402 research outputs found
What the Timing of Millisecond Pulsars Can Teach us about Their Interior
The cores of compact stars reach the highest densities in nature and
therefore could consist of novel phases of matter. We demonstrate via a
detailed analysis of pulsar evolution that precise pulsar timing data can
constrain the star's composition, through unstable global oscillations
(r-modes) whose damping is determined by microscopic properties of the
interior. If not efficiently damped, these modes emit gravitational waves that
quickly spin down a millisecond pulsar. As a first application of this general
method, we find that ungapped interacting quark matter is consistent with both
the observed radio and x-ray data, whereas for ordinary nuclear matter some
additional enhanced damping mechanism is required.Comment: 6 pages, 5 figures, version to be published in PR
Low Energy Dynamics in Ultradegenerate QCD Matter
We study the low energy behavior of QCD Green functions in the limit that the
baryon chemical potential is much larger than the QCD scale parameter
. We show that there is a systematic low energy expansion in
powers of , where is the energy and is the
screening scale. This expansion is valid even if the effective quark-gluon
coupling is not small. The expansion is purely perturbative in the magnetic
regime . If the external momenta and energies satisfy , planar, abelian ladder diagrams involving the full quark
propagator have to be resummed but the corresponding Dyson-Schwinger equations
are closed.Comment: 4 pages, published versio
Impact of r-modes on the cooling of neutron stars
Studying the frequency and temperature evolution of a compact star can give
us valuable information about the microscopic properties of the matter inside
the star. In this paper we study the effect of dissipative reheating of a
neutron star due to r-mode oscillations on its temperature evolution. We find
that there is still an impact of an r-mode phase on the temperature long after
the star has left the instability region and the r-mode is damped completely.
With accurate temperature measurements it may be possible to detect this trace
of a previous r-mode phase in observed pulsars.Comment: 7 pages, 5 figures, Proceedings of QCD@work 2012 International
Workshop on QCD Theory and Experimen
Suprathermal viscosity of dense matter
Motivated by the existence of unstable modes of compact stars that eventually
grow large, we study the bulk viscosity of dense matter, taking into account
non-linear effects arising in the large amplitude regime, where the deviation
mu_Delta of the chemical potentials from chemical equilibrium fulfills mu_Delta
> T. We find that this supra-thermal bulk viscosity can provide a potential
mechanism for saturating unstable modes in compact stars since the viscosity is
strongly enhanced. Our study confirms previous results on strange quark matter
and shows that the suprathermal enhancement is even stronger in the case of
hadronic matter. We also comment on the competition of different weak channels
and the presence of suprathermal effects in various color superconducting
phases of dense quark matter.Comment: 8 page
Phase conversion dissipation in multicomponent compact stars
We propose a mechanism for the damping of density oscillations in
multicomponent compact stars. The mechanism is the periodic conversion between
different phases, i.e., the movement of the interface between them, induced by
pressure oscillations in the star. The damping grows nonlinearly with the
amplitude of the oscillation. We study in detail the case of r-modes in a
hybrid star with a sharp interface, and we find that this mechanism is powerful
enough to saturate the r-mode at very low saturation amplitude, of order
, and is therefore likely to be the dominant r-mode saturation
mechanism in hybrid stars with a sharp interface.Comment: 17 pages, 8 figures. Typos in Eq. (15), Eqs. (64)-(65) and Eqs.
(B4)-(B5) correcte
Large amplitude behavior of the bulk viscosity of dense matter
We study the bulk viscosity of dense matter, taking into account non-linear
effects which arise in the large amplitude "supra-thermal" region where the
deviation of the chemical potentials from chemical equilibrium
fulfills . This regime is relevant to unstable modes such as
r-modes, which grow in amplitude until saturated by non-linear effects. We
study the damping due to direct and modified Urca processes in hadronic matter,
and due to nonleptonic weak interactions in strange quark matter. We give
general results valid for an arbitrary equation of state of dense matter and
find that the viscosity can be strongly enhanced by supra-thermal effects. Our
study confirms previous results on quark matter and shows that the non-linear
enhancement is even stronger in the case of hadronic matter. Our results can be
applied to calculations of the r-mode-induced spin-down of fast-rotating
neutron stars, where the spin-down time will depend on the saturation amplitude
of the r-modeComment: 15 pages, 11 figure
Signatures for quark matter from multi-messenger observations
We review the prospects for detecting quark matter in neutron star cores. We
survey the proposed signatures and emphasize the importance of data from
neutron star mergers, which provide access to dynamical properties that operate
on short timescales that are not probed by other neutron star observables.Comment: 23 pages, 4 figures; refs. added, accepted for publicatio
Bridging the gap by shaking superfluid matter
In cold compact stars, Cooper pairing between fermions in dense matter leads
to the formation of a gap in their excitation spectrum and typically
exponentially suppresses transport properties. However, we show here that weak
Urca reactions become strongly enhanced and approach their ungapped level when
the star undergoes density oscillations of sufficiently large amplitude. We
study both the neutrino emissivity and the bulk viscosity due to direct Urca
processes in hadronic, hyperonic and quark matter and discuss different
superfluid and superconducting pairing patterns.Comment: 5 pages, 4 figure
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