diquark system, Bentz-Thomas (2001), RezaeianPirner (2006), now also with color superconductivity ..., Dyson-Schwinger...)
Appendix
When Quark matter is eventually
formed?
Pons et al. PRL 2001