15,332 research outputs found
Zero-temperature TAP equations for the Ghatak-Sherrington model
The zero-temperature TAP equations for the spin-1 Ghatak-Sherrington model
are investigated. The spin-glass energy density (ground state) is determined as
a function of the anisotropy crystal field for a large number of spins.
This allows us to locate a first-order transition between the spin-glass and
paramagnetic phases within a good accuracy. The total number of solutions is
also determined as a function of .Comment: 11 pages, 2 ps figures include
Effects of Random Biquadratic Couplings in a Spin-1 Spin-Glass Model
A spin-1 model, appropriated to study the competition between bilinear
(J_{ij}S_{i}S_{j}) and biquadratic (K_{ij}S_{i}^{2}S_{j}^{2}) random
interactions, both of them with zero mean, is investigated. The interactions
are infinite-ranged and the replica method is employed. Within the
replica-symmetric assumption, the system presents two phases, namely,
paramagnetic and spin-glass, separated by a continuous transition line. The
stability analysis of the replica-symmetric solution yields, besides the usual
instability associated with the spin-glass ordering, a new phase due to the
random biquadratic couplings between the spins.Comment: 16 pages plus 2 ps figure
Gravitational waves from pulsars with measured braking index
We study the putative emission of gravitational waves (GWs) in particular for
pulsars with measured braking index. We show that the appropriate combination
of both GW emission and magnetic dipole brakes can naturally explain the
measured braking index, when the surface magnetic field and the angle between
the magnetic dipole and rotation axes are time dependent. Then we discuss the
detectability of these very pulsars by aLIGO and the Einstein Telescope. We
call attention to the realistic possibility that aLIGO can detect the GWs
generated by at least some of these pulsars, such as Vela, for example.Comment: 6 pages and 4 figure
Coalescence Rate of Supermassive Black Hole Binaries Derived from Cosmological Simulations: Detection Rates for LISA and ET
The coalescence history of massive black holes has been derived from
cosmological simulations, in which the evolution of those objects and that of
the host galaxies are followed in a consistent way. The present study indicates
that supermassive black holes having masses greater than underwent up to 500 merger events along their history. The derived
coalescence rate per comoving volume and per mass interval permitted to obtain
an estimate of the expected detection rate distribution of gravitational wave
signals ("ring-down") along frequencies accessible by the planned
interferometers either in space (LISA) or in the ground (Einstein). For LISA,
in its original configuration, a total detection rate of about is
predicted for events having a signal-to-noise ratio equal to 10, expected to
occur mainly in the frequency range . For the Einstein gravitational
wave telescope, one event each 14 months down to one event each 4 years is
expected with a signal-to-noise ratio of 5, occurring mainly in the frequency
interval . The detection of these gravitational signals and their
distribution in frequency would be in the future an important tool able to
discriminate among different scenarios explaining the origin of supermassive
black holes.Comment: 18 pages, 7 figures, to appear in the IJMP
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