8,503 research outputs found
Squark-mediated Higgs+jets production at the LHC
We investigate possible scenarios of light-squark production at the LHC as a
new mechanism to produce Higgs bosons in association with jets. The study is
motivated by the SUSY search for H+jets events, performed by the CMS
collaboration on 8 and 13 TeV data using the razor variables. Two simplified
models are proposed to interpret the observations in this search. The
constraint from Run I and the implications for Run II and beyond are discussed
The tilt of the Fundamental Plane of Early-type galaxies: wavelength dependence
The photometric parameters R_e and mu_e of 74 early-type (E+S0+S0a) galaxies
in the Coma cluster are derived for the first time in the near IR H band. These
are used, coupled with measurements of the central velocity dispersion found in
the literature, to determine the H band Fundamental Plane (FP) relation of this
cluster. The same procedure is applied to previously available photometric data
in the B, V, r, I, and K bands, to perform a multi-wavelength study of the FP.
Because systematic uncertainties in the value of the FP parameters are
introduced both by the choice of the fitting algorithm, and by the presence of
statistical biases connected with the sample selection procedure, we emphasize
the importance of deriving the FP parameters in the six photometric bands using
an identical fitting algorithm, and appropriate corrections to eliminate the
effects of sample incompleteness. We find that the FP mu_e coefficient is
stable with wavelength, while the sigma coefficient increases significantly
with increasing wavelength, in agreement with an earlier result presented by
Pahre & Djorgovski. The slope of the FP relation, although changing with
wavelength, never approaches the virial theorem expectation. We also find that
the magnitude of the slope change can be entirely explained by the presence of
the well known relation between color and magnitude among early-type galaxies.
We conclude that the tilt of the Fundamental Plane is significant, and must be
due to some form of broken homology among early-type galaxies, while its
wavelength dependence derives from whatever mechanism (currently the preferred
one is the existence of a mass-metal content sequence) produces the
color-magnitude relation in those galaxies.Comment: 8 pages, 7 figures, 6 tables; table 3 should be printed in landscape
mode, and inserted into the text. Accepted for publication in MNRA
The nature of the red disk-like galaxies at high redshift: dust attenuation and intrinsically red stellar populations
We investigate which conditions of dust attenuation and stellar populations
allow models of dusty, continuously star-forming, bulge-less disk galaxies at
0.8<z<3.2 to meet the different colour selection criteria of high-z ``red''
galaxies (e.g. Rc-K>5.3, Ic-K>4, J-K>2.3). As a main novelty, we use stellar
population models that include the thermally pulsating Asymptotic Giant Branch
(TP-AGB) phase of stellar evolution. The star formation rate of the models
declines exponentially as a function of time, the e-folding time being longer
than 3 Gyr. In addition, we use calculations of radiative transfer of the
stellar and scattered radiation through different dusty interstellar media in
order to explore the wide parameter space of dust attenuation. We find that
synthetic disks can exhibit red optical/near-infrared colours because of
reddening by dust, but only if they have been forming stars for at least about
1 Gyr. Extremely few models barely exhibit Rc-K>5.3, if the inclination i=90
deg and if the opacity 2*tauV>6. Hence, Rc-K-selected galaxies at 1<z<2 most
probably are either systems with an old, passively evolving bulge or
starbursts. Synthetic disks at 1<z<2 exhibit 4<Ic-K<4.8, if they are seen edge
on (i.e. at i about 90 deg) and if 2*tauV>0.5. This explains the large fraction
of observed, edge-on disk-like galaxies with Ks4. Finally,
models with 2<z<3.2 exhibit 2.3<J-K<3, with no bias towards i about 90 deg and
for a large range in opacity (e.g. 2*tauV>1 for i about 70 deg). In conclusion,
red disk-like galaxies at 0.8<z<3.2 may not necessarily be dustier than nearby
disk galaxies (with 0.5<2*tauV<2) and/or much older than about 1 Gyr. This
result is due both to a realistic description of dust attenuation and to the
emission contribution by TP-AGB stars... (Abridged)Comment: 16 pages, 8 ps figures, accepted for publication in MNRA
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Measuring the impact of observations on the predictability of the Kuroshio Extension in a shallow-water model
In this paper sequential importance sampling is used to assess the impact of observations on a ensemble prediction for the decadal path transitions of the Kuroshio Extension (KE). This particle ïŹltering approach gives access to the probability density of the state vector, which allows us to determine the predictive power â an entropy based measure â of the ensemble prediction. The proposed set-up makes use of an ensemble that, at each time, samples the climatological probability distribution. Then, in a post-processing step, the impact of diïŹerent sets of observations is measured by the increase in predictive power of the ensemble over the climatological signal during one-year. The method is applied in an identical-twin
experiment for the Kuroshio Extension using a reduced-gravity shallow water model. We investigate the impact of assimilating velocity observations from diïŹerent locations during the elongated and the contracted meandering state of the KE. Optimal observations location correspond to regions with strong potential vorticity gradients. For the elongated state the optimal location is in the ïŹrst meander of the KE. During the contracted state of the KE it is located south of Japan, where the Kuroshio separates from the coast
Two-body nonleptonic B decays in the Standard Model and beyond
We briefly discuss the phenomenology of B to pi pi, B to K pi and B to phi K
decays in the Standard Model and in Supersymmetry.Comment: 7 pages, 2 figures, uses moriond.sty. Talk given by L. Silvestrini at
the XXXIXth Rencontres de Moriond on ElectroWeak Interactions and Unified
Theories, La Thuile, Aosta Valley, Italy, March 21st-28th 200
Higgs look-alikes at the LHC
The discovery of a Higgs particle is possible in a variety of search channels
at the LHC. However the true identity of any putative Higgs boson will at first
remain ambiguous, until one has experimentally excluded other possible
assignments of quantum numbers and couplings. We quantify to what degree one
can discriminate a Standard Model Higgs boson from "look-alikes" at, or close
to, the moment of discovery at the LHC. We focus on the fully-reconstructible
"golden" decay mode to a pair of Z bosons and a four-lepton final state,
simulating sPlot-weighted samples of signal and background events. Considering
both on-shell and off-shell Z's, we show how to utilize the full decay
information from the events, including the distributions and correlations of
the five relevant angular variables. We demonstrate how the finite phase space
acceptance of any LHC detector sculpts the decay distributions, a feature
neglected in previous studies. We use likelihood ratios to discriminate a
Standard Model Higgs from look-alikes with other spins or nonstandard parity,
CP, or form factors. For a benchmark resonance mass of 200 GeV/c^2, we achieve
a median expected discrimination significance of 3 sigma with as few as 19
events, and even better discrimination for the off-shell decays of a 145
GeV/c^2 resonance.Comment: 39 pages, 55 figures, typos fixed, figures added, and minor
clarification
1.65 micrometers (H-band) surface photometry of galaxies. III: observations of 558 galaxies with the TIRGO 1.5m telescope
We present near-infrared H-band (1.65 micron) surface photometry of 558
galaxies in the Coma Supercluster and in the Virgo cluster. This data set,
obtained with the Arcetri NICMOS3 camera ARNICA mounted on the Gornergrat
Infrared Telescope, is aimed at complementing, with observations of mostly
early-type objects, our NIR survey of spiral galaxies in these regions,
presented in previous papers of this series. Magnitudes at the optical radius,
total magnitudes, isophotal radii and light concentration indices are derived.
We confirm the existence of a positive correlation between the near-infrared
concentration index and the galaxy H-band luminosity. (Tables 1 and 2 are only
available in electronic form upon request to [email protected])Comment: 12 pages, 6 figures. Accepted for publication in A&A
Dust Attenuation in Late-Type Galaxies. I. Effects on Bulge and Disk Components
We present results of new Monte Carlo calculations made with the DIRTY code
of radiative transfer of stellar and scattered radiation for a dusty giant
late-type galaxy like the Milky Way, which illustrate the effect of the
attenuation of stellar light by internal dust on the integrated photometry of
the individual bulge and disk components. Here we focus on the behavior of the
attenuation function, the color excess, and the fraction of light scattered or
directly transmitted towards the outside observer as a function of the total
amount of dust and the inclination of the galaxy, and the structure of the
dusty interstellar medium (ISM) of the disk. We confirm that dust attenuation
produces qualitatively and quantitatively different effects on the integrated
photometry of bulge and disk, whatever the wavelength. In addition, we find
that the structure of the dusty ISM affects more sensitively the observed
magnitudes than the observed colors of both bulge and disk. Finally, we show
that the contribution of the scattered radiation to the total monochromatic
light received by the outside observer is significant, particularly at UV
wavelengths, even for a two-phase, clumpy, dusty ISM. Thus understanding dust
scattering properties is fundamental for the interpretation of extragalactic
observations in the rest-frame UV.Comment: 62 pages, 28 eps-figures, 1 table, accepted for publication in ApJ
Main Journa
Investigating The Physics Case of Running a B-Factory at the Y(5S) Resonance
We discuss the physics case of a high luminosity B-Factory running at the
Y(5S) resonance. We show that the coherence of the B meson pairs is preserved
at this resonance, and that Bs can be well distinguished from Bd and charged B
mesons. These facts allow to cover the physics program of a traditional
B-Factory and, at the same time, to perform complementary measurements which
are not accessible at the Y(4S). In particular we show how, despite the
experimental limitations in performing time-dependent measurements of Bs
decays, the same experimental information can be extracted, in several cases,
from the determination of time-integrated observables. In addition, a few
examples of the potentiality in measuring rare Bs decays are given. Finally, we
discuss how the study of Bs meson will improve the constraints on New Physics
parameters in the Bs sector, in the context of the generalized Unitarity
Triangle analysis.Comment: 47 pages, 22 figure
Aggiornamenti e novitĂ sulla distribuzione del genere Gagea (Liliaceae) in Toscana
Viene confermata la presenza di Gagea bohemica (zauschn.) Scuhlt. & Schult. f. nellâunica localitĂ nota per la Toscana (isola dâElba) e di G. granatellii (Parl.) Parl. allâisola del Giglio, dove da oltre 100 anni la specie non era stata piĂč osservata. Vengono anche segnalate nuove localitĂ di G. granatellii nella porzione centrale e orientale dellâisola dâElba, nonchĂ© di G. lutea (L.) Ker-Gawl. e di G. pratensis (Pers.) Dumort. nella Toscana settentrionale (Pracchie di Pontito e Monte Morello, rispettivamente)
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