8,912 research outputs found
On Arnold's 14 `exceptional' N=2 superconformal gauge theories
We study the four-dimensional superconformal N=2 gauge theories engineered by
the Type IIB superstring on Arnold's 14 exceptional unimodal singularities
(a.k.a. Arnold's strange duality list), thus extending the methods of 1006.3435
to singularities which are not the direct sum of minimal ones. In particular,
we compute their BPS spectra in several `strongly coupled' chambers.
From the TBA side, we construct ten new periodic Y-systems, providing
additional evidence for the existence of a periodic Y-system for each isolated
quasi-homogeneous singularity with (more generally, for each N=2
superconformal theory with a finite BPS chamber whose chiral primaries have
dimensions of the form N/l).Comment: 73 pages, 7 figure
Potts q-color field theory and scaling random cluster model
We study structural properties of the q-color Potts field theory which, for
real values of q, describes the scaling limit of the random cluster model. We
show that the number of independent n-point Potts spin correlators coincides
with that of independent n-point cluster connectivities and is given by
generalized Bell numbers. Only a subset of these spin correlators enters the
determination of the Potts magnetic properties for q integer. The structure of
the operator product expansion of the spin fields for generic q is also
identified. For the two-dimensional case, we analyze the duality relation
between spin and kink field correlators, both for the bulk and boundary cases,
obtaining in particular a sum rule for the kink-kink elastic scattering
amplitudes.Comment: 27 pages; 6 figures. Published version, some comments and references
adde
Quantum gauge symmetries in Noncommutative Geometry
We discuss generalizations of the notion of i) the group of unitary elements
of a (real or complex) finite dimensional C*-algebra, ii) gauge transformations
and iii) (real) automorphisms, in the framework of compact quantum group theory
and spectral triples. The quantum analogue of these groups are defined as
universal (initial) objects in some natural categories. After proving the
existence of the universal objects, we discuss several examples that are of
interest to physics, as they appear in the noncommutative geometry approach to
particle physics: in particular, the C*-algebras M_n(R), M_n(C) and M_n(H),
describing the finite noncommutative space of the Einstein-Yang-Mills systems,
and the algebras A_F=C+H+M_3(C) and A^{ev}=H+H+M_4(C), that appear in
Chamseddine-Connes derivation of the Standard Model of particle physics
minimally coupled to gravity. As a byproduct, we identify a "free" version of
the symplectic group Sp(n) (quaternionic unitary group).Comment: 31 pages, no figures; v2: minor changes, added reference
On the generation of sequential unitary gates from continuous time Schrodinger equations driven by external fields
In all the various proposals for quantum computers, a common feature is that
the quantum circuits are expected to be made of cascades of unitary
transformations acting on the quantum states. A framework is proposed to
express these elementary quantum gates directly in terms of the control inputs
entering into the continuous time forced Schrodinger equation.Comment: 10 page
Understanding the nature of FRII optical nuclei: a new diagnostic plane for radio galaxies
We extend our study of the nuclei of 3CR FR II radio galaxies through HST
optical images up to z=0.3. In the majority of them an unresolved nucleus
(central compact core, CCC) is found. We analyze their position in the plane
formed by the radio and optical nuclear luminosities in relation to their
optical spectral properties. The broad-lined objects (BLO) have the brightest
nuclei: they are present only at optical luminosities nu L_nu > 4 X 10^42 erg
s^-1 which we suggest might represent a threshold in the radiative efficiency
combined to a small range of black hole masses. About 40 % of the high and low
excitation galaxies (HEG and LEG) show CCC which resemble those previously
detected in FR I galaxies, in apparent contrast to the unification model. The
equivalent width of the [OIII] emission line (with respect to the nuclear
luminosity) reveals the nature of these nuclei, indicating that the nuclei of
HEG are obscured to our line of sight and only scattered radiation is observed.
This implies that the population of FR II is composed by objects with different
nuclear properties, and only a fraction of them can be unified with quasars.Comment: 11 pages, 6 figures, in press on Astronomy & Astrophysics, minor
changes have been mad
Trade-off between angular resolution and straylight contamination in CMB anisotropy experiments. II. Straylight evaluation
Satellite CMB anisotropy missions and new generation of balloon-borne and
ground experiments, make use of complex multi-frequency instruments at the
focus of a meter class telescope. Between 70 GHz and 300 GHz, where foreground
contamination is minimum, it is extremely important to reach the best trade-off
between the improvement of the angular resolution and the minimization of the
straylight contamination mainly due to the Galactic emission. We focus here, as
a working case, on the 30 and 100 GHz channels of the Planck Low Frequency
Instrument (LFI). We evaluate the GSC introduced by the most relevant Galactic
foreground components for a reference set of optical configurations. We show
that it is possible to improve the angular resolution of 5-7% by keeping the
overall GSC below the level of few microKelvin. A comparison between the level
of straylight introduced by the different Galactic components for different
beam regions is presented. Simple approximate relations giving the rms and
peak-to-peak levels of the GSC are provided. We compare the results obtained at
100 GHz with those at 30 GHz, where GSC is more critical. Finally, we compare
the results based on Galactic foreground templates derived from radio and IR
surveys with those based on WMAP maps including CMB and extragalactic source
fluctuations.Comment: Submitted to A&A. Quality of the figures was degraded for
size-related reason
High Frequency Peakers: young radio sources or flaring blazars?
We present new, simultaneous, multifrequency observations of 45 out of the 55
candidate High Frequency Peakers (HFP) selected by Dallacasa et al. (2000),
carried out 3 to 4 years after a first set of observations. Our sub-sample
consists of 10 galaxies, 28 stellar objects (``quasars'') and 7 unidentified
sources. Both sets of observations are sensitive enough to allow the detection
of variability at the 10% level or lower. While galaxies do not show
significant variability, most quasars do. Seven of them no longer show the
convex spectrum which is the defining property of Gigahertz Peaked Spectrum
(GPS)/HFP sources and are interpreted as blazars caught by Dallacasa et al.
(2000) during a flare, when a highly self-absorbed component dominated the
emission. In general, the variability properties (amplitude, timescales,
correlation between peak luminosity and peak frequency of the flaring
component) of the quasar sub-sample resemble those of blazars. We thus conclude
that most HFP candidates identified with quasars may well be flaring blazars.Comment: 20 pages, 18 figures, accepted for publication in Astronomy &
Astrophysic
Probing the nuclear obscuration in radio-galaxies with near infrared imaging
We present the first near-infrared (K'-band) homogeneous observations of a
complete sub-sample of the 3CR radio catalogue comprising all High Excitation
Galaxies (HEGs) at z<0.3. After showing that the surface brightness
decomposition technique to measure central point-like sources is affected by
significant uncertainties for the objects in the studied sample, we present a
new, more accurate method based on the R-K' color profile. Via this method we
find a substantial nuclear K'-band excess in all but two HEGs -- most likely
directly associated to their nuclear emission -- and we measure the
corresponding 2.12 m nuclear luminosities. Within the frame of the
unification scheme for radio-loud active galactic nuclei, it appears that
obscuration alone is not able to account for the different nuclear properties
of the majority of the HEGs and Broad Line Radio Galaxies (BLRGs), and also
scattering of the (optically) hidden nuclear light from a compact region must
be invoked. More precisely, for ~70% of the HEGs the observed point-like
optical emission is dominated by the scattered component, while in the K'-band
both scattered and direct light passing through the torus contribute to the
observed nuclear luminosity. The estimated fraction of scattered light ranges
from a few tenths to a few percent, while the torus extinction is between
15<A_{V,torus}<50 mag with only a few exceptions with lower obscuration.Comment: Accepted for publication in A&A; high resolution version can be
downloaded at http://www.astro.yale.edu/danilom
The Universal Rotation Curve of Spiral Galaxies. II The Dark Matter Distribution out to the Virial Radius
In the current LambdaCDM cosmological scenario, N-body simulations provide us
with a Universal mass profile, and consequently a Universal equilibrium
circular velocity of the virialized objects, as galaxies. In this paper we
obtain, by combining kinematical data of their inner regions with global
observational properties, the Universal Rotation Curve (URC) of disk galaxies
and the corresponding mass distribution out to their virial radius. This curve
extends the results of Paper I, concerning the inner luminous regions of Sb-Im
spirals, out to the edge of the galaxy halos.Comment: In press on MNRAS. 10 pages, 8 figures. The Mathematica code for the
figures is available at: http://www.novicosmo.org/salucci.asp Corrected typo
Primordial black hole formation in the early universe: critical behaviour and self-similarity
Following on after three previous papers discussing the formation of
primordial black holes during the radiative era of the early universe, we
present here a further investigation of the critical nature of the process
involved, aimed at making contact with some of the basic underlying ideas from
the literature on critical collapse. We focus on the intermediate state, which
we have found appearing in cases with perturbations close to the critical
limit, and examine the connection between this and the similarity solutions
which play a fundamental role in the standard picture of critical collapse. We
have derived a set of self-similar equations for the null-slicing form of the
metric which we are using for our numerical calculations, and have then
compared the results obtained by integrating these with the ones coming from
our simulations for collapse of cosmological perturbations within an expanding
universe. We find that the similarity solution is asymptotically approached in
a region which grows to cover both the contracting matter and part of the
semi-void which forms outside it. Our main interest is in the situation
relevant for primordial black hole formation in the radiative era of the early
universe, where the relation between the pressure and the energy density
can be reasonably approximated by an expression of the form with
. However, we have also looked at other values of , both because
these have been considered in previous literature and also because they can be
helpful for giving further insight into situations relevant for primordial
black hole formation. As in our previous work, we have started our simulations
with initial supra-horizon scale perturbations of a type which could have come
from inflation.Comment: 23 pages, 8 figures, new abstract, submitted to Classical and Quantum
Gravity. This new version of the paper has been completely rewritten with
respect the previous one, with several changes and substantial additional
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