arXiv subjects

Andrea Mammarella

Publications and source records attributed to Andrea Mammarella.

11 recordsLinked to original sources

arXiv2017

Meson Physics in Asymmetric Matter

This paper describes dynamic and thermodynamic (at $T=0$) properties of mesons in asymmetric matter in the framework of Chiral Perturbation Theory. We consider a mesonic system at vanishing temperature with nonzero isospin chemical potential and strangeness chemical potential and we study their effect on the phase diagram. We also study meson masses and mixing in the resulting normal phase, pion condensation phase and kaon condensation phase. We find differences with previous papers regarding meson masses and mixing in the condensed phases; the results presented here are supported by theory group analysis and direct calculations. Pressure, density and equation of state of the system at $T=0$ and nonzero $μ_I$ are calculated, finding remarkable agreement with analogue studies performed by lattice calculations.

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arXiv2017

Scrutinizing the pion condensed phase

When the isospin chemical potential exceeds the pion mass, charged pions condense in the zero-momentum state forming a superfluid. Chiral perturbation theory provides a very powerful tool for studying this phase. However, the formalism that is usually employed in this context does not clarify various aspects of the condensation mechanism and makes the identification of the soft modes problematic. We re-examine the pion condensed phase using different approaches within the chiral perturbation theory framework. As a first step, we perform a low-density expansion of the chiral Lagrangian valid close to the onset of the Bose-Einstein condensation. We obtain an effective theory that can be mapped to a Gross-Pitaevskii Lagrangian in which, remarkably, all the coefficients depend on the isospin chemical potential. The low-density expansion becomes unreliable deep in the pion condensed phase. For this reason, we develop an alternative field expansion deriving a low-energy Lagrangian analog to that of quantum magnets. By integrating out the "radial" fluctuations we obtain a soft Lagrangian in terms of the Nambu-Goldstone bosons arising from the breaking of the pion number symmetry. Finally, we test the robustness of the second-order transition between the normal and the pion condensed phase when next-to-leading-order chiral corrections are included. We determine the range of parameters for turning the second-order phase transition into a first-order one, finding that the currently accepted values of these corrections are unlikely to change the order of the phase transition.

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arXiv2016

Equation of state of imbalanced cold matter from chiral perturbation theory

We study the thermodynamic properties of matter at vanishing temperature for non-extreme values of the isospin chemical potential and of the strange quark chemical potential. From the leading order pressure obtained by maximizing the static chiral Lagrangian density we derive a simple expression for the equation of state in the pion condensed phase and in the kaon condensed phase. We find an analytical expression for the maximum of the ratio between the energy density and the Stefan-Boltzmann energy density as well as for the isospin chemical potential at the peak both in good agreement with lattice simulations of quantum chromodynamics. We speculate on the location of the crossover from the Bose-Einstein condensate state to the Bardeen-Cooper-Schrieffer state by a simple analysis of the thermodynamic properties of the system. For $μ_I \gtrsim 2 m_π$ the leading order chiral perturbation theory breaks down; as an example it underestimates the energy density of the system and leads to a wrong asymptotic behavior.

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arXiv2015

Intriguing aspects of meson condensation

We analyze various aspects of pion and kaon condensation in the framework of chiral perturbation theory. Considering a system at vanishing temperature and varying the isospin chemical potential and the strange quark chemical potential we reproduce known results about the phase transition to the pion condensation phase and to the kaon condensation phase. However, we obtain mesonic mixings and masses in the condensed phases that are in disagreement with the results reported in previous works. Our findings are obtained both by a theory group analysis and by direct calculation by means of the same low-energy effective Lagrangian used in previous works. We also study the leptonic decay channels in the normal phase and in the pion condensed phase, finding that some of these channels have a peculiar nonmonotonic behavior as a function of the isospin chemical potential. Regarding the semileptonic decays, we find that that they should be efficient feeding processes for the stable charged pion state.

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arXiv2015

Aspects of Meson Condensation

In this work pion and kaon condensation in the framework of chiral perturbation theory is studied. I consider a system at vanishing temperature with nonzero isospin chemical potential and strangeness chemical potential; meson masses and mixing in the normal phase, the pion condensation phase and the kaon condensation phase are described. There are differences with previous works, but the results presented here are supported by both theory group analysis and by direct calculations. Some pion decay channels in the normal and the pion condensation phases are studied, finding a nonmonotonic behavior of the $Γ$ decay width as a function of $μ_I$.

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arXiv2012

Asymmetry at LHC for an U(1)' anomalous extension of MSSM

The measurement of the forward-backward asymmetry at LHC could be an important instrument to pinpoint the features of extra neutral gauge particles obtained by an extension of the gauge symmetry group of the standard model. For definitiveness, in this work we consider an extension of the gauge group of the Minimal Supersymmetric Standard Model by an extra anomalous U(1) gauge symmetry (MiAUMSSM). We focus on pp -> e+e- at LHC and use four different definitions of the asymmetry obtained implementing four different cuts on the directions and momenta of the final states of our process of interest. The calculations are performed without imposing constraints on the charges of the extra Z's of our model, since the anomaly is cancelled by a Green-Schwarz type mechanism. Our final result is a fit of our data with a polynomial in the charges from which to extract the values of the charges given the experimental result.

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arXiv2012

Anomalous U(1) and Asymmetry

In the past years many possible extensions of the Standard Model (SM) have been investigated. If one of this model is revealed at the LHC, we will need tools to distinguish it among the many others studied. One possibility to achieve this goal is to utilize the forward-backward asymmetry. In this paper we calculate the asymmetry for a model in which there is an extra U(1) anomalous symmetry. Furthermore, we show that the asymmetry can be used to impose constraints on the free parameters of the model.

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arXiv2012

Anomalous U(1), Dark Matter and Asymmetry

In this thesis we study the phenomenology of an anomalous U(1) extension of the MSSM. We briefly introduce the concept of Supersymmetry and describe the MSSM, then we introduce our extended model, describing its main properties. Then it starts the original part of the thesis. First there is the study of the model in the most general case, in which there is mixing between the SM U(1) and the anomalous U(1). This is followed by the calculation of all the vertices and the amplitudes that are of interest for the phenomenology that we are going to study. After describing in details how the Boltzmann Equation gives the relic density of particle species, we use it and the amplitudes of our model already calculated to study if the neutralinos introduced by our model can be viable candidates to describe the Dark Matter relic density. We have found that this is the case only if the anomalous candidate coannihilates with a MSSM neutralino. In the case of no mixing between the U(1)s we have obtained this results performing analytical calculations, whom results we show for many mass gaps. To obtain the same result in the mixing case we have modified the DarkSUSY package. This has also permitted us to obtain more precise informations about the dependence of the relic density on the various free parameters of the model. We show many plots containing these results. In the last part of the thesis we study the Asymmetry at the LHC for our model. We start introducing the Forward-Backward Asymmetry then we move on to describe how it can be utilized at the LHC. We introduce different possible definitions and describe their properties, then we calculate their predicted values in our model. Finally we explain how these results could be used to impose constraints over theoretical models that describe beyond the Standard Model physics.

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arXiv2012

Anomalous $U(1)'$ and Dark Matter

We have studied the lightest masses in the fermionic sector of an anomalous $U(1)'$ extension of the Minimal Supersymmetric Standard Model (MSSM) inspired by brane constructions. The LSP of this model is an XWIMP (extremely weak interaction particle). We have studied its relic density in the cases in which there is mixing with the neutralinos of the MSSM and in the case in which there is not such mixing. We have showed that this extended model can satisfy the WMAP data. To perform this calculation we have modified the DarkSUSY package.

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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.

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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.

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