arXiv subjects

Stefano Morisi

Publications and source records attributed to Stefano Morisi.

At least 37 records · Page 2Linked to original sources

arXiv2020

Decaying dark matter at IceCube and its signature on High Energy gamma experiments

The origin of neutrino flux observed in IceCube is still mainly unknown. Typically two flux components are assumed, namely: atmospheric neutrinos and an unknown astrophysical term. In principle the latter could also contain a top-down contribution coming for example from decaying dark matter. In this case one should also expect prompt and secondary gammas as well. This leads to the possibility of a multimessenger analysis based on the simultaneous comparison of the Dark Matter hypothesis both with neutrino and high energy gamma rays data. In this paper, we analyze, for different decaying Dark Matter channels, the 7.5 years IceCube HESE data, and compare the results with previous exclusion limits coming from Fermi data. Finally, we test whether the Dark Matter hypothesis could be further scrutinised by using forthcoming high energy gamma rays experiments.

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arXiv2018

Investigating two heavy neutral leptons neutrino seesaw mechanism at SHiP

One of the main purposes of SHiP experiment is to shed light on neutrino mass generation mechanisms like the so-called seesaw. We consider a minimal type-I seesaw neutrino mass mechanism model with two heavy neutral leptons (right-handed or sterile neutrinos) with arbitrary masses. Extremely high active-sterile mixing angle requires a correlation between the phases of the Dirac neutrino couplings. Actual experimental limits on the half-life of neutrinoless double beta decay $0νββ$-rate on the active-sterile mixing angle are not significative for SHiP.

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arXiv2018

Neutrinophilic Dark Matter in the epoch of IceCube and Fermi-LAT

The recent observation of the blazar TXS 0506+056 suggests the presence of a hard power-law component in the extraterrestrial TeV-PeV neutrino flux, in agreement with the IceCube analysis on the 8-year through-going muon neutrinos from the Northern Sky. This is slightly in tension with the soft power-law neutrino flux deduced by the IceCube 6-year High Energy Starting Events data. A possible solution to such a puzzle is assuming a two-component neutrino flux. In this paper, we focus on the case where, in addition to an astrophysical power-law, the second component is a pure neutrino line produced by decaying Dark Matter particles. We investigate how to realize a neutrinophilic decaying Dark Matter in an extension of the Standard Model. The main features of the model are: i) the requirement of a new symmetry like a global $U(1)$ charge; ii) the Dirac nature of active neutrinos; iii) a low-reheating temperature of the Universe of about 1 TeV. We perform a likelihood statistical analysis to fit the IceCube data according to the present Fermi-LAT gamma-rays constraints.

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arXiv2018

Neutrino phenomenology from leptogenesis

Assuming a type-I seesaw mechanism for neutrino mass generation and invoking a baryogengesis via leptogenesis scenario, we consider a reasonable hierarchical structure for Dirac neutrino mass matrix, similar to up-type quark mass matrix. These hypotheses imply a relevant connection between high scale CP violation and low energy one. By requiring a compact heavy neutrino mass spectrum, which allows to circumvent Davidson-Ibarra limit, one can obtain an efficient leptogenesis restricting the allowed region for low energy neutrino parameters. Once the oscillating parameters are taken inside a $3σ$ range, through the numerical resolution of the leptogenesis Boltzmann equations one gets the following allowed intervals for the lightest neutrino mass and the Dirac CP phase: $-0.90π<δ<-0.75π$ and $m_1\sim( 0.002 - 0.004)$ eV.

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arXiv2018

Use of ANTARES and IceCube data to constrain a single power-law neutrino flux

We perform the first statistical combined analysis of the diffuse neutrino flux observed by ANTARES (nine-year) and IceCube (six-year) by assuming a single astrophysical power-law flux. The combined analysis reduces by a few percent the best-fit values for the flux normalization and the spectral index. Both data samples show an excess in the same energy range (40--200 TeV), suggesting the presence of a second component. We perform a goodness-of-fit test to scrutinize the null assumption of a single power-law, scanning different values for the spectral index. The addition of the ANTARES data reduces the $p$-value by a factor 2$÷$3. In particular, a single power-law component in the neutrino flux with the spectral index deduced by the six-year up-going muon neutrinos of IceCube is disfavored with a $p$-value smaller than $10^{-2}$.

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arXiv2017

Interpreting IceCube 6-year HESE data as an evidence for hundred TeV decaying Dark Matter

The assumption of a single astrophysical power-law flux to explain the IceCube 6-year HESE extraterrestrial events yields a large spectral index that is in tension with gamma-ray observations and the 6-year up-going muon neutrinos data. Adopting a spectral index belonging to the range $\left[2.0,2.2\right]$, which is compatible with the one deduced by the analysis performed on the 6-year up-going muon neutrinos data and with $p$-$p$ astrophysical sources, the latest IceCube data show an up to $2.6\,σ$ excess in the number of events in the energy range 40--200 TeV. We interpret such an excess as a decaying Dark Matter signal and we perform a likelihood-ratio statistical test to compare the two-component scenario with respect to the single-component one.

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arXiv2016

The LHC diphoton resonance from gauge symmetry

Motivated by what is possibly the first sign of new physics seen at the LHC, the diphoton excess at $750$ GeV in ATLAS and CMS, we present a model that provides naturally the necessary ingredients to explain the resonance. The simplest phenomenological explanation for the diphoton excess requires a new scalar state, $X(750)$, as well as additional vector-like (VL) fermions introduced in an ad-hoc way in order to enhance its decays into a pair of photons and/or increase its production cross-section. We show that the requiered VL quarks and their couplings can emerge naturally from a complete framework based on the $SU(3)_L \otimes U(1)_\mathcal{X}$ gauge symmetry.

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arXiv2016

Low energy IceCube data and a possible Dark Matter related excess

In this Letter we focus our attention on the IceCube events in the energy range between 60 and 100 TeV, which show an order 2-sigma excess with respect to a power-law with spectral index 2. We analyze the possible origin of such an excess by comparing the distribution of the arrival directions of IceCube events with the angular distributions of simply distributed astrophysical galactic/extragalactic sources, as well as with the expected flux coming from DM interactions (decay and annihilation) for different DM profiles. The statistical analysis performed seems to disfavor the correlation with the galactic plane, whereas rules out the DM annihilation scenario only in case of small clumpiness effect. The small statistics till now collected does not allow to scrutinize the cases of astrophysical isotropic distribution and DM decay scenarios. For this reason we perform a forecast analysis in order to stress the role of future Neutrino Telescopes.

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arXiv2016

Decaying Leptophilic Dark Matter at IceCube

We present a novel interpretation of IceCube high energy neutrino events (with energy larger than 60 TeV) in terms of an extraterrestrial flux due to two different contributions: a flux originated by known astrophysical sources and dominating IceCube observations up to few hundreds TeV, and a new flux component where the most energetic neutrinos come from the leptophilic three-body decays of dark matter particles with a mass of few PeV. Differently from other approaches, we provide two examples of elementary particle models that do not require extremely tiny coupling constants. We find the compatibility of the theoretical predictions with the IceCube results when the astrophysical flux has a cutoff of the order of 100 TeV (broken power law). In this case the most energetic part of the spectrum (PeV neutrinos) is due to an extra component such as the decay of a very massive dark matter component. Due to the low statistics at our disposal we have considered for simplicity the equivalence between deposited and neutrino energy, however such approximation does not affect dramatically the qualitative results. Of course, a purely astrophysical origin of the neutrino flux (no cutoff in energy below the PeV scale - unbroken power law) is still allowed. If future data will confirm the presence of a sharp cutoff above few PeV this would be in favor of a dark matter interpretation.

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arXiv2015

Chances for SUSY-GUT in the LHC Epoch

The magic couple of SUSY and GUT still appears the most elegant and predictive physics concept beyond the Standard Model. Since up to now LHC found no evidence for supersymmetric particles it becomes of particular relevance to determine an upper bound of the energy scale they have to show up. In particular, we have analyzed a generic SUSY-GUT model assuming one step unification like in SU(5), and adopting naturalness principles, we have obtained general bounds on the mass spectrum of SUSY particles. We claim that if a SUSY gauge coupling unification takes place, the lightest gluino or Higgsino cannot have a mass larger than about 20 TeV. Such a limit is of interest for planning new accelerator machines.

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arXiv2015

Relating quarks and leptons with the T7 flavour group

In this letter we present a model for quarks and leptons based on T7 as flavour symmetry, predicting a canonical mass relation between charged leptons and down-type quarks proposed earlier. Neutrino masses are generated through a Type-I seesaw mechanism, with predicted correlations between the atmospheric mixing angle and neutrino masses. Compatibility with oscillation results lead to lower bounds for the lightest neutrino mass as well as for the neutrinoless double beta decay rates, even for normal neutrino mass hierarchy.

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arXiv2014

Radiative neutrino mass in 331 scheme

We propose a new radiative mechanism for neutrino mass generation based on the 3-3-1 electroweak gauge group. Lepton number is a symmetry of the Yukawa sector but spontaneously broken in the gauge sector. As a result light Majorana masses arise from neutral gauge boson exchange at the one-loop level. In addition to the isosinglet neutrinos which may be produced at the LHC through the extended gauge boson "portals", the model contains new isosinglet quarks which can also lie at the TeV scale and provide a plethora of collider phenomena.

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arXiv2014

Inflation and majoron dark matter in the seesaw mechanism

We propose that inflation and dark matter have a common origin, connected to the neutrino mass generation scheme. As a model we consider spontaneous breaking of global lepton number within the seesaw mechanism. We show that it provides an acceptable inflationary scenario consistent with the recent CMB B-mode observation by the BICEP2 experiment. The scheme may also account for the baryon asymmetry of the Universe through leptogenesis for reasonable parameter choices.

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arXiv2014

The low-scale approach to neutrino masses

In this short review we revisit the broad landscape of low-scale $SU(3)_c \times SU(2)_L \times U(1)_Y$ models of neutrino mass generation, with view on their phenomenological potential. This includes signatures associated to direct neutrino mass messenger production at the LHC, as well as messenger-induced lepton flavor violation processes. We also briefly comment on the presence of WIMP cold dark matter candidates.

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arXiv2014

Common origin of reactor and sterile neutrino mixing

If the hints for light sterile neutrinos from short-baseline anomalies are to be taken seriously, global fits indicate active-sterile mixings of a magnitude comparable to the known reactor mixing. We therefore study the conditions under which the active-sterile and reactor mixings could have the same origin in an underlying flavour model. As a starting point, we use $μ-τ$ symmetry in the active neutrino sector, which (for three neutrinos) yields a zero reactor neutrino angle and a maximal atmospheric one. We demonstrate that adding one sterile neutrino can change this setting, so that the active-sterile mixing and non-zero $θ_{13}$ can be generated simultaneously. From the phenomenological perspective, electron (anti)neutrino disappearance can be easily accommodated, while muon neutrino disappearance can vanish. It is, however, difficult to reconcile the LSND results with this scenario. From the theory perspective, the setting requires the misalignment of some of the flavon vacuum expectation values, which may be achieved in an $A_4$ or $D_4$ flavour symmetry model using extra dimensions.

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arXiv2014

Neutrino Mass and Mixing: from Theory to Experiment

The origin of fermion mass hierarchies and mixings is one of the unresolved and most difficult problem in high-energy physics. One possibility to address the flavour problem is by extending the Standard Model to include a family symmetry. In the recent years it has become very popular to use non-Abelian discrete flavour symmetries because of their power in the prediction of the large leptonic mixing angles relevant for neutrino oscillation experiments. Here we give an introduction to the flavour problem and to discrete groups which have been used to attempt a solution for it. We review the current status of models in the light of the recent measurement of the reactor angle and we consider different model building directions taken. The use of the flavons or multi Higgs scalars in model building is discussed as well as the direct vs. indirect approaches. We also focus on the possibility to distinguish experimentally flavour symmetry models by means of mixing sum rules and mass sum rules. In fact, we illustrate in this review the complete path from mathematics, via model building, to experiments, so that any reader interested to start working in the field could use this text as a starting point in order to get a broad overview of the different subject areas.

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arXiv2014

Higher Dimensional Effective Operators for Direct Dark Matter Detection

We discuss higher dimensional effective operators describing interactions between fermionic dark matter and Standard Model particles. They are typically suppressed compared to the leading order effective operators, which can explain why no conclusive direct dark matter detection has been made so far. The ultraviolet completions of the effective operators, which we systematically study, require new particles. These particles can potentially have masses at the TeV scale and can therefore be phenomenologically interesting for LHC physics. We demonstrate that the lowest order options require Higgs-portal interactions generated by dimension six operators. We list all possible tree-level completions with extra fermions and scalars, and we discuss the LHC phenomenology of a specific example with extra heavy fermion doublets.

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arXiv2012

Split neutrinos - leptogenesis, dark matter and inflation

We propose a simple framework to split neutrinos with a slight departure from tribimaximal mixing - where two of the neutrinos are Majorana type which provide thermal leptogenesis. The Dirac neutrino with a tiny Yukawa coupling explains primordial inflation and the cosmic microwave background radiation, where the inflaton is the gauge invariant flat direction. The observed baryon asymmetry, and the scale of inflation are intimately tied to the observed reactor angle, which can be further constrained by the LHC and the neutrinoless double beta decay experiments. The model also provides the lightest right handed sneutrino as a part of the inflaton to be the dark matter candidate.

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