76,492 research outputs found
Quasi-Periodic Oscillations and energy spectra from the two brightest Ultra-Luminous X-ray sources in M82
Ultra-Luminous X-ray sources are thought to be accreting black holes that
might host Intermediate Mass Black Holes (IMBH), proposed to exist by
theoretical studies, even though a firm detection (as a class) is still
missing. The brightest ULX in M82 (M82 X-1) is probably one of the best
candidates to host an IMBH. In this work we analyzed the data of the recent
release of observations obtained from M82 X-1 taken by XMM-Newton. We performed
a study of the timing and spectral properties of the source. We report on the
detection of (46+-2) mHz Quasi-Periodic Oscillations (QPOs) in the power
density spectra of two observations. A comparison of the frequency of these
high-frequency QPOs with previous detections supports the 1:2:3 frequency
distribution as suggested in other studies. We discuss the implications if the
(46+-2) mHz QPO detected in M82 X-1 is the fundamental harmonic, in analogy
with the High-Frequency QPOs observed in black hole binaries. For one of the
observations we have detected for the first time a QPO at 8 mHz (albeit at a
low significance), that coincides with a hardening of the spectrum. We suggest
that the QPO is a milli-hertz QPO originating from the close-by transient ULX
M82 X-2, with analogies to the Low-Frequency QPOs observed in black hole
binaries.Comment: 9 pages (with 4 figures and 4 tables). Accepted for publication in
MNRAS (26/09/13
Quantum computational tensor network on string-net condensate
The string-net condensate is a new class of materials which exhibits the
quantum topological order. In order to answer the important question, "how
useful is the string-net condensate in quantum information processing?", we
consider the most basic example of the string-net condensate, namely the
gauge string-net condensate on the two-dimensional hexagonal lattice, and show
that the universal measurement-based quantum computation (in the sense of the
quantum computational webs) is possible on it by using the framework of the
quantum computational tensor network. This result implies that even the most
basic example of the string-net condensate is equipped with the correlation
space that has the capacity for the universal quantum computation.Comment: 5 pages, 4 figure
Non-analyticities in three-dimensional gauge theories
Quantum fluctuations generate in three-dimensional gauge theories not only
radiative corrections to the Chern-Simons coupling but also non-analytic terms
in the effective action. We review the role of those terms in gauge theories
with massless fermions and Chern-Simons theories. The explicit form of
non-analytic terms turns out to be dependent on the regularization scheme and
in consequence the very existence of phenomena like parity and framing
anomalies becomes regularization dependent. In particular we find
regularization regimes where both anomalies are absent. Due to the presence of
non-analytic terms the effective action becomes not only discontinuous but also
singular for some background gauge fields which include sphalerons. The
appearence of this type of singularities is linked to the existence of nodal
configurations in physical states and tunneling suppression at some classical
field configurations. In the topological field theory the number of physical
states may also become regularization dependent. Another consequence of the
peculiar behaviour of three-dimensional theories under parity odd
regularizations is the existence of a simple mechanism of generation of a mass
gap in pure Yang-Mills theory by a suitable choice of regularization scheme.
The generic value of this mass does agree with the values obtained in
Hamiltonian and numerical analysis. Finally, the existence of different
regularization regimes unveils the difficulties of establishing a Zamolodchikov
c-theorem for three-dimensional field theories in terms of the induced
gravitational Chern-Simons couplings.Comment: 21 pages; Contribution to Ian Kogan Memorial Collection, ``From
Fields to Strings: Circumnavigating Theoretical Physics'
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A new Lyropecten (Pectinidae, Bivalvia, Mollusca) from the central California Miocene, USA
A new pectinid, Lyropecten terrysmithae n. sp., has been recognized in middle to late Miocene rock units referred to as the Monterey Formation and Santa Margarita Sandstone in the southern Salinas Valley, central California. Previously, L. terrysmithae had been identified as a flat form belonging to either L. estrellanus or L. catalinae, then more recently to Argopecten sp. The earlier assignments were based on its moderate size and a radial rib count nearly identical to these taxa. However, its hinge, flat unledged valves, looped lamellar growth lines, and hinge crura set L. terrysmithae apart from Argopecten and all species of Lyropecten. Localities where it occurs in the Salinas Valley that can be accurately dated are from the late middle to middle late Miocene “Margaritan” California provincial molluscan stage. While L. terrysmithae has been collected at other sites, those localities lack diagnostic age-specific species necessary to determine an accurate geological age and maybe older
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