5,176 research outputs found

### Constraints on a general 3-generation neutrino mass matrix from neutrino data: application to the MSSM with R-parity violation

We consider a general symmetric $(3\times 3)$ mass matrix for three
generations of neutrinos. Imposing the constraints, from the atmospheric
neutrino and solar neutrino anomalies as well as from the CHOOZ experiment, on
the mass squared differences and on the mixing angles, we identify the ranges
of allowed inputs for the 6 matrix elements. We apply our results to Majorana
left-handed neutrino masses generated at tree level and through
fermion--sfermion loop diagrams in the MSSM with R-parity violation. The
present experimental results on neutrinos from laboratories, cosmology and
astrophysics are implemented to either put bounds on trilinear ($\lambda_{ijk},
\lambda'_{ijk}$) and bilinear
($\mu_{e,\mu,\tau}$) R-parity-violating couplings or constrain combinations
of products of these couplings.Comment: 35 pages, 25 PS figures, REVTeX, revised version to appear in Nuclear
physics

### Evolution of quantum observables: from non-commutativity to commutativity

A fundamental aspect of the quantum-to-classical limit is the transition from a non-
commutative algebra of observables to commutative one.However, this transition is not possible if we only consider unitary evolutions. One way to describe this transition is to consider the Gamow vectors, which introduce exponential decays in the evolution. In this paper, we give two mathematical models in which this transition happens in the infinite time limit. In the first one, we consider operators acting on the space of the Gamow vectors, which represent quantum resonances. In the second one, we use an algebraic formalism from scattering theory. We construct a non-commuting algebra which commutes in the infinite time limit.MINECO Grant MTM2014- 57129-C2-1-P. Junta de Castilla y Leon Grants BU229P18, VA137G18

### Two-loop dimensional reduction and effective potential without temperature expansions

In many extensions of the Standard Model, finite temperature computations are
complicated by a hierarchy of zero temperature mass scales, in addition to the
usual thermal mass scales. We extend the standard thermal resummations to such
a situation, and discuss the 2-loop computations of the Higgs effective
potential, and an effective 3d field theory for the electroweak phase
transition, without carrying out high or low temperature expansions for the
heavy masses. We also estimate the accuracy of the temperature expansions
previously used for the MSSM electroweak phase transition in the presence of a
heavy left-handed stop. We find that the low temperature limit of dealing with
the left-handed stop is accurate up to surprisingly high temperatures.Comment: 20 pages; small clarifications added; to appear in Nucl.Phys.

### Efficiency of Human Activity on Information Spreading on Twitter

Understanding the collective reaction to individual actions is key to
effectively spread information in social media. In this work we define
efficiency on Twitter, as the ratio between the emergent spreading process and
the activity employed by the user. We characterize this property by means of a
quantitative analysis of the structural and dynamical patterns emergent from
human interactions, and show it to be universal across several Twitter
conversations. We found that some influential users efficiently cause
remarkable collective reactions by each message sent, while the majority of
users must employ extremely larger efforts to reach similar effects. Next we
propose a model that reproduces the retweet cascades occurring on Twitter to
explain the emergent distribution of the user efficiency. The model shows that
the dynamical patterns of the conversations are strongly conditioned by the
topology of the underlying network. We conclude that the appearance of a small
fraction of extremely efficient users results from the heterogeneity of the
followers network and independently of the individual user behavior.Comment: 29 pages, 10 figure

### Constraints on both bilinear and trilinear R-parity violating couplings from neutrino laboratories and astrophysics data

We consider neutrino masses generated at tree level and at one loop, through fermion--sfermion loop diagrams, in the MSSM with R-parity violation. Using the $(3\times 3)$ mass and mixing matrices for three generations of neutrinos and the present experimental results on neutrinos from laboratories and astrophysics simultaneously, we put bounds on both trilinear ($\lambda_{ijk}, \lambda'_{ijk}$) and bilinear ($\mu_{e},\mu_\mu,\mu_\tau$) R-parity-violating couplings

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