10,488 research outputs found
Regular R-R and NS-NS BPS black holes
We show in a precise group theoretical fashion how the generating solution of
regular BPS black holes of N=8 supergravity, which is known to be a solution
also of a simpler N=2 STU model truncation, can be characterized as NS-NS or
R-R charged according to the way the corresponding STU model is embedded in the
original N=8 theory. Of particular interest is the class of embeddings which
yield regular BPS black hole solutions carrying only R-R charge and whose
microscopic description can possibly be given in terms of bound states of
D-branes only. The microscopic interpretation of the bosonic fields in this
class of STU models relies on the solvable Lie algebra (SLA) method. In the
present article we improve this mathematical technique in order to provide two
distinct descriptions for type IIA and type IIB theories and an algebraic
characterization of S*T--dual embeddings within the N=8,d=4 theory. This
analysis will be applied to the particular example of a four parameter
(dilatonic) solution of which both the full macroscopic and microscopic
descriptions will be worked out.Comment: latex, 30 pages. Final version to appear on Int.J.Mod.Phy
Business surveys modelling with Seasonal-Cyclical Long Memory models.
Business surveys are an important element in the analysis of the short-term economic situation because of the timeliness and nature of the information they convey. Especially, surveys are often involved in econometric models in order to provide an early assessment of the current state of the economy, which is of great interest for policy-makers. In this paper, we focus on non-seasonally adjusted business surveys relative to the Euro area released by the European Commission. We introduce an innovative way for modelling those series taking the persistence of the seasonal roots into account through seasonal-cyclical long memory models. We empirically prove that such models produce more accurate forecasts than classical seasonal linear models.Euro area ; business surveys ; seasonal ; long memory.
The faintest galaxies
We investigate the nature of Ultra Faint dwarf spheroidal galaxies (UF dSphs)
in a general cosmological context, simultaneously accounting for various
"classical" dSphs and Milky Way (MW) properties, including their Metallicity
Distribution Function (MDF). The model successfully reproduces both the
observed [Fe/H]-Luminosity relation and the mean MDF of UFs. According to our
results UFs are the living fossils of H2-cooling minihaloes formed at z>8.5,
i.e. before the end of reionization. They are the oldest and the most dark
matter-dominated (M/L > 100) dSphs in the MW system, with a total mass of M =
10^(7-8) Msun. The model allows to interpret the different shape of UFs and
classical dSphs MDF, along with the frequency of extremely metal-poor stars in
these objects. We discuss the "missing satellites problem" by comparing the UF
star formation efficiencies with those derived for minihaloes in the Via Lactea
simulation.Comment: To appear in the conference proceeding: "First Stars and Galaxies:
Challenges in the Next Decade" . Publisher: American Institute of Physics.
Editors: V. Bromm, D. Whalen, N. Yoshid
Higher-spin current multiplets in operator-product expansions
Various formulas for currents with arbitrary spin are worked out in general
space-time dimension, in the free field limit and, at the bare level, in
presence of interactions. As the n-dimensional generalization of the
(conformal) vector field, the (n/2-1)-form is used. The two-point functions and
the higher-spin central charges are evaluated at one loop. As an application,
the higher-spin hierarchies generated by the stress-tensor operator-product
expansion are computed in supersymmetric theories. The results exhibit an
interesting universality.Comment: 19 pages. Introductory paragraph, misprint corrected and updated
references. CQG in pres
An Equivariant Tamagawa Number Formula for Drinfeld Modules and Applications
We fix data consisting of a Galois extension of
characteristic global fields with arbitrary abelian Galois group and a
Drinfeld module defined over a certain Dedekind subring of . For this
data, we define a -equivariant -function and prove an
equivariant Tamagawa number formula for certain Euler-completed versions of its
special value . This generalizes Taelman's class number
formula for the value of the Goss zeta function
associated to the pair . Taelman's result is obtained from our result
by setting . As a consequence, we prove a perfect Drinfeld module analogue
of the classical (number field) refined Brumer--Stark conjecture, relating a
certain -Fitting ideal of Taelman's class group to the special
value in question
Initial mass function of intermediate mass black hole seeds
We study the Initial Mass Function (IMF) and host halo properties of
Intermediate Mass Black Holes (IMBH, 10^{4-6} Msun) formed inside metal-free,
UV illuminated atomic cooling haloes (virial temperature T_vir > 10^4 K) either
via the direct collapse of the gas or via an intermediate Super Massive Star
(SMS) stage. We achieve this goal in three steps: (a) we derive the gas
accretion rate for a proto-SMS to undergo General Relativity instability and
produce a direct collapse black hole (DCBH) or to enter the ZAMS and later
collapse into a IMBH; (b) we use merger-tree simulations to select atomic
cooling halos in which either a DCBH or SMS can form and grow, accounting for
metal enrichment and major mergers that halt the growth of the proto-SMS by gas
fragmentation. We derive the properties of the host halos and the mass
distribution of black holes at this stage, and dub it the "Birth Mass
Function"; (c) we follow the further growth of the DCBH due to accretion of
leftover gas in the parent halo and compute the final IMBH mass.We consider two
extreme cases in which minihalos (T_vir < 10^4 K) can (fertile) or cannot
(sterile) form stars and pollute their gas leading to a different IMBH IMF. In
the (fiducial) fertile case the IMF is bimodal extending over a broad range of
masses, M= (0.5-20)x10^5 Msun, and the DCBH accretion phase lasts from 10 to
100 Myr. If minihalos are sterile, the IMF spans the narrower mass range M=
(1-2.8)x10^6 Msun, and the DCBH accretion phase is more extended (70-120 Myr).
We conclude that a good seeding prescription is to populate halos (a) of mass
7.5 < log (M_h/Msun) < 8, (b) in the redshift range 8 < z < 17, (c) with IMBH
in the mass range 4.75 < log (M_BH/Msun) < 6.25.Comment: MNRAS, in press. Comments welcom
Finite-Size Effects and Operator Product Expansions in a CFT for d>2
The large momentum expansion for the inverse propagator of the auxiliary
field in the conformally invariant O(N) vector model is calculated
to leading order in 1/N, in a strip-like geometry with one finite dimension of
length for . Its leading terms are identified as contributions from
itself and the energy momentum tensor, in agreement with a
previous calculation based on conformal operator product expansions. It is
found that a non-trivial cancellation takes place by virtue of the gap
equation. The leading coefficient of the energy momentum tensor contribution is
shown to be related to the free energy density.Comment: 10 pages LaTeX 2 eps figures, minor changes in text. Revised version
to be published in Phys.Lett. B. email: [email protected]
[email protected]
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