22,778 research outputs found
Observing the Galaxy's massive black hole with gravitational wave bursts
An extreme-mass-ratio burst (EMRB) is a gravitational wave signal emitted
when a compact object passes through periapsis on a highly eccentric orbit
about a much more massive object, in our case a stellar mass object about a
10^6 M_sol black hole. EMRBs are a relatively unexplored means of probing the
spacetime of massive black holes (MBHs). We conduct an investigation of the
properties of EMRBs and how they could allow us to constrain the parameters,
such as spin, of the Galaxy's MBH. We find that if an EMRB event occurs in the
Galaxy, it should be detectable for periapse distances r_p < 65 r_g for a \mu =
10 M_sol orbiting object, where r_g = GM/c^2 is the gravitational radius. The
signal-to-noise ratio scales as \rho ~ -2.7 log(r_p/r_g) + log(\mu/M_sol) +
4.9. For periapses r_p < 10 r_g, EMRBs can be informative, and provide good
constraints on both the MBH's mass and spin. Closer orbits provide better
constraints, with the best giving accuracies of better than one part in 10^4
for both the mass and spin parameter.Comment: 25 pages, 17 figures, 1 appendix. One more typo fixe
Expectations for extreme-mass-ratio bursts from the Galactic Centre
When a compact object on a highly eccentric orbit about a much more massive
body passes through periapsis it emits a short gravitational wave signal known
as an extreme-mass-ratio burst (EMRB). We consider stellar mass objects
orbiting the massive black hole (MBH) found in the Galactic Centre. EMRBs
provide a novel means of extracting information about the MBH; an EMRB from the
Galactic MBH could be highly informative regarding the MBH's mass and spin if
the orbital periapsis is small enough. However, to be a useful astronomical
tool EMRBs must be both informative and sufficiently common to be detectable
with a space-based interferometer. We construct a simple model to predict the
event rate for Galactic EMRBs. We estimate there could be on average ~2 bursts
in a two year mission lifetime for LISA. Stellar mass black holes dominate the
event rate. Creating a sample of 100 mission realisations, we calculate what we
could learn about the MBH. On average, we expect to be able to determine the
MBH mass to ~1% and the spin to ~0.1 using EMRBs.Comment: 22 pages, 5 figures, 2 appendices. Minor changes to reflect published
versio
High-Order Adiabatic Approximation for Non-Hermitian Quantum System and Complexization of Berry's Phase
In this paper the evolution of a quantum system drived by a non-Hermitian
Hamiltonian depending on slowly-changing parameters is studied by building an
universal high-order adiabatic approximation(HOAA) method with Berry's phase
,which is valid for either the Hermitian or the non-Hermitian cases. This
method can be regarded as a non-trivial generalization of the HOAA method for
closed quantum system presented by this author before. In a general situation,
the probabilities of adiabatic decay and non-adiabatic transitions are
explicitly obtained for the evolution of the non-Hermitian quantum system. It
is also shown that the non-Hermitian analog of the Berry's phase factor for the
non-Hermitian case just enjoys the holonomy structure of the dual linear bundle
over the parameter manifold. The non-Hermitian evolution of the generalized
forced harmonic oscillator is discussed as an illustrative examples.Comment: ITP.SB-93-22,17 page
Neutrino Scattering in Heterogeneous Supernova Plasmas
Neutrinos in core collapse supernovae are likely trapped by neutrino-nucleus
elastic scattering. Using molecular dynamics simulations, we calculate neutrino
mean free paths and ion-ion correlation functions for heterogeneous plasmas.
Mean free paths are systematically shorter in plasmas containing a mixture of
ions compared to a plasma composed of a single ion species. This is because
neutrinos can scatter from concentration fluctuations. The dynamical response
function of a heterogeneous plasma is found to have an extra peak at low
energies describing the diffusion of concentration fluctuations. Our exact
molecular dynamics results for the static structure factor reduce to the Debye
Huckel approximation, but only in the limit of very low momentum transfers.Comment: 11 pages, 13 figure
Extreme-mass-ratio-bursts from extragalactic sources
Extreme-mass-ratio bursts (EMRBs) are a class of potentially interesting gravitational wave signals. They are produced when a compact object passes through periapsis on a highly eccentric orbit about a much more massive object; we consider stellar mass objects orbiting the massive black holes (MBHs) found in galactic centres. Such a system may emit many EMRBs before eventually completing the inspiral. There are several nearby galaxies that could yield detectable bursts. For a space-borne interferometer like the Laser Interferometer Space Antenna, sensitivity is greatest for EMRBs from MBHs of ∼106–107 M⊙, which could be detected out to ∼100 Mpc. Considering the examples of M32, NGC 4945 and NGC 4395 we investigate if extragalactic EMRB signals can provide information about their sources. This is possible, but only if the periapse radius of the orbit is small, of the order of rp ≲ 8rg, where rg = GM c− 2 is the gravitational radius of the MBH. This limits the utility of EMRBs as an astronomical tool. However, if we are lucky, we could place constraints on the mass and spin of nearby MBHs with 1 per cent precision
Geometric gauge potentials and forces in low-dimensional scattering systems
We introduce and analyze several low-dimensional scattering systems that
exhibit geometric phase phenomena. The systems are fully solvable and we
compare exact solutions of them with those obtained in a Born-Oppenheimer
projection approximation. We illustrate how geometric magnetism manifests in
them, and explore the relationship between solutions obtained in the diabatic
and adiabatic pictures. We provide an example, involving a neutral atom dressed
by an external field, in which the system mimics the behavior of a charged
particle that interacts with, and is scattered by, a ferromagnetic material. We
also introduce a similar system that exhibits Aharonov-Bohm scattering. We
propose some practical applications. We provide a theoretical approach that
underscores universality in the appearance of geometric gauge forces. We do not
insist on degeneracies in the adiabatic Hamiltonian, and we posit that the
emergence of geometric gauge forces is a consequence of symmetry breaking in
the latter.Comment: (Final version, published in Phy. Rev. A. 86, 042704 (2012
Thermodynamics of Finite Quantum Systems: Application to Spin Magnetism II
We extend our study of thermodynamics of a Kubo particle to temperatures
smaller than the interlevel spacing. We obtain the distribution functions of
spin susceptibility and heat capacity for Poisson and Wigner-Dyson level
statistics. We evaluate the line shape of the Knight shift due to spin effects
both in a single particle and for the ensemble average and compare it with
orbital and spin-orbit contributions.Comment: 20 pages (16 text, 4 figures) uu-encoded, z-compressed PostScript.
Latest versions of manuscripts available at
http://physuna.phs.uc.edu/professors/serota.html or by e-mail, by request
from [email protected]
Superconductor-proximity effect in chaotic and integrable billiards
We explore the effects of the proximity to a superconductor on the level
density of a billiard for the two extreme cases that the classical motion in
the billiard is chaotic or integrable. In zero magnetic field and for a uniform
phase in the superconductor, a chaotic billiard has an excitation gap equal to
the Thouless energy. In contrast, an integrable (rectangular or circular)
billiard has a reduced density of states near the Fermi level, but no gap. We
present numerical calculations for both cases in support of our analytical
results. For the chaotic case, we calculate how the gap closes as a function of
magnetic field or phase difference.Comment: 4 pages, RevTeX, 2 Encapsulated Postscript figures. To be published
by Physica Scripta in the proceedings of the "17th Nordic Semiconductor
Meeting", held in Trondheim, June 199
Evidence for the Validity of the Berry-Robnik Surmise in a Periodically Pulsed Spin System
We study the statistical properties of the spectrum of a quantum dynamical
system whose classical counterpart has a mixed phase space structure consisting
of two regular regions separated by a chaotical one. We make use of a simple
symmetry of the system to separate the eigenstates of the time-evolution
operator into two classes in agreement with the Percival classification scheme
\cite{Per}. We then use a method firstly developed by Bohigas et. al.
\cite{BoUlTo} to evaluate the fractional measure of states belonging to the
regular class, and finally present the level spacings statistics for each class
which confirm the validity of the Berry-Robnik surmise in our model.Comment: 15 pages, 9 figures available upon request, Latex fil
On the Accuracy of the Semiclassical Trace Formula
The semiclassical trace formula provides the basic construction from which
one derives the semiclassical approximation for the spectrum of quantum systems
which are chaotic in the classical limit. When the dimensionality of the system
increases, the mean level spacing decreases as , while the
semiclassical approximation is commonly believed to provide an accuracy of
order , independently of d. If this were true, the semiclassical trace
formula would be limited to systems in d <= 2 only. In the present work we set
about to define proper measures of the semiclassical spectral accuracy, and to
propose theoretical and numerical evidence to the effect that the semiclassical
accuracy, measured in units of the mean level spacing, depends only weakly (if
at all) on the dimensionality. Detailed and thorough numerical tests were
performed for the Sinai billiard in 2 and 3 dimensions, substantiating the
theoretical arguments.Comment: LaTeX, 31 pages, 14 figures, final version (minor changes
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