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Nemevsek M.,ICTP | Nemevsek M.,Jozef Stefan Institute | Senjanovic G.,ICTP | Tello V.,International School for Advanced Studies | Tello V.,Arnold Sommerfeld Center
Physical Review Letters | Year: 2013

Probing the origin of neutrino mass by disentangling the seesaw mechanism is one of the central issues of particle physics. We address it in the minimal left-right symmetric model and show how the knowledge of light and heavy neutrino masses and mixings suffices to determine their Dirac Yukawa couplings. This in turn allows one to make predictions for a number of high and low energy phenomena, such as decays of heavy neutrinos, neutrinoless double beta decay, electric dipole moments of charged leptons, and neutrino transition moments. We also discuss a way of reconstructing the neutrino Dirac Yukawa couplings at colliders such as the LHC. © 2013 American Physical Society.


Tello V.,International School for Advanced Studies | Nemevek M.,ICTP | Nemevek M.,Jozef Stefan Institute | Nesti F.,University of Ferrara | And 2 more authors.
Physical Review Letters | Year: 2011

The Large Hadron Collider has the potential to probe the scale of left-right symmetry restoration and the associated lepton number violation. Moreover, it offers the hope of measuring the right-handed leptonic mixing matrix. We show how this, together with constraints from lepton flavor violating processes, can be used to make predictions for neutrinoless double beta decay. We illustrate this connection in the case of the type-II seesaw. © 2011 American Physical Society.


Di Giuseppe F.,ECMWF | Molteni F.,ECMWF | Tompkins A.M.,ICTP
Quarterly Journal of the Royal Meteorological Society | Year: 2013

A spatially based precipitation bias correction is introduced that generalizes existing approaches. The method consists of projecting observed precipitation anomalies on to the model's modes of variability for a large set of model hindcasts to produce artificial mapped empirical orthogonal functions, which are used to bias correct forecasts. Similar to previous spatially based methods, the scheme can shift displaced anomalies, associated with the West African monsoon progression for example, to their correct location, and by construction produces a corrected field with a zero-mean bias with respect to the observations. The new method has the advantage that it only applies corrections to modes of variability for which the model has proven skill, and does not rely on a one-to-one direct correspondence between the observational and model modes, a restriction of previous methods. By processing the precipitation fields in sequences of seven pentad averages, it is also possible to including variability on shorter than monthly time-scales, important if the end product is to be used for end-user impact-focused research. The method is tested for various empirical orthogonal function-defined climate macro regions within Africa and is shown to reduce biases while also improving threat skill scores over a range of thresholds and forecast lead times. © 2012 Royal Meteorological Society.


News Article | December 15, 2016
Site: www.eurekalert.org

The inaugural Walter Kohn Prize for quantum-mechanical materials and molecular modeling has been awarded to Professor Yanming Ma, a researcher from Jilin University in Changchun, China. The prize recognizes his development of efficient methods for the determination of crystal structures based on density functional theory and for the prediction of novel phases of materials under high pressure. The prize was established in March 2016 by the Abdus Salam International Centre for Theoretical Physics (ICTP) and the Quantum ESPRESSO Foundation in honor of Chemistry Nobel Laureate Walter Kohn, a leading condensed matter physicist who developed density functional theory (DFT), a method that drastically reduces the amount of computing power needed to model the properties of complex materials, without compromising the accuracy of a model's simulations. DFT has already had a big impact on a wide variety of fields, including chemistry, molecular physics, medicine and engineering. It also has opened the door to contributions from scientists from disadvantaged countries who have no access to huge supercomputers, due to its low computing costs and the wide availability of open source modeling software. Professor Ma is a rising star in the quantum-mechanical materials modeling world. His work has featured noteworthy examples of many different aspects of computational materials science: developing novel algorithms, performing virtual experiments, and the in silico design of materials with useful properties. "Yanming Ma is an outstanding scientist, but also an inspiration to students in China," said ICTP condensed matter physicist Sandro Scandolo, who is also a representative member of the Quantum ESPRESSO Foundation. "We are happy that the inaugural prize goes to such an outstanding scientist--it sets the standards high." "Professor Ma's work has applications as diverse as the design of functional materials--superconductive, superhard, or thermoelectric materials--and the stability of matter at extreme conditions," says Stefano Baroni, professor in the Condensed Matter section at the International School for Advanced Studies (SISSA) and founding director of the Quantum ESPRESSO Foundation. "Not only has Professor Ma authored countless publications, he is also the main developer of an open source software package (nicknamed CALYPSO), thus making his methodology available to a broad scientific audience." The Quantum ESPRESSO Foundation is the home of some of the most popular and internationally recognized open source codes for quantum-mechanical materials modeling, based on DFT. ICTP regularly organizes schools with the foundation, especially in developing countries. Professor Ma will receive the Prize at a ceremony to be held 13 January 2017 at ICTP, during the Centre's International Workshop on Computational Physics and Materials Science. For more details about the prize, visit the Walter Kohn Prize web page. About ICTP: The Abdus Salam International Centre for Theoretical Physics (ICTP) supports theoretical and applied physics research, as well as training and educational opportunities for scientists from the developing world. Over the past five decades, scientists from 188 countries have made over 140,000 visits to ICTP to learn about the latest findings in their fields, returning to their native countries to share what they have learned. ICTP has been a major force in stemming the scientific brain drain from the developing world. More details at http://www. . About Quantum ESPRESSO Foundation: The foundation fosters and supports the design, implementation, maintenance, and free dissemination of high-quality, high-performance open-source scientific software for ab-initio quantum numerical modeling of materials. More details at http://foundation. .


Cicoli M.,ICTP | Cicoli M.,National Institute of Nuclear Physics, Italy | Conlon J.P.,Rudolf Peierls Center for Theoretical Physics | Quevedo F.,ICTP | Quevedo F.,University of Cambridge
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We consider reheating driven by volume modulus decays in the LARGE volume scenario. Such reheating always generates nonzero dark radiation through the decays to the axion partner, while the only competitive visible sector decays are Higgs pairs via the Giudice-Masiero term. In the framework of sequestered models where the cosmological moduli problem is absent, the simplest model with a shift-symmetric Higgs sector generates 1.56≤ΔNeff≤1.74. For more general cases, the known experimental bounds on ΔNeff strongly constrain the parameters and matter content of the models. © 2013 American Physical Society.


Braun A.P.,King's College | Collinucci A.,Free University of Colombia | Valandro R.,ICTP | Valandro R.,National Institute of Nuclear Physics, Italy
Journal of High Energy Physics | Year: 2014

U(1) gauge symmetries in F-theory are expected to manifest themselves as codimension three singularities of Calabi-Yau fourfolds. However, some of these are known to become massive at strong coupling via the Stückelberg mechanism. In this note, we propose a geometric picture for detecting all U(1)'s, and determining which ones are massive and which ones are massless. We find that massive gauge symmetries show up as codimension three singularities that only admit small, non-Kähler, resolutions. Our proposal passes several highly non-trivial tests, including a case with a non-diagonal mass matrix. © 2014 The Author(s).


Mitra M.,National Institute of Nuclear Physics, Italy | Senjanovic G.,ICTP | Vissani F.,National Institute of Nuclear Physics, Italy
Nuclear Physics B | Year: 2012

The experimental rate of neutrinoless double beta decay can be saturated by the exchange of virtual sterile neutrinos, that mix with the ordinary neutrinos and are heavier than 200 MeV. Interestingly, this hypothesis is subject only to marginal experimental constraints, because of the new nuclear matrix elements. This possibility is analyzed in the context of the Type I seesaw model, performing also exploratory investigations of the implications for heavy neutrino mass spectra, rare decays of mesons as well as neutrino-decay search, LHC, and lepton flavor violation. The heavy sterile neutrinos can saturate the rate only when their masses are below some 10 TeV, but in this case, the suppression of the light-neutrino masses has to be more than the ratio of the electroweak scale and the heavy-neutrino scale; i.e., more suppressed than the naive seesaw expectation. We classify the cases when this condition holds true in the minimal version of the seesaw model, showing its compatibility (1) with neutrinoless double beta rate being dominated by heavy neutrinos and (2) with any light neutrino mass spectra. The absence of excessive fine-tunings and the radiative stability of light neutrino mass matrices, together with a saturating sterile neutrino contribution, imply an upper bound on the heavy neutrino masses of about 10 GeV. We extend our analysis to the Extended seesaw scenario, where the light and the heavy sterile neutrino contributions are completely decoupled, allowing the sterile neutrinos to saturate the present experimental bound on neutrinoless double beta decay. In the models analyzed, the rate of this process is not strictly connected with the values of the light neutrino masses, and a fast transition rate is compatible with neutrinos lighter than 100 meV. © 2011 Elsevier B.V.


Senjanovic G.,ICTP
International Journal of Modern Physics A | Year: 2011

I argue that LHC may shed light on the nature of neutrino mass through the probe of the seesaw mechanism. The smoking gun signature is lepton number violation through the production of same sign lepton pairs, a collider analogy of the neutrinoless double beta decay. I discuss this in the context of left-right symmetric theories, which led originally to neutrino mass and the seesaw mechanism. A WR gauge boson with a mass in a few TeV region could easily dominate neutrinoless double beta decay, and its discovery at LHC would have spectacular signatures of parity restoration and lepton number violation. Moreover, LHC can measure the masses of the right-handed neutrinos and the right-handed leptonic mixing matrix, which could in turn be used to predict the rates for neutrinoless double decay and lepton flavor violating violating processes. The LR scale at the LHC energies offers great hope of observing these low energy processes in the present and upcoming experiments. © 2011 World Scientific Publishing Company.


Senjanovic G.,ICTP
Rivista del Nuovo Cimento | Year: 2011

The tiny neutrino masses and the associated large lepton mixings provide an interesting puzzle and a likely window to the physics beyond the standard model. This is certainly true if neutrinos are Majorana particles, since then, unlike in the Dirac case, the standard model is not a complete theory. The Majorana case leads to lepton number violation manifested through neutrinoless-double-beta decay and same-sign dileptons potentially accessible to colliders such as the LHC. This is covered at length. I discuss in these lectures possible theories of neutrino mass whose predictions are dictated by their structure only and this points strongly to grand unification. I cover in detail both SU(5) and SO(10) grand unified theories, and study the predictions of their minimal versions. The main message I wish to bring across is a serious hope of probing the origin of neutrino mass in near future, through the combined effort of high-energy collider and low-energy lepton number and lepton flavor violation experiments. © Società Italiana di Fisica.


Blau M.,University of Bern | Thompson G.,ICTP
Journal of High Energy Physics | Year: 2013

We study Chern-Simons theory on 3-manifolds M that are circle-bundles over 2-dimensional orbifolds Σ by the method of Abelianisation. This method, which completely sidesteps the issue of having to integrate over the moduli space of non-Abelian flat connections, reduces the complete partition function of the non-Abelian theory on M to a 2-dimensional Abelian theory on the orbifold Σ, which is easily evaluated. © 2013 SISSA, Trieste, Italy.

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