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Giancarlo D'Ambrosio

Publications and source records attributed to Giancarlo D'Ambrosio.

At least 55 records · Page 3Linked to original sources
arXiv2004

CP, CPT and Rare Decays

We describe possible kaon physics goals to achieve with a high luminosity phi-factory. We motivate the relevance to improve the present bounds on CPT kaon physics quantities. Also, the interferometer machine phi-factory is useful to study CP violating/conserving effects in kaon decays. Thus we investigate K --> 3 pi amplitudes: charge asymmetries are interesting in charged kaon decays. In the case of neutral kaon decays one can study directely K_S --> 3 pi or interferences effects. Interference may also be used to study the CP even K_S -->pi+ pi- pi0 and final state interactions.

hep-ph↗
arXiv2004

Supersymmetric Dissipative Quantum Mechanics from Superstrings

Following the approach of Callan and Thorlacius applied to the superstring, we derive a supersymmetric extension of the non-local dissipative action of Caldeira and Leggett. The dissipative term turns out to be invariant under a group of superconformal transformations. When added to the usual kinetic term, it provides an example of supersymmetric dissipative quantum mechanics. As a by-product of our analysis, an intriguing connection to the homeotic/hybrid fermion model, proposed for CPT violation in neutrinos, appears.

hep-th↗
arXiv2003

Extracting short-distance physics from K_{L,S} -> pi0 e+ e- decays

We present a new analysis of the rare decay K_L -> pi0 e+ e- taking into account important experimental progress that has recently been achieved in measuring K_L -> pi0 gamma gamma and K_S -> pi0 e+ e-. This includes a brief review of the direct CP-violating component, a calculation of the indirect CP-violating contribution, which is now possible after the measurement of K_S -> pi0 e+ e-, and a re-analysis of the CP conserving part. The latter is shown to be negligible, based on experimental input from K_L -> pi0 gamma gamma, a more general treatment of the form factor entering the dispersive contribution, and on a comparison with the CP violating rate, which can now be estimated reliably. We predict B(K_L -> pi0 e+ e-) = (3.2 +1.2 -0.8) 10^{-11} in the Standard Model, dominated by CP violation with a sizable contribution (~40%) from the direct effect, largely through interference with the indirect one. Methods to deal with the severe backgrounds for K_L -> pi0 e+ e- using Dalitz-plot analysis and time-dependent K_L-K_S interference are also briefly discussed.

hep-ph↗
arXiv2003

Soft Leptogenesis

We study ``soft leptogenesis'', a new mechanism of leptogenesis which does not require flavour mixing among the right-handed neutrinos. Supersymmetry soft-breaking terms give a small mass splitting between the CP-even and CP-odd right-handed sneutrino states of a single generation and provide a CP-violating phase sufficient to generate a lepton asymmetry. The mechanism is successful if the lepton-violating soft bilinear coupling is unconventionally (but not unnaturally) small. The values of the right-handed neutrino masses predicted by soft leptogenesis can be low enough to evade the cosmological gravitino problem.

hep-ph↗
arXiv2003

Recent developments in rare kaon decays

We discuss issues in rare and radiative kaon decays. The interest is to extract useful short-distance information and uncover underlying dynamics. We emphasize channels where either we can understand non-perturbative aspects of QCD or there is a chance to test the Standard Model.

hep-ph↗
arXiv2002

Electromagnetic penguin operators and direct CP violation in K --> pi l^+ l^-

Supersymmetric extensions of the Standard Model predict a large enhancement of the Wilson coefficients of the dimension-five electromagnetic penguin operators affecting the direct CP violation in K_L --> pi^0 e^+ e^- and the charge asymmetry in K^\pm --> pi^\pm l^+ l^-. Here we compute the relevant matrix elements in the chiral quark model and compare these with the ones given by lattice calculations

hep-ph↗
arXiv2002

$K^+\to π^+ν\barν$: a rising star on the stage of flavour physics

Motivated by the new experimental information reported by the BNL--E787 Collaboration, we analyse the present impact and the future prospects opened by the measurement of $\br(K^+\toπ^+ν\barν)$. Although still affected by a large error, the BNL--E787 result favours values of $\br(K^+\to π^+ν\barν)$ substantially larger than what expected within the Standard Model. As a result, this data already provide non-trivial constraints on the unitarity triangle, when interpreted within the Standard Model framework. We stress the importance of the clean relation between $\br(K^+\to π^+ν\barν)$, $\sin2β$ and $ΔM_{B_d}/ΔM_{B_s}$ that in the next few years could provide one of the deepest probes of the Standard Model in the sector of quark-flavour dynamics. A speculative discussion about possible non-standard interpretations of a large $\br(K^+\to π^+ν\barν)$ is also presented. Two main scenarios naturally emerge: those with direct new-physics contributions to the $s \to d ν\barν$ amplitude and those with direct new-physics effects only in $B_d$--$\bar B_d$ mixing. Realistic models originating these two scenarios and possible future strategies to clearly identify them are briefly discussed.

hep-ph↗
arXiv2001

Long-distance contribution to the muon-polarization asymmetry in K^+\to π^+ μμ

We revisit the calculation of the long-distance contribution to the muon-polarization asymmetry Δ_{LR}, which arises, in K^+\toπ^+μ^+μ^-, from the two-photon intermediate state. The parity-violating amplitude of this process, induced by the local anomalous K^+π^-γ^*γ^* transition, is analysed; unfortunately, one cannot expect to predict its contribution to the asymmetry by using chiral perturbation theory alone. Here we evaluate this amplitude and its contribution to Δ_{LR} by employing a phenomenological model called the FMV model, in which the utility of the vector and axial-vector resonances exchange is important to soften the ultraviolet behaviour of the transition. We find that the long-distance contribution is of the same order of magnitude as the standard model short-distance contribution.

hep-ph↗
arXiv2001

Radiative rare kaon decays

We discuss theoretical issues in radiative rare kaon decays. The interest is twofold: to extract useful short-distance information and understand the underlying dynamics. We emphasize channels where either we can understand non-perturbative aspects of QCD or there is a chance to test the Standard Model.

hep-ph↗
arXiv2001

The diquark model: New Physics effects for charm and kaon decays

Motivated by diquark exchange, we construct a class of extensions of the standard model. These models can generate large CP conserving and CP violating contributions to the doubly Cabbibo suppressed decays D^0\to K^+π^- without affecting D^0-\overline{D^0} mixing, contrary to what is usually believed in the literature. We find an interesting specific realization of these models, which has the LR chiral structure and can induce novel density \times density operators. It is new for non-leptonic kaon decays, and particularly, may provide a possible solution to the ΔI=1/2 rule and direct CP violation, without inducing large flavour changing neutral currents.

hep-ph↗
arXiv2000

A phenomenological description of $K\toππγ$ magnetic transitions

A phenomenological analysis of $K\to ππγ$ ($K_L\toπ^+π^-γ$ and $K^+\toπ^+π^0γ$) with the direct emission photon is carried out beyond the leading order in the chiral perturbation theory. We show that the experimental evidence for the large photon energy dependence of the magnetic amplitude in $K_L\toπ^+π^-γ$ seems to indicate an interesting consequence: vector meson dominance must be implemented at $O(p^4)$, which is not a general feature of the chiral perturbation theory. The phenomenology of $K^+\toπ^+π^0γ$ is also analyzed using the same scheme.

hep-ph↗
arXiv2000

Radiative Rare Kaon Decays

We review some recent theoretical results on radiative rare kaon decays. Particular attention is devoted to the channels $K\to πl\bar{% l}$ and $K\to ππγ$, where we are (or might be) able to extract the short distance contributions. This is achieved by a careful study of the long distance part. We study also CP violating observables, which are sensitive also to extensions of the SM. As byproduct, we discuss interesting chiral tests.

hep-ph↗
arXiv2000

Theory of rare kaon decays

We review some recent theoretical results on rare kaon decays. Particular attention is devoted to find Standard Model tests. This is theoretically easy in $K\to πν\barν$, while a careful study of the long distance contributions is needed for $K_{L}\to π^{0}e% \bar{e}$, $K_{L}\to μ\barμ$ and $K\to ππγ$

hep-ph↗
arXiv1999

Rare kaon decays

We review some recent theoretical results on rare kaon decays. Particular attention is devoted to establish the short distance (direct CP violating) contribution to K_L => π^0 e \bar{e}. This is achieved by a careful study of the long distance part. As byproduct, we discuss interesting chiral tests.

hep-ph↗
arXiv1998

Analysis of K_L -> pi^+ pi^- gamma in Chiral Perturbation Theory

We study the long-distance dominated K_L -> pi^+ pi^- gamma decay at O(p^6) in Chiral Perturbation Theory. The complete calculation of the O(p^6) loop magnetic amplitude is carried out. At this chiral order the model dependent part of the vector meson exchange contribution to the magnetic amplitude is evaluated in the two models : FM (Factorization Model) and FMV (Factorization Model in the Vector Couplings). We predict, in an almost model independent way, a slope of K_L -> pi^+ pi^- gamma in the range c = -1.6,-1.8, consistently with the experimental value. We find that the experimental result for the width of K_L -> pi^+ pi^- gamma is compatible with a bigger breaking of the nonet symmetry in the weak vertices than previously stated. Thus we conclude that our analysis does not exclude an opposite sign to the one given by the dominance of the pion pole in the poorly known K_L -> gamma gamma amplitude. A complete analysis of the O(p^3) weak Vector-Pseudoscalar-Pseudoscalar (VPP) vertex is also performed.

hep-ph↗
arXiv1997

Spin-1 resonance contributions to the weak Chiral Lagrangian: the vector field formulation

We use the Vector formulation to evaluate vector and axial-vector exchange contributions to the O(p^4) weak Chiral Lagrangian. We recover in this framework the bulk of the contributions found previously by Ecker et al. in the antisymmetric formulation of vectors and axial-vectors, but new interesting features arise: i) most of our results are independent of Factorization and ii) novel contributions to non-leptonic kaon decays, proper of this formulation and phenomenologically interesting, are found. The phenomenological implications for K -> pi pi (pi) and radiative (anomalous and non-anomalous) non-leptonic kaon decays are thus investigated and found particularly relevant.

hep-ph↗
arXiv1997

Vector meson exchange contributions to K --> pi gamma gamma and K(L) -> gamma lepton+ lepton-

We have studied in the framework of Chiral Perturbation Theory (ChPT) the O(p^6) Vector Meson contributions to K -> pi gamma gamma and K(L) -> gamma gamma^*. We construct the most general ChPT lagrangian for the weak Vector-Pseudoscalar-Photon (VPgamma) vertex for K -> pi gamma gamma and K(L) -> gamma gamma^* and consequently we get the full structure of the O(p^6) local contributions generated by Vector Meson exchange. Then we compute new factorizable contributions to the weak VPgamma vertex generated by the odd-intrinsic parity violating lagrangian with no additional couplings. We find in fact a very nice agreement with the phenomenology of K -> pi gamma gamma and K(L) -> gamma gamma^*, more predictive power and a deeper understanding of the O(p^6) local operators. A novel interpretation of the K(L) -> gamma gamma^* data is given. Also a comparison with the existing models is presented.

hep-ph↗