Departamento de FĂsica
https://repositorio.unifesp.br/handle/11600/41321
2020-02-22T05:05:50ZMaximum Entropy Inferences on the Axion Mass in Models with Axion-Neutrino Interaction
https://repositorio.unifesp.br/handle/11600/51493
Maximum Entropy Inferences on the Axion Mass in Models with Axion-Neutrino Interaction
Alves, Alexandre [UNIFESP]; Dias, Alex Gomes; da Silva, Roberto
In this work, we use the maximum entropy principle (MEP) to infer the mass of an axion which interacts to photons and neutrinos in an effective low energy theory. The Shannon entropy function to be maximized is defined in terms of the axion branching ratios. We show that MEP strongly constrains the axion mass taking into account the current experimental bounds on the neutrinos masses. Assuming that the axion is massive enough to decay into all the three neutrinos and that MEP fixes all the free parameters of the model, the inferred axion mass is in the interval 0.1 eV < m(A) < 0.2 eV, which can be tested by forthcoming experiments such as IAXO. However, even in the case where MEP fixes just the axion mass and no other parameter, we found that 0.1 eV < m(A) < 6.3 eV in the DFSZ model with right-handed neutrinos. Moreover, a light axion, allowed to decay to photons and the lightest neutrino only, is determined by MEP as a viable dark matter candidate.
2017-01-01T00:00:00ZCan we discover double Higgs production at the LHC?
https://repositorio.unifesp.br/handle/11600/51376
Can we discover double Higgs production at the LHC?
Alves, Alexandre [UNIFESP]; Ghosh, Tathagata; Sinha, Kuver
We explore double Higgs production via gluon fusion in the b (b) over bar gamma gamma channel at the high-luminosity LHC using machine learning tools. We first propose a Bayesian optimization approach to select cuts on kinematic variables, obtaining a 30%-50% increase in the significance compared to current results in the literature. We show that this improvement persists once systematic uncertainties are taken into account. We next use boosted decision trees (BDT) to further discriminate signal and background events. Our analysis shows that a joint optimization of kinematic cuts and BDT hyperparameters results in an appreciable improvement in the significance. Finally, we perform a multivariate analysis of the output scores of the BDT. We find that assuming a very low level of systematics, the techniques proposed here will be able to confirm the production of a pair of standard model Higgs bosons at 5 sigma level with 3 ab(-1) of data. Assuming a more realistic projection of the level of systematics, around 10%, the optimization of cuts to train BDTs combined with a multivariate analysis delivers a respectable significance of 4.6 sigma. Even assuming large systematics of 20%, our analysis predicts a 3.6 sigma significance, which represents at least strong evidence in favor of double Higgs production. We carefully incorporate background contributions coming from light flavor jets or c jets being misidentified as b jets and jets being misidentified as photons in our analysis.
2017-01-01T00:00:00ZBayesian analysis of CCDM models
https://repositorio.unifesp.br/handle/11600/51281
Bayesian analysis of CCDM models
Jesus, J. F.; Valentim, R. [UNIFESP]; Andrade-Olivera, F.
Creation of Cold Dark Matter (CCDM), in the context of Einstein Field Equations, produces a negative pressure term which can be used to explain the accelerated expansion of the Universe. In this work we tested six different spatially flat models for matter creation using statistical criteria, in light of SNe Ia data: Akaike Information Criterion (AIC), Bayesian Information Criterion (BIC) and Bayesian Evidence (BE). These criteria allow to compare models considering goodness of fit and number of free parameters, penalizing excess of complexity. We find that JO model is slightly favoured over LJO/Lambda CDM model, however, neither of these, nor Gamma = 3 alpha H-0 model can be discarded from the current analysis. Three other scenarios are discarded either because poor fitting or because of the excess of free parameters. A method of increasing Bayesian evidence through reparameterization in order to reducing parameter degeneracy is also developed.
2017-01-01T00:00:00ZMillisecond direct measurement of the magnetocaloric effect of a fe2p-based compound by the mirage effect
https://repositorio.unifesp.br/handle/11600/49196
Millisecond direct measurement of the magnetocaloric effect of a fe2p-based compound by the mirage effect
Cugini, F.; Porcari, G.; Viappiani, C.; Caron, L.; dos Santos, A. O.; Cardoso, L. P.; Passamani, E. C.; Proveti, J. R. C.; Gama, Sergio [UNIFESP]; Bruck, E.; Solzi, M.
We present direct measurements of the magnetocaloric effect on a Fe2P-based compound induced by a milliseconds pulsed magnetic field of 1 T to test their possible use in high frequency (up to 100 Hz) thermomagnetic cycles. The reported measurements were performed with an innovative and versatile non-contact set up based on the mirage effect. The adiabatic temperature change of a MnFeP0.45As0.55 sample is presented and compared with measurements performed varying the same magnetic field in a time interval of 1 s and 100 ms. These results demonstrate the absence of kinetic constraints in the first-order phase transition of this sample induced on the milliseconds time scale. The study of the materials' response to millisecond magnetic field pulses represents a fundamental test for the development of more powerful and efficient magnetic refrigerators. (C) 2016 AIP Publishing LLC.
2016-01-01T00:00:00Z