525 research outputs found
Two-loop electroweak top corrections: are they under control?
The assumption that two-loop top corrections are well approximated by the
contribution is investigated. It is shown that in the case of
the ratio neutral-to-charged current amplitudes at zero momentum transfer the
terms are numerically comparable to the
contribution for realistic values of the top mass. An estimate of the
theoretical error due to unknown two-loop top effect is presented for a few
observables of LEP interest.Comment: 13 pages, LaTeX using equations, doublespace, cite macros. Hard
copies of the paper including one figure are available from
[email protected]
Fermion Virtual Effects in Cross Section
We analyse the contribution of new heavy virtual fermions to the cross section. We find that there exists a relevant
interplay between trilinear and bilinear oblique corrections. The result
strongly depends on the chiral or vector--like nature of the new fermions. As
for the chiral case we consider sequential fermions: one obtains substantial
deviation from the Standard model prediction, making the effect possibly
detectable at or GeV linear colliders. As an example for
the vector--like case we take a SUSY extension with heavy charginos and
neutralinos: due to cancellation, the final effect turns out to be negligible.Comment: uuencoded, gz-compressed, tar-ed file. 8 pages, 4 EPS figures, uses
EPSFIG.ST
Multiphase gas flows in the nearby Seyfert galaxy ESO428-G14
We present ALMA rest-frame 230 GHz continuum and CO(2-1) line observations of
the nearby Compton-thick Seyfert galaxy ESO428-G14, with angular resolution 0.7
arcsec (78 pc). We detect CO(2-1) emission from spiral arms and a
circum-nuclear ring with 200 pc radius, and from a transverse gas lane with
size of pc, which crosses the nucleus and connects the two portions
the circumnuclear ring. The molecular gas in the host galaxy is distributed in
a rotating disk with intrinsic circular velocity km/s,
inclination deg, and dynamical mass within a radius of kpc. In the inner 100 pc region CO is
distributed in a equatorial bar, whose kinematics is highly perturbed and
consistent with an inflow of gas towards the AGN. This inner CO bar overlaps
with the most obscured, Compton-thick region seen in X-rays. We derive a column
density of in this region,
suggesting that molecular gas may contribute significantly to the AGN
obscuration. We detect a molecular outflow with a total outflow rate , distributed along a bi-conical structure with
size of pc on both sides of the AGN. The bi-conical outflow is also
detected in the emission line at 2.12 m, which traces a warmer
nuclear outflow located within 170 pc from the AGN. This suggests that the
outflow cools with increasing distance from the AGN. We find that the hard
X-ray emitting nuclear region mapped with Chandra is CO-deprived, but filled
with warm molecular gas traced by - thus confirming that the hard
(3-6 keV) continuum and Fe K emission are due to scattering from dense
neutral clouds in the ISM.Comment: Submitted to Ap
Effective Lagrangian for Heavy and Light Mesons: Semileptonic Decays
We introduce an effective lagrangian including negative and positive parity
heavy mesons containing a heavy quark, light pseudoscalars, and light vector
resonances, with their allowed interactions, using heavy quark spin-flavour
symmetry, chiral symmetry, and the hidden symmetry approach for light vector
resonances. On the basis of such a lagrangian, by considering the allowed weak
currents and by including the contributions from the nearest unitarity poles we
calculate the form factors for semileptonic decays of and mesons into
light pseudoscalars and light vector resonances. The available data, together
with some additional assumptions, allow for a set of predictions in the
different semileptonic channels, which can be compared with those following
{}from different approaches. A discussion of non-dominant terms in our
approach, which attempts at including a rather complete dynamics, will however
have to wait till more abundant data become available.Comment: LaTeX (style article), 19 pages, UGVA-DPT 1992/11-790, BARI-TH/92-12
AGN counts at 15um. XMM observations of the ELAIS-S1-5 sample
Context: The counts of galaxies and AGN in the mid infra-red (MIR) bands are
important instruments for studying their cosmological evolution. However, the
classic spectral line ratios techniques can become misleading when trying to
properly separate AGN from starbursts or even from apparently normal galaxies.
Aims: We use X-ray band observations to discriminate AGN activity in
previously classified MIR-selected starburst galaxies and to derive updated
AGN1 and (Compton thin) AGN2 counts at 15 um.
Methods: XMM observations of the ELAIS-S1 15um sample down to flux limits
~2x10^-15 erg cm^-2 s^-1 (2-10 keV band) were used. We classified as AGN all
those MIR sources with a unabsorbed 2-10 keV X-ray luminosity higher that
~10^42 erg/s.
Results: We find that at least about 13(+/-6) per cent of the previously
classified starburst galaxies harbor an AGN. According to these figures, we
provide an updated estimate of the counts of AGN1 and (Compton thin) AGN2 at 15
um. It turns out that at least 24% of the extragalactic sources brighter than
0.6 my at 15 um are AGN (~13% contribution to the extragalactic background
produced at fluxes brighter than 0.6 mJy).Comment: Accepted for publication on A&
The Golden Ratio Prediction for the Solar Angle from a Natural Model with A5 Flavour Symmetry
We formulate a consistent model predicting, in the leading order
approximation, maximal atmospheric mixing angle, vanishing reactor angle and
tan {\theta}_12 = 1/{\phi} where {\phi} is the Golden Ratio. The model is based
on the flavour symmetry A5 \times Z5 \times Z3, spontaneously broken by a set
of flavon fields. By minimizing the scalar potential of the theory up to the
next-to-leading order in the symmetry breaking parameter, we demonstrate that
this mixing pattern is naturally achieved in a finite portion of the parameter
space, through the vacuum alignment of the flavon fields. The leading order
approximation is stable against higher-order corrections. We also compare our
construction to other models based on discrete symmetry groups.Comment: 28 pages, 2 figures. Minor changes, references added. Corrected typos
in Appendix A. Version appeared on JHE
The rest-frame UV-to-optical spectroscopy of APM 08279+5255 - BAL classification and black hole mass estimates
We present the analysis of the rest-frame optical-to-UV spectrum of APM
08279+5255, a well-known lensed broad absorption line (BAL) quasar at . The spectroscopic data are taken with the optical DOLoRes and near-IR
NICS instruments at TNG, and include the previously unexplored range between C
III] 1910 and [O III] 4959,5007. We investigate the
possible presence of multiple BALs by computing "balnicity" and absorption
indexes (i.e. BI, BI and AI) for the transitions Si IV 1400, C IV
1549, Al III 1860 and Mg II 2800. No clear evidence
for the presence of absorption features is found in addition to the already
known, prominent BAL associated to C IV, which supports a high-ionization BAL
classification for APM 08279+5255. We also study the properties of the [O III],
H and Mg II emission lines. We find that [O III] is intrinsically weak
(), as it is typically found in
luminous quasars with a strongly blueshifted C IV emission line (2500 km
s for APM 08279+5255). We compute the single-epoch black hole mass based
on Mg II and H broad emission lines, finding M, with the magnification factor that can
vary between 4 and 100 according to CO and rest-frame UV-to-mid-IR imaging
respectively. Using a Mg II equivalent width (EW)-to-Eddington ratio relation,
the EW \AA\ measured for APM 08279+5255 translates into an
Eddington ratio of 0.4, which is more consistent with . This
magnification factor also provides a value of that is consistent
with recent reverberation-mapping measurements derived from C IV and Si IV.Comment: 10 pages, 4 figures, 4 tables, accepted for publication in A&
Blowin' in the wind: both `negative' and `positive' feedback in an obscured high-z Quasar
Quasar feedback in the form of powerful outflows is invoked as a key
mechanism to quench star formation in galaxies, preventing massive galaxies to
over-grow and producing the red colors of ellipticals. On the other hand, some
models are also requiring `positive' AGN feedback, inducing star formation in
the host galaxy through enhanced gas pressure in the interstellar medium.
However, finding observational evidence of the effects of both types of
feedback is still one of the main challenges of extragalactic astronomy, as few
observations of energetic and extended radiatively-driven winds are available.
Here we present SINFONI near infrared integral field spectroscopy of XID2028,
an obscured, radio-quiet z=1.59 QSO detected in the XMM-COSMOS survey, in which
we clearly resolve a fast (1500 km/s) and extended (up to 13 kpc from the black
hole) outflow in the [OIII] lines emitting gas, whose large velocity and
outflow rate are not sustainable by star formation only. The narrow component
of Ha emission and the rest frame U band flux from HST-ACS imaging enable to
map the current star formation in the host galaxy: both tracers independently
show that the outflow position lies in the center of an empty cavity surrounded
by star forming regions on its edge. The outflow is therefore removing the gas
from the host galaxy (`negative feedback'), but also triggering star formation
by outflow induced pressure at the edges (`positive feedback'). XID2028
represents the first example of a host galaxy showing both types of feedback
simultaneously at work.Comment: 9 pages, 5 figures, accepted for publication in Ap
Universal Constraints on Low-Energy Flavour Models
It is pointed out that in a general class of flavour models one can identify
certain universally present FCNC operators, induced by the exchange of heavy
flavour messengers. Their coefficients depend on the rotation angles that
connect flavour and fermion mass basis. The lower bounds on the messenger scale
are derived using updated experimental constraints on the FCNC operators. The
obtained bounds are different for different operators and in addition they
depend on the chosen set of rotations. Given the sensitivity expected in the
forthcoming experiments, the present analysis suggests interesting room for
discovering new physics. As the highlights emerge the leptonic processes,
, and
conversion in nuclei.Comment: 18 pages, 3 figures; v2 matches published versio
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