Correlations and realistic interactions in doubly closed shell nuclei

We review the latest variational calculations of the ground state properties of doubly closed shell nuclei, from $^{12}$C to $^{208}$Pb, with semirealistic and realistic two- and three-nucleon interactions. The studies are carried on within the framework of the correlated basis function theory and integral equations technique, with state dependent correlations having central and tensor components. We report results for the ground state energy, one- and two-body densities and static structure functions. For $^{16}$O and $^{40}$Ca we use modern interactions and find that the accuracy of the method is comparable to that attained in nuclear matter with similar hamiltonians, giving nuclei underbound by $\sim$2 MeV/A. The computed Coulomb sums are in complete agreement with the latest analysis of the experimental data.Comment: 11 Latex pages, 2 ps figures. Talk delivered at the 10th International Conference on Recent Progress In Many-Body Theories, Seattle 1999. To appear in "Advances in Quantum Many-Body Theory", vol.3, World Scientifi

Multiphoton signals of a (96 GeV?) stealth boson

Cascade decays of new scalars into final states with multiple photons and possibly quarks may lead to distinctive experimental signatures at high-energy colliders. Such signals are even more striking if the scalars are highly boosted, as when produced from the decay of a much heavier resonance. We study this type of events within the framework of the minimal stealth boson model, an anomaly-free $\text{U}(1)_{Y'}$ extension of the Standard Model with two complex scalar singlets. It is shown that, while those signals may have cross sections that might render them observable with LHC Run 2 data, they have little experimental coverage. We also establish a connection with a CMS excess observed in searches for new scalars decaying into diphoton final states near 96 GeV. In particular, we conclude that the predicted multiphoton signatures are compatible with such excess.Comment: LaTeX 32 pages. Comments added and discussions extended. Final version in EPJ

Multilepton production via top flavour-changing neutral couplings at the CERN LHC

Zt and gamma t production with Z -> l+ l- and t -> Wb -> l nu b provides the best determination of top flavour-changing neutral couplings at the LHC. The bounds on tc couplings eventually derived from these processes are similar to those expected from top decays, while the limits on tu couplings are better by a factor of two. The other significant Z and W decay modes are also investigated.Comment: 30 pages, 23 PS figures. Uses epsfig.sty and elsart.sty. Added some references and corrected some typos. Added more comments about statistics. Using elsart.sty reduces the size to 30 pages. Published in Nucl. Phys.

A closer look at the possible CMS signal of a new gauge boson

The CMS collaboration has recently reported a 2.8$\sigma$ excess of $eejj$ events with an invariant mass around 2 TeV. This observation can be explained in the context of standard model extensions with new gauge bosons $W'$, $Z'$ and heavy neutrinos coupling (mainly) to the electron. We discuss additional signals that allow to confirm or discard the $W'$ and $Z'$ hypotheses.Comment: ReVTeX 5 page

Constraints on the Wtb vertex from early LHC data

We use the recent measurements of top quark decay asymmetries in ATLAS and the t-channel single top cross section in CMS to set the first combined LHC limits on the Wtb vertex. This combination allows to obtain much better limits than the separate measurements. The resulting constraints are comparable, although still weaker, than the ones obtained using Tevatron data with much more statistics.Comment: RevTeX 4 page

Shedding light on the ttˉt \bar t asymmetry: the photon handle

We investigate a charge asymmetry in $t \bar t \gamma$ production at the LHC that provides complementary information to the measured asymmetries in $t \bar t$ production. We estimate the experimental uncertainty in its measurement at the LHC with 8 and 14 TeV. For new physics models that simultaneously reproduce the asymmetry excess in $t \bar t$ at the Tevatron and the SM-like asymmetry at the LHC, the measurement in $t \bar t \gamma$ at the LHC could exhibit significant deviations with respect to the SM prediction.Comment: LaTeX 15 page

Top effective operators at the ILC

We investigate the effect of top trilinear operators in t tbar production at the ILC. We find that the sensitivity to these operators largely surpasses the one achievable by the LHC either in neutral or charged current processes, allowing to probe new physics scales up to 4.5 TeV for a centre of mass energy of 500 GeV. We show how the use of beam polarisation and an eventual energy upgrade to 1 TeV allow to disentangle all effective operator contributions to the Ztt and gamma tt vertices.Comment: LaTeX 13 pages. Typos corrected. Final version in JHE