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N. Di Bartolomeo

Publications and source records attributed to N. Di Bartolomeo.

17 recordsLinked to original sources
arXiv2015

The Extended Bess Model: Bounds from Precision Electroweak Measurements

We present an effective Lagrangian parameterization describing scalar, vector, and axial-vector bound states, originating from a strong breaking of the electroweak symmetry, based on the global symmetry $SU(N)_L\otimes SU(N)_R$. In this approach vector and axial-vector bound states are gauge bosons associated to a hidden $SU(N)_L\otimes SU(N)_R$ symmetry. After the gauging of the electroweak symmetry, the corrections to the self-energies of the standard model gauge bosons are calculated and bounds on the parameter space of the model arising from precision measurements are studied. The self-energy corrections arise from spin 1 mixings, pseudogoldstones loops, pseudogoldstone-spin 1 loops, and tadpole terms. The one-loop terms tend to decrease both isospin conserving and isospin violating corrections. Careful calculation for standard $SU(8)$ QCD-scaled technicolor shows that strictly this model (which has however serious theoretical difficulties on his own) is still marginally allowed at present experimental precision.

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↗
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

The fate of the leptophobic Z'

We review the main features of the leptophobic-Z' phenomenology, commenting on the prospects of these models after the recent experimental results on R_c, R_b and after the recent theoretical analyses of jet production at the Tevatron.

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

Rb, Rc and Jet Distributions at the Tevatron in a Model with an extra vector boson

We show that the reported anomalies in $R_b$ and $R_c$ can be interpreted as the effect of a heavy vector boson \zprime\ universally coupled to $u$- and $d$-type quarks separately and nearly decoupled from leptons. This extra vector boson could then also naturally explain the apparent excess of the jet rate at large transverse momentum observed at CDF.

hep-ph↗
arXiv1995

Strong coupling of excited heavy mesons

We compute the strong coupling constant $G_{B^{**} B π} \; (G_{D^{**} D π})$, where $B^{**}$ ($D^{**}$) is the $0^+$ $P-$wave $b \bar q \; (c \bar q)$ state, by QCD sum rules and by light-cone sum rules. The two methods give compatible results in the limit $m_Q \to \infty$, with a rather large value of the coupling constant. We apply the results to the calculation of the hadronic widths of the positive parity $B$ and $D$ states and to the chiral loop contribution to the ratio $f_{D_s}/f_D$.

hep-ph↗
arXiv1994

Heavy Meson Hyperfine Splitting: A Complete $1/m_Q$ Calculation

The hyperfine splittings $Δ_D=(m_{D^*_s}-m_{D_s})-(m_{D^{*+}}-m_{D^+})$ and $Δ_B=(m_{B^*_s}-m_{B_s})-(m_{B^{*0}}-m_{B^0})$ are analyzed in the framework of an effective lagrangian possessing chiral, heavy flavour and spin symmetries, explicitly broken by a complete set of first order terms. Among these terms, those responsible for the difference between the couplings $\gis$ and $\gi$ are evaluated in the QCD sum rules approach. Their contribution to $Δ_D$ and to $Δ_B$ appears to quantitatively balance previously estimated chiral effects nice agreement with the experimental data, solving a suspected puzzle for heavy quark theory.

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

Breaking Electroweak Symmetry Strongly

The problem of electroweak symmetry breaking is reviewed with discussion of future relevant experimentation at LHC and $e^+e^-$ linear colliders. The possibility of strong electroweak symmetry breaking is examined in more detail, using the BESS (Breaking Electroweak Symmetry Strongly) model as a basis for the discussion. The formal constructions are briefly presented and the possible expectations at future colliders are summarized.

hep-ph↗
arXiv1993

Effective lagrangian for B and D semileptonic decays

An effective lagrangian incorporating both chiral and heavy quark symmetries and describing the low momentum interactions of heavy mesons and light scalar and vector resonances is presented. Using some available data and assuming nearest pole dominance for the form factors we can calculate, at the leading order in chiral and heavy quark expansion, semileptonic $B$ and $D$ decays into light mesons.

hep-ph↗
arXiv1993

Two Body Non Leptonic Decays of B and B_s Mesons

We perform an analysis of two-body non leptonic decays of $B$ and $B_s$ mesons in the factorization approximation. We make use of the semileptonic decay amplitudes previously calculated on the basis of an effective lagrangian satisfying chiral and heavy quark symmetries and including spin 1 resonances. Exclusive semileptonic $D$-decay data are used as experimental input. Our results compare favorably with data, whenever they are available and indicate a positive value for the ratio of non leptonic coefficients $a_2/a_1$, similarly to previous studies.

hep-ph↗
arXiv1993

Effective Lagrangian for Heavy and Light Mesons: Radiative B Decays

We make use of the information obtained from semileptonic decays of $B$ and $D$ mesons, within an effective lagrangian description based on heavy quark theory and on chiral expansion, to study the radiative decays $B \to K^\star γ$ and $B_S \to ϕγ$, and the pair conversion processes $B \to K e^+e^-$ and $B \to K^\star e^+e^-$. We discuss with care the required extrapolations from zero recoils. We obtain a BR($B\to K^\starγ$) between $1.3\times 10^{-5}$ and $4.1\times 10^{-5}$ and BR($B_s \toϕγ$) between $1.4\times 10^{-5}$ and $4.5\times 10^{-5}$, with errors mainly arising from the present uncertainty in the Kobayashi-Maskawa element $|V_{ts}|$. For the pair conversion processes we study in particular the lepton effective mass distributions whose measurements would allow for an understanding both long distance and short distance contributions to such processes.

hep-ph↗
arXiv1993

Hadronic Transitions among Quarkonium States in a Soft-Exchange-Approximation. Chiral Breaking and Spin Symmetry Breaking Processes

Although no asymptotic heavy quark spin symmetry, and even more no flavor symmetry, are expected for systems such as quarkonium, a numerical discussion shows that for some processes and in a preasymptotic region which may roughly include charmonium and bottomonium, the use of the spin-symmetry may be useful in conjunction with chiral symmetry for light hadrons (soft-exchange- approximation regime, SEA). We continue our discussion of hadronic transitions in the SEA-regime by studying in particular chiral breaking transitions such as $~^3P' \to ~^3Pπ^0$, $~^3Pη$, level splittings and transitions which break both chiral and spin symmetry, such as $ψ' \to J/ψπ^0$, $J/ψη$, and $~^1P_1 \to J/ψπ^0$.

hep-ph↗
arXiv1992

Light Vector Resonances in the Effective Chiral Lagrangian for Heavy Mesons

We modify a chiral effective lagrangian recently suggested to describe interactions of the light pseudoscalars with mesons containing a heavy quark, so as to incorporate light vector resonances, such as $ρ$, etc. The modification uses the hidden gauge symmetry approach. As a preliminary example we present an application to the semileptonic $D\to K^\star$ decay.

hep-ph↗