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Andrea Lionetto

Publications and source records attributed to Andrea Lionetto.

13 recordsLinked to original sources
arXiv2016

A Statistical Test of Walrasian Equilibrium by Means of Complex Networks Theory

We represent an exchange economy in terms of statistical ensembles for complex networks by introducing the concept of market configuration. This is defined as a sequence of nonnegative discrete random variables $\{w_{ij}\}$ describing the flow of a given commodity from agent $i$ to agent $j$. This sequence can be arranged in a nonnegative matrix $W$ which we can regard as the representation of a weighted and directed network or digraph $G$. Our main result consists in showing that general equilibrium theory imposes highly restrictive conditions upon market configurations, which are in most cases not fulfilled by real markets. An explicit example with reference to the e-MID interbank credit market is provided.

q-fin.GN↗
arXiv2012

Statistical ensembles for money and debt

We build a statistical ensemble representation of two economic models describing respectively, in simplified terms, a payment system and a credit market. To this purpose we adopt the Boltzmann-Gibbs distribution where the role of the Hamiltonian is taken by the total money supply (i.e. including money created from debt) of a set of interacting economic agents. As a result, we can read the main thermodynamic quantities in terms of monetary ones. In particular, we define for the credit market model a work term which is related to the impact of monetary policy on credit creation. Furthermore, with our formalism we recover and extend some results concerning the temperature of an economic system, previously presented in the literature by considering only the monetary base as conserved quantity. Finally, we study the statistical ensemble for the Pareto distribution.

q-fin.GN↗
arXiv2011

Dark Matter in Anomalous $U(1)'$ Models with neutral mixing

We study the lightest masses in the fermionic sector of an anomalous $U(1)'$ extension of the minimal supersymmetric standard model inspired by brane constructions. The LSP of this model is an XWIMP (extremely weak interaction particle) which is shown to have a relic density satisfying WMAP data. This computation is carried out numerically after having adapted the DarkSUSY package to our case.

hep-ph↗
arXiv2010

Stückelino Dark Matter in Anomalous U(1)' Models

We study a possible dark matter candidate in the framework of a minimal anomalous $U(1)'$ extension of the MSSM. It turns out that in a suitable decoupling limit the Stückelino, the fermionic degree of freedom of the Stückelberg multiplet, is the lightest supersymmetric particle (LSP). We compute the relic density of this particle including coannihilations with the next to lightest supersymmetric particle (NLSP) and with the next to next to lightest supersymmetric particle (NNLSP) which are assumed almost degenerate in mass. This assumption is needed in order to satisfy the stringent limits that the Wilkinson Microwave Anisotropy Probe (WMAP) puts on the relic density. We find that the WMAP constraints can be satisifed by different NLSP and NNLSP configurations as a function of the mass gap with the LSP. These results hold in the parameter space region where the model remains perturbative.

hep-ph↗
arXiv2010

Gaugino radiative decay in an anomalous U(1)' model

We study the neutralino radiative decay into the lightest supersymmetric particle (LSP) in the framework of a minimal anomalous U(1)' extension of the MSSM. It turns out that in a suitable decoupling limit the axino, which is present in the Stückelberg multiplet, is the LSP. We compute the branching ratio (BR) for the decay of a neutralino into an axino and a photon. We find that in a wide region of the parameter space, the BR is higher than 93% in contrast with the typical value (<=1%) in the CMSSM.

hep-ph↗
arXiv2009

On mass hierarchies in orientifold vacua

We analyze the problem of the hierarchy of masses and mixings in orientifold realizations of the Standard Model. We find bottom-up brane configurations that can generate such hierarchies.

hep-th↗
arXiv2008

Minimal Anomalous U(1)' Extension of the MSSM

We study an extension of the MSSM by an anomalous abelian vector multiplet and a Stückelberg multiplet. The anomalies are cancelled by the Green-Schwarz mechanism and the addition of Chern-Simons terms. The advantage of this choice over the standard one is that it allows for arbitrary values of the quantum numbers of the extra U(1). As a first step towards the study of hadron annihilations producing four leptons in the final state (a clean signal which might be studied at LHC) we then compute the decays $Z'\to Z_0 \g$ and $Z'\to Z_0 Z_0$. We find that the largest values of the decay rate is $\sim 10^{-4}$ GeV, while the expected number of events per year at LHC is at most of the order of 10.

hep-th↗
arXiv2006

Deflected Anomaly Mediation and Neutralino Dark Matter

We study the phenomenology of the neutralino dark matter in the so called deflected anomaly mediation scenario. This scheme is obtained from the minimal anomaly mediated scenario by introducing a gauge mediated sector with $N_f$ messenger fields. Unlike the former scheme the latter has no tachyons. We find that the neutralino is still the LSP in a wide region of the parameter space: it is essentially a pure bino in the scenario with $N_f=1$ while it can also be a pure higgsino for $N_f>1$. This is very different from the naive anomaly mediated scenario which predicts a wino like neutralino. Moreover we do not find any tachyonic scalars in this scheme. After computing the relic density (considering all the possible coannihilations) we find that there are regions in the parameter space with values compatible with the latest WMAP results with no need to consider moduli fields that decay in the early universe.

hep-ph↗
arXiv2006

Extra-Dimensions and Dark Matter

In this paper we study the general scenario of an effective theory coming from the compactification of a higher dimensional theory in a string inspired setting. This leads to gauge coupling unification at an intermediate mass scale. After having computed all the threshold corrections (due to Kaluza-Klein modes) to the running of the couplings of the MSSM we embark in a detailed phenomenological analysis of the model, based on the numerical package DarkSUSY, to find constraints on the scenario from Dark Matter data. The mass spectrum of the theory does not have tachyons. Moreover we find that the neutralino is still the LSP with a relic density compatible with the most recent experimental data. With respect to the standard mSUGRA scenario we find that the neutralino is higgsino like in most of the parameter space. Our modifications to the DarkSUSY package will be shortly available upon request.

hep-ph↗
arXiv2004

The Galactic Center as a Dark Matter Gamma-Ray Source

The EGRET telescope has identified a gamma-ray source at the Galactic center. We point out here that the spectral features of this source are compatible with the gamma-ray flux induced by pair annihilations of dark matter weakly interacting massive particles (WIMPs). We show that the discrimination between this interpretation and other viable explanations will be possible with GLAST, the next major gamma-ray telescope in space, on the basis of both the spectral and the angular signature of the WIMP-induced component. If, on the other hand, the data will point to an alternative explanation, we prove that there will still be the possibility for GLAST to single out a weaker dark matter source at the Galactic center. The potential of GLAST has been explored both in the context of a generic simplified toy-model for WIMP dark matter, and in a more specific setup, the case of dark matter neutralinos in the minimal supergravity framework. In the latter, we find that even in the case of moderate dark matter densities in the Galactic center region, there are portions of the parameter space which will be probed by GLAST.

astro-ph↗
arXiv2003

Supersymmetric Dark Matter with GLAST

We present a short review of the status of the dark matter problem. In particular we show that one of the best motivated candidate for the dark matter is the neutralino, a supersymmetric particle. Finally we study the possibility to detect gamma rays coming from neutralino pair annihilations that take place in our Galactic Center with the upcoming satellite detector GLAST.

astro-ph↗
arXiv2003

Search for Dark Matter with GLAST

The detection of exotic cosmic rays due to pair annihilation of dark matter particles in the Milky Way halo is a viable techniques to search for supersymmetric dark matter candidates. The study of the spectrum of gamma-rays, antiprotons and positrons offers good possibilities to perform this search in a significant portion of the Minimal Supersymmetric Standard Model parameter space. In particular the EGRET team have seen a convincing signal for a strong excess of emission from the Galactic center that has no simple explanation with standard processes. We will review the limits achievable with the experiment GLAST taking into accounts the LEP results and we will compare this method with the antiproton and positrons experiments.

astro-ph↗