6,129 research outputs found
Effective axial-vector coupling of gluon as an explanation to the top quark asymmetry
We explore the possibility that the large forward-backward
asymmetry measured by the CDF detector at Tevatron could be due to a universal
effective axial-vector coupling of gluon. Using an effective field theory
approach we show model independently how such a log-enhanced coupling occurs at
1-loop level. The interference with QCD gluon vector coupling naturally induces
the observed positive forward-backward asymmetry that grows with
invariant mass and is consistent with the cross section measurements.
This scenario does not involve new flavor changing couplings nor operators that
interfere with QCD, and, therefore, is not constrained by the LHC searches for
4-quark contact interactions. We predict top quark polarization effects that
grow with energy and allow to test this scenario at the LHC. Our proposal
offers a viable alternative to new physics scenarios that explain the
forward-backward asymmetry anomaly with the interference between QCD and tree
level new physics amplitudes.Comment: Few small changes in the text, same as published version, 5 pages, 2
figure
Experimental Constraints on the Neutralino-Nucleon Cross Section
In the light of recent experimental results for the direct detection of dark
matter, we analyze in the framework of SUGRA the value of the
neutralino-nucleon cross section. We study how this value is modified when the
usual assumptions of universal soft terms and GUT scale are relaxed. In
particular we consider scenarios with non-universal scalar and gaugino masses
and scenarios with intermediate unification scale. We also study superstring
constructions with D-branes, where a combination of the above two scenarios
arises naturally. In the analysis we take into account the most recent
experimental constraints, such as the lower bound on the Higgs mass, the branching ratio, and the muon .Comment: References added, bsgamma upper bound improved, results unchanged,
Talk given at Corfu Summer Institute on Elementary Particle Physics, August
31-September 20, 200
Onsager reciprocity relations without microscopic reversibility
In this paper we show that Onsager--Machlup time reversal properties of
thermodynamic fluctuations and Onsager reciprocity relations for transport
coefficients can hold also if the microscopic dynamics is not reversible. This
result is based on the explicit construction of a class of conservative models
which can be analysed rigorously.Comment: revtex, no figure
A perturbative approach to the Bak-Sneppen Model
We study the Bak-Sneppen model in the probabilistic framework of the Run Time
Statistics (RTS). This model has attracted a large interest for its simplicity
being a prototype for the whole class of models showing Self-Organized
Criticality. The dynamics is characterized by a self-organization of almost all
the species fitnesses above a non-trivial threshold value, and by a lack of
spatial and temporal characteristic scales. This results in {\em avalanches} of
activity power law distributed. In this letter we use the RTS approach to
compute the value of , the value of the avalanche exponent and the
asymptotic distribution of minimal fitnesses.Comment: 4 pages, 3 figures, to be published on Physical Review Letter
Gender equality attitudes of Muslim migrants in Italy
In European public debates, Islam is often described as having a determinant role on gender inequality. However, Islamic community in Italy is significantly diversified and gender-related attitudes are affected by the different contexts of origin. By using multipurpose Istat data, we estimate a synthetic index of gender equality attitudes and conduct multivariate empirical analyses on migrant Muslim men and women. Results show that the heterogeneity among migrant groups persists after controlling for other factors. In addition, more religious Muslims are on average more opposed to gender equality. However, the role of religious communal integration is more important than that of individual religiosity
Large deviation approach to non equilibrium processes in stochastic lattice gases
We present a review of recent work on the statistical mechanics of non
equilibrium processes based on the analysis of large deviations properties of
microscopic systems. Stochastic lattice gases are non trivial models of such
phenomena and can be studied rigorously providing a source of challenging
mathematical problems. In this way, some principles of wide validity have been
obtained leading to interesting physical consequences.Comment: Extended version of the lectures given by G. Jona-Lasinio at the 9th
Brazilian school of Probability, August 200
Quantitative analysis of Clausius inequality
In the context of driven diffusive systems, for thermodynamic transformations
over a large but finite time window, we derive an expansion of the energy
balance. In particular, we characterize the transformations which minimize the
energy dissipation and describe the optimal correction to the quasi-static
limit. Surprisingly, in the case of transformations between homogeneous
equilibrium states of an ideal gas, the optimal transformation is a sequence of
inhomogeneous equilibrium states.Comment: arXiv admin note: text overlap with arXiv:1404.646
Minimum dissipation principle in stationary non equilibrium states
We generalize to non equilibrium states Onsager's minimum dissipation
principle. We also interpret this principle and some previous results in terms
of optimal control theory. Entropy production plays the role of the cost
necessary to drive the system to a prescribed macroscopic configuration
Dynamics in the Fitness-Income plane: Brazilian states vs World countries
In this paper we introduce a novel algorithm, called Exogenous Fitness, to calculate the Fitness of subnational entities and we apply it to the states of Brazil. In the last decade, several indices were introduced to measure the competitiveness of countries by looking at the complexity of their export basket. Tacchella et al (2012) developed a non-monetary metric called Fitness. In this paper, after an overview about Brazil as a whole and the comparison with the other BRIC countries, we introduce a new methodology based on the Fitness algorithm, called Exogenous Fitness. Combining the results with the Gross Domestic Product per capita (GDPp), we look at the dynamics of the Brazilian states in the Fitness-Income plane. Two regimes are distinguishable: one with high predictability and the other with low predictability, showing a deep analogy with the heterogeneous dynamics of the World countries. Furthermore, we compare the ranking of the Brazilian states according to the Exogenous Fitness with the ranking obtained through two other techniques, namely Endogenous Fitness and Economic Complexity Index
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