Diphotons at the ZZ-pole in Models of the 750 GeV Resonance Decaying to Axion-Like Particles

Models in which the 750 GeV resonance ($S$) decays to two light axion-like particles (ALPs $a$), which in turn decay to collimated photons mimicking the observed signal, are motivated by Hidden Valley scenarios and could also provide a mechanism by which a $S \to \gamma \gamma$ signal persists while $S \to Z \gamma,\; ZZ$ and $WW$ remain subdued in the near future. We point out that these Hidden Valley like models invoking $S \to aa \to 4 \gamma$ must also contend with $Z \to a (\to \gamma \gamma) \gamma$ constraints coming from CDF and ATLAS. Within an effective field theory framework, we work out the constraints on the couplings of $S$ to $a$ and gauge bosons coming from photonic $Z$ decays and ensuring that the ALPs decay inside the electromagnetic calorimeter, in two regimes - where $a$ decays primarily to photons, and where $a$ also has hadronic branchings. The analysis is done for both when $S$ has a large as well as a narrow width, and for different relative contributions to the signal coming from $S \to \gamma \gamma$ and $a \to \gamma \gamma$. Results for the particular case where $S$ and $a$ belong to the same complex field are also presented. A $\gamma\gamma$ resonance at the $Z$-pole coming from $Z \to a \gamma$ is expected in this class of models. Taking benchmark ALP masses below around 0.4 GeV and, assuming reasonable values for the fake jet rate and the identification efficiency of the photon-jet, we find the prospects for the discovery of diphotons at the $Z$-pole.Comment: 19 pages, 11 figure

The 750 GeV SS-cion: Where else should we look for it?

The resonance $S$ at $\sim 750$ GeV in the diphoton channel observed by ATLAS and CMS, if it holds up, is almost certainly the ($S$)cion of a larger dynasty in a UV completion that may very well be connected to the hierarchy problem. At this stage, however, an effective field theory framework provides a useful way to parametrize searches for this resonance in other channels. Assuming that the excess is due to a new scalar or pseudoscalar boson, we study associated production of $S$ ("$S$-strahlung") at the LHC and propose searches in several clean channels like $\gamma\gamma\ell\ell$, \gamma\gamma\ell\eslash and \ell\ell\ell\gamma\eslash to probe dimension-5 operators coupling $S$ to Standard Model gauge bosons. We consider a range of widths for $S$, from 5 GeV to 45 GeV, and find that the three channels probe complementary regions of parameter space and the suppression scale $\Lambda$. The finding of most immediate relevance is that with 3 fb$^{-1}$, the LHC might already reveal new excesses in the $\gamma\gamma\ell\ell$ channel and a 5(3) $\sigma$ discovery may already be possible after collecting 65(25) fb$^{-1}$ of data with \ell\ell\ell\gamma\eslash events if the scale of the new physics is within $\sim$ 9 TeV for couplings respecting 8 TeV LHC bounds and compatible with the observed excess in diphotons for a wide resonance as suggested by the ATLAS Collaboration. Beyond the EFT parametrization, we found realizations of models with heavy vector-like quarks and leptons which can simultaneously fit the diphoton excess and be discovered in the channels proposed here.Comment: 11 pages, 2 tables, 5 figures. References and comments added. Version accepted for publication in Physics Letters

Maximum Entropy Inferences on the Axion Mass in Models with Axion-Neutrino Interaction

In this work we use the Maximum Entropy Principle (MEP) to infer the mass of an axion which interacts to photons and neutrinos in an effective low energy theory. The Shannon entropy function to be maximized is suitably defined in terms of the axion branching ratios. We show that MEP strongly constrains the axion mass taking into account the current experimental bounds on the neutrinos masses. Assuming that the axion is massive enough to decay into all the three neutrinos and that MEP fixes all the free parameters of the model, the inferred axion mass is in the interval $0.1\$eV$\ <m_{A}<0.2$ eV, which can be tested by forthcoming experiments such as IAXO. However, even in the case where MEP fixes just the axion mass and no other parameter, we found that $0.1$ eV $< m_A < 6.3$ eV in the DFSZ model with right-handed neutrinos. Moreover, a light axion, allowed to decay to photons and the lightest neutrino only, is determined by MEP as a viable dark matter candidate.Comment: 13 pages, 5 figures, typos corrected, figures update

Inferences on the Higgs Boson and Axion Masses through a Maximum Entropy Principle

The Maximum Entropy Principle (MEP) is a method that can be used to infer the value of an unknown quantity in a set of probability functions. In this work we review two applications of MEP: one giving a precise inference of the Higgs boson mass value; and the other one allowing to infer the mass of the axion. In particular, for the axion we assume that it has a decay channel into pairs of neutrinos, in addition to the decay into two photons. The Shannon entropy associated to an initial ensemble of axions decaying into photons and neutrinos is then built for maximization.Comment: Contributed to the 13th Patras Workshop on Axions, WIMPs and WISPs, Thessaloniki, May 15 to 19, 201

Exact Renormalization of Massless QED2

We perform the exact renormalization of two-dimensional massless gauge theories. Using these exact results we discuss the cluster property and confinement in both the anomalous and chiral Schwinger models.Comment: 14 pages, no figures, introduction and conclusions modifie

Pedido de declaração de insolvência por outro legitimado : exercício do direito de ação ou abuso de direito de ação?

Sumário: 1. Introdução: 1.1. Situação de insolvência; 1.2. Critérios de definição da situação de insolvência; 2. O pedido de declaração de insolvência por outro legitimado. 3. O direito de ação e os seus limites; 4. A litigância de má-fé; 5. O abuso de direito de ação; 6. A responsabilidade pela ação ou culpa in agendo no requerimento do pedido de declaração de insolvência; 7. Conclusões