1,050 research outputs found
Heavy-heavy form factors and generalized factorization
We reanalyze B -> D pi and B -> K J/psi data to extract a set of parameters
which give the relevant hadronic matrix elements in terms of factorized
amplitudes. Various sources of theoretical uncertainties are studied, in
particular those depending on the model adopted for the form factors. We find
that the fit to the B -> D pi branching ratios substantially depends on the
model describing the Isgur-Wise function and on the value of its slope. This
dependence can be reduced by substituting the BR(B -> D pi) with suitable
ratios of non-leptonic to differential semileptonic BRs. In this way, we obtain
a model-independent determination of these parameters. Using these results, the
B -> D form factors at q^2=M_pi^2 can be extracted from a fit of the BR(B -> D
pi). The comparison between the form factors obtained in this way and the
corresponding measurements in semileptonic decays can be used as a test of
(generalized) factorization free from the uncertainties due to heavy-heavy form
factor modeling. Finally, we present predictions for yet-unmeasured D pi and D
K branching ratios and extract f_{D_s} and f_{D_s^*} from B -> DD_s decays. We
find f_{D_s} = 270 +- 45 MeV and f_{D_s^*}=260 +- 40 MeV, in good agreement
with recent measurements and lattice calculations.Comment: 20 pages, 16 ps/eps files, uses epsfig.sty; exp. numbers update
Partly Supersymmetric Grand Unification
It is shown how grand unification can occur in models which are partly
supersymmetric. The particle states which are composite do not contribute to
the running of gauge couplings above the compositeness scale, while the
elementary states contribute the usual large logarithmns. This introduces a new
differential running contribution to the gauge couplings from partly composite
SU(5) matter multiplets. In particular, for partly supersymmetric models, the
incomplete SU(5) elementary matter multiplets restore gauge coupling
unification even though the usual elementary gaugino and Higgsino contributions
need not be present.Comment: 14 pages, LaTe
Factorization, charming penguins, and all that
We discuss few selected topics related to the calculation of hadronic
amplitudes relevant for two-body non-leptonic B decays.Comment: LaTeX, 9 pages, 1 eps figure included, uses psfig.sty. Talk given by
M.C. at Beauty '97, UCLA, USA, October 13-17, 199
Discovering the composite Higgs through the decay of a heavy fermion
A possible composite nature of the Higgs could be revealed at the early stage
of the LHC, by analyzing the channels where the Higgs is produced from the
decay of a heavy fermion. The Higgs production from a singly-produced heavy
bottom, in particular, proves to be a promising channel. For a value \lambda=3
of the Higgs coupling to a heavy bottom, for example, we find that, considering
a 125 GeV Higgs which decays into a pair of b-quarks, a discovery is possible
at the 8 TeV LHC with 30 fb^{-1} if the heavy bottom is lighter than roughly
530 GeV (while an observation is possible for heavy bottom masses up to 650
GeV). Such a relatively light heavy bottom is realistic in composite Higgs
models of the type considered and, up to now, experimentally allowed. At
\sqrt{s}=14 TeV the LHC sensitivity on the channel increases significantly.
With \lambda=3 a discovery can occur, with 100 fb^{-1}, for heavy bottom masses
up to 1040 GeV. In the case the heavy bottom was as light as 500 GeV, the 14
TeV LHC would be sensitive to the measure of the \lambda\ coupling in basically
the full range \lambda>1 predicted by the theory.Comment: 25 pp. v2: Minor changes. v3: Version accepted for publication in
JHEP. v4: typos fixe
Holography for fermions
The holographic interpretation is a useful tool to describe 5D field theories
in a 4D language. In particular it allows one to relate 5D AdS theories with 4D
CFTs. We elaborate on the 5D/4D dictionary for the case of fermions in AdS
with boundaries. This dictionary is quite useful to address phenomenological
issues in a very simple manner, as we show by giving some examples.Comment: 22 pages, 2 figures; v2: minor corrections, references adde
The Other Natural Two Higgs Doublet Model
We characterize models where electroweak symmetry breaking is driven by two
light Higgs doublets arising as pseudo-Nambu-Goldstone bosons of new dynamics
above the weak scale. They represent the simplest natural two Higgs doublet
alternative to supersymmetry. We construct their low-energy effective
Lagrangian making only few specific assumptions about the strong sector. These
concern their global symmetries, their patterns of spontaneous breaking and the
sources of explicit breaking. In particular we assume that all the explicit
breaking is associated with the couplings of the strong sector to the Standard
Model fields, that is gauge and (proto)-Yukawa interactions. Under those
assumptions the scalar potential is determined at lowest order by very few free
parameters associated to the top sector. Another crucial property of our
scenarios is the presence of a discrete symmetry, in addition to custodial
SO(4), that controls the -parameter. That can either be simple CP or a
that distinguishes the two Higgs doublets. Among various possibilities we study
in detail models based on SO(6)/SO(4) SO(2), focussing on their
predictions for the structure of the scalar spectrum and the deviations of
their couplings from those of a generic renormalizable two Higgs doublet model.Comment: 54 page
Strain rate, temperature and deformation state effect on Ecoflex 00-50 silicone mechanical behaviour
Silicone elastomers are extremely attractive materials due to their wide range of possible applications, from biomedical engineering to soft robotics. In this work, an extensive thermo-mechanical characterization of Ecoflex Shore hardness 00â50, a commercially available silicone elastomer, has been carried out to compensate for the lack of relevant literature. The mechanical behaviour of the material has been characterized by performing monotonic and cyclic loading tests. These tests were performed in different deformation states, i.e. uniaxial tension, pure shear and biaxial tension, at different strain rates and temperatures. Experimental findings allowed to highlight the material time-dependent response and quantify the contribution of dissipative deformation phenomena to the overall strain energy. Uniaxial tensile tests performed at different temperatures (between â40 °C and 140 °C) showed that the material mechanical behaviour is sensitive to temperature in this range: a decrease of the ultimate stress and strain has been observed with increasing temperature. Finally, the data obtained from the latter tests have been used to define a failure envelope, applied for the first time to Ecoflex silicones, and valuable to describe the material ultimate stress and strain at any temperature and strain rate
Partially Supersymmetric Composite Higgs Models
We study the idea of the Higgs as a pseudo-Goldstone boson within the
framework of partial supersymmetry in Randall-Sundrum scenarios and their CFT
duals. The Higgs and third generation of the MSSM are composites arising from a
strongly coupled supersymmetric CFT with global symmetry SO(5) spontaneously
broken to SO(4), whilst the light generations and gauge fields are elementary
degrees of freedom whose couplings to the strong sector explicitly break the
global symmetry as well as supersymmetry. The presence of supersymmetry in the
strong sector may allow the compositeness scale to be raised to ~10 TeV without
fine tuning, consistent with the bounds from precision electro-weak
measurements and flavour physics. The supersymmetric flavour problem is also
solved. At low energies, this scenario reduces to the "More Minimal
Supersymmetric Standard Model" where only stops, Higgsinos and gauginos are
light and within reach of the LHC.Comment: 28 pages. v2 minor changes and Refs. adde
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