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

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$_5$ 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

Cosmological Consequences of Nearly Conformal Dynamics at the TeV scale

Nearly conformal dynamics at the TeV scale as motivated by the hierarchy problem can be characterized by a stage of significant supercooling at the electroweak epoch. This has important cosmological consequences. In particular, a common assumption about the history of the universe is that the reheating temperature is high, at least high enough to assume that TeV-mass particles were once in thermal equilibrium. However, as we discuss in this paper, this assumption is not well justified in some models of strong dynamics at the TeV scale. We then need to reexamine how to achieve baryogenesis in these theories as well as reconsider how the dark matter abundance is inherited. We argue that baryonic and dark matter abundances can be explained naturally in these setups where reheating takes place by bubble collisions at the end of the strongly first-order phase transition characterizing conformal symmetry breaking, even if the reheating temperature is below the electroweak scale $\sim 100$ GeV. We also discuss inflation as well as gravity wave smoking gun signatures of this class of models.Comment: 22 pages, 7 figure

Simple and Realistic Composite Higgs Models in Flat Extra Dimensions

We construct new composite Higgs/gauge-Higgs unification (GHU) models in flat space that overcome all the difficulties found in the past in attempting to construct models of this sort. The key ingredient is the introduction of large boundary kinetic terms for gauge (and fermion) fields. We focus our analysis on the electroweak symmetry breaking pattern and the electroweak precision tests and show how both are compatible with each other. Our models can be seen as effective TeV descriptions of analogue warped models. We point out that, as far as electroweak TeV scale physics is concerned, one can rely on simple and more flexible flat space models rather than considering their unavoidably more complicated warped space counterparts. The generic collider signatures of our models are essentially undistinguishable from those expected from composite Higgs/warped GHU models, namely a light Higgs, colored fermion resonances below the TeV scale and sizable deviations to the Higgs and top coupling.Comment: 30 figures, 9 figures; v2: minor improvements, one reference added, version to appear in JHE

Model-Independent Bounds on a Light Higgs

We present up-to-date constraints on a generic Higgs parameter space. An accurate assessment of these exclusions must take into account statistical, and potentially signal, fluctuations in the data currently taken at the LHC. For this, we have constructed a straightforward statistical method for making full use of the data that is publicly available. We show that, using the expected and observed exclusions which are quoted for each search channel, we can fully reconstruct likelihood profiles under very reasonable and simple assumptions. Even working with this somewhat limited information, we show that our method is sufficiently accurate to warrant its study and advocate its use over more naive prescriptions. Using this method, we can begin to narrow in on the remaining viable parameter space for a Higgs-like scalar state, and to ascertain the nature of any hints of new physics---Higgs or otherwise---appearing in the data.Comment: 32 pages, 10 figures; v3: correction made to basis of four-derivative operators in the effective Lagrangian, references adde

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