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A. Deandrea

Publications and source records attributed to A. Deandrea.

At least 73 records · Page 4Linked to original sources
arXiv1998

A Constituent Quark-Meson Model for Heavy Meson Decays

I describe a model for heavy meson decays based on an effective quark-meson lagrangian. I consider the heavy mesons S with spin and parity J^P=(1+,0+), H with J^P=(1-,0-) and T^mu with J^P=(2+,1+), i.e. S and P wave heavy-light mesons. The model is constrained by the known symmetries of QCD in the mQ -> infinity limit for the heavy quarks, and chiral symmetry in the light quark sector. Using a very limited number of free parameters it is possible to compute several phenomenological quantities, e.g. the leptonic B and B** decay constants; the three universal Isgur-Wise form factors: xi, tau(3/2), tau(1/2), describing the semi-leptonic decays B -> D(*) l nu, B -> D** l nu; the strong and radiative D* decays; the weak semi-leptonic decays of B and D into light mesons: pi, rho, a1. An overall agreement with data, when available, is achieved.

hep-ph↗
arXiv1998

A Constituent Quark-Meson Model for Heavy-Meson Processes

We describe the effective heavy meson lagrangian for S- and P-wave heavy-light mesons in terms of a model based on meson-quark interactions, where mesonic transition amplitudes are represented by diagrams with heavy mesons attached to loops containing heavy and light constituent quarks. The model is relativistic and incorporates the heavy quark symmetries. The universal form factors of the heavy meson transition amplitudes are calculated together with their slopes and compared to existing data and limits. As further applications of the model, strong and radiative decays of D* and B* are considered. The agreement with data is surprisingly good and shows that the model offers a viable alternative to effective meson lagrangians which require a larger number of input parameters.

hep-ph↗
arXiv1998

A Strong Electroweak Sector at Future mu^+ mu^- Colliders

We discuss the prospects for detecting at a muon collider the massive new vector resonances V and light pseudo-Nambu-Goldstone bosons P of a typical strongly interacting electroweak sector (as represented by the BESS model). Expected sensitivities to V's at a high energy collider are evaluated and the excellent prospects for discovering P's via scanning at a low energy collider are delineated.

hep-ph↗
arXiv1997

Atomic parity violation in cesium and implications for new physics

Recent high-precision measurements of atomic parity-nonconserving transitions between the 6S and 7S states of cesium allow for a determination of the weak nuclear charge with a precision of 1.3%, providing an improved test of the standard model at low energy. Implications for new physics are examined in terms of low energy effects on the weak charge, in particular contact interactions and scalar leptoquark limits. Prospects for further improvements are described.

hep-ph↗
arXiv1997

Manifestation of a strong electroweak sector with decoupling at hadronic colliders

We study the expected phenomenology at present (Tevatron) and future (Tevatron Upgrade, LHC) hadronic colliders of a model describing a strong electroweak symmetry breaking sector with both vector and axial vector strong interacting bosons degenerate in mass. Due to decoupling, this model at low energies is almost indistinguishable from the Standard Model, passing therefore all low energy precision tests at LEPI. We will show that it gives quite visible signals at forthcoming hadronic accelerators. The new charged vector bosons can be detected more easily than the neutral ones.

hep-ph↗
arXiv1997

Non Leptonic Heavy Hadron Decays and Local Duality

We discuss local duality for weak non leptonic B and Lambda_b decays in the m_b -> infinity limit under the hypothesis of factorization and in the Shifman-Voloshin limit. We show that, under these hypotheses, local duality holds for the first two terms in the 1/m_b expansion and at the order alpha_s in the perturbative expansion. The possible relevance of these results for the operator product expansion evaluation of the b-hadron lifetimes is discussed.

hep-ph↗
arXiv1996

Phenomenology of Heavy Meson Chiral Lagrangians

The approximate symmetries of Quantum ChromoDynamics in the infinite heavy quark ($Q=c,b$) mass limit ($m_Q \to \infty$) and in the chiral limit for the light quarks ($m_q \to 0,\;q=\,u,\,d,\,s$) can be used together to build up an effective chiral lagrangian for heavy and light mesons describing strong interactions among effective meson fields as well as their couplings to electromagnetic and weak currents, including the relevant symmetry breaking terms. The effective theory includes heavy ($Q \bar q$) mesons of both negative and positive parity, light pseudoscalars, as well as light vector mesons. We summarize the estimates for the parameters entering the effective lagrangian and discuss in particular some phenomenologically important couplings, such as $g_{B^* B π}$. The hyperfine splitting of heavy mesons is discussed in detail. The effective lagrangian allows for the possibility to describe consistently weak couplings of heavy ($B,\, D$) to light ($π,\, ρ, \, K^*,\,$ etc.) mesons. The method has however its own limitations, due to the requirement that the light meson momenta should be small, and we discuss how such limitations can be circumvented through reasonable ansatz on the form factors. Flavour conserving (e. g. $B^* \to B\, γ$) and flavour changing (e. g. $B \to K^* \, γ$) radiative decays provide another field of applications of effective lagrangians; they are discussed together with their phenomenological implications. Finally we analyze effective lagrangians describing heavy charmonium- like ($\bar Q Q$) mesons and their strong and electromagnetic interactions. The role of approximate heavy quark symmetries for this case and the phenomenological tests of these models are also discussed.

hep-ph↗
arXiv1996

A Strong Electroweak Sector at Future Linear Colliders

An effective lagrangian describing a strong interacting electroweak sector is considered. It contains new vector and axial-vector resonances all degenerate in mass and mixed with $W$ and $Z$. The model, for large mass of these degenerate gauge bosons, becomes identical to the standard model in the classical limit of infinite Higgs mass. The limits on the parameter space of this model from future $e^+e^-$ colliders are presented.

hep-ph↗
arXiv1996

Searches For New Physics

Review of prospects for discovery of new physics signals at LEP2. The areas covered include SUSY, exotic fermions, BESS models, leptoquarks, virtual effects and CP violating observables.

hep-ph↗
arXiv1995

Degenerate BESS Model: The possibility of a low energy strong electroweak sector

We discuss possible symmetries of effective theories describing spinless and spin 1 bosons, mainly to concentrate on an intriguing phenomenological possibility: that of a hardly noticeable strong electroweak sector at relatively low energies. Specifically, a model with both vector and axial vector strong interacting bosons may possess a discrete symmetry imposing degeneracy of the two sets of bosons (degenerate BESS model). In such a case its effects at low energies become almost invisible and the model easily passes all low energy precision tests. The reason lies essentially in the fact that the model automatically satisfies decoupling, contrary to models with only vectors. For large mass of the degenerate spin one bosons the model becomes identical at the classical level to the standard model taken in the limit of infinite Higgs mass. For these reasons we have thought it worthwhile to fully develop the model, together with its possible generalizations, and to study the expected phenomenology. For instance, just because of its invisibility at low energy, it is conceivable that degenerate BESS has low mass spin one states and gives quite visible signals at existing or forthcoming accelerators.

hep-ph↗
arXiv1995

Some Results on the BESS Model at Future Colliders

We present some results on the usefulness of upgraded Tevatron, LHC proton proton collider and linear e+e- colliders in the TeV range to test the idea of a strongly interacting sector as responsible for the electroweak symmetry breaking. The calculations are performed within an effective lagrangian description, called the BESS model, which provides for a rather general frame based on the standing point of custodial symmetry and gauge invariance, without specifying any dynamical scheme.

hep-ph↗
arXiv1995

SYMMETRIES FOR VECTOR AND AXIAL-VECTOR MESONS

We discuss the possible symmetries of the effective lagrangian describing interacting pseudoscalar-, vector-, and axial-vector mesons. Specific choices of the parameters give rise to an $[SU(2)\otimes SU(2)]^3$ symmetry. This symmetry can be obtained either {\it á la} Georgi, with all states in the spectrum remaining massless, or in a new realization, implying decoupling of the pseudoscalar bosons from degenerate vector and axial-vector mesons. This second possibility, when minimally coupled with $SU(2)\otimes U(1)$ electroweak gauge vector bosons, seems particularly appealing. All deviations in the low-energy electroweak parameters are strongly suppressed, and the vector and axial-vector states turn out to be quite narrow. A nearby strong electroweak sector would then be conceivable and in principle it could be explored with relatively low energy accelerators.

hep-ph↗
arXiv1994

The Bess Model at Future Colliders

The BESS model consists of an effective lagrangian parametrization with dynamical symmetry breaking, describing scalar, vector and axial-vector bound states in a rather general framework. After a brief description of the model and its generalizations, predictions for physics at future accelerators are given both for LHC and e+e- machines. Contribution to the proceedings of the First Arctic Workshop on Future Physics and Accelerators, Saariselkä, Finland, August 1994.

hep-ph↗
arXiv1994

On the coupling of heavy mesons to pions in QCD

We compute the strong coupling constant $g_{P^* P π}$, with $P$ and $P^*$ respectively pseudoscalar and vector heavy mesons by using the QCD sum rules approach. Our computation is based on the evaluation of the time ordered product of currents between the vacuum and the soft pion state. The so-called parasitic terms are taken into account and give a contribution to the sum rule of the same order of the lowest lying state, while higher dimension non perturbative terms have small numerical effects. The infinite heavy quark mass limit is also examined.

hep-ph↗
arXiv1994

Pseudo Goldstones at Future Colliders from the Extended Bess Model

We consider the production of the lightest pseudo-Goldstone bosons at future colliders through the vector resonances predicted by the extended BESS model, which consists of an effective lagrangian parametrization with dynamical symmetry breaking, describing scalar, vector and axial-vector bound states in a rather general framework. We find that the detection of pseudo-Goldstone pairs at LHC requires a careful evaluation of backgrounds. For e+e- collisions in the TeV range the backgrounds can be easily reduced and the detection of pseudo-Goldstone pairs is generally easier.

hep-ph↗
arXiv1993

Non Leptonic Two Body Decays of B Mesons

Within the framework of the factorization approximation, two body non-leptonic decays of $B$ mesons are related to semileptonic matrix elements and form factors, evaluated with an effective lagrangian incorporating both chiral and heavy quark symmetries. Using semileptonic $D$-decay data, estimates for nonleptonic processes are obtained.

hep-ph↗