Eventos-mais-informacao

Em 11-02-2014 / 14:00 /  IST, Alameda Campus, Physics Building, Physics Department Room,  2nd floor

Orador/Speaker: Peter Ring
Instituição/Institution: Physik-Department der Technischen / Universität München / Germany

Abstract:

So far, ab initio calculations in nuclear physics are restricted in several aspects, (i) they requirethree-body forces, (ii) they are limited to relatively light systems, and (iii) they neglect Lorentz invariance, a basic symmetry of the underlying QCD. Relativistic Brueckner-Hartree-Fock theory should, in principle, be able to bypass all these problems. In the past, however, it has only been used for the study of homogeneous infinite nuclear matter. Now this theory is applied for the first time for finite nuclear systems. Starting from a realistic bare nucleon-nucleon (NN) force adjusted to nuclear scattering data, the G-matrix is obtained as an effective interaction by solving the Bethe-Goldstone equation in an Harmonic oscillator basis. This G-matrix is inserted in a relativistic Hartree-Fock code for finite nuclei and in each step of the iteration a new G-matrix is calculated by solving the Bethe-Goldstone equation for the Pauli-operator derived from the corresponding Fermi surface in the finite system. The self-consistent solution of this iteration process allows to calculate ground state properties of finite nuclei without any adjustable parameters. No three-body forces are needed. First results are shown for doubly magic nuclei between 16O and 48Ca. Their ground state properties, such as binding energies or charge radii are largely improved as compared with the results obtained from non-relativistic Brueckner-Hartree-Fock theory. It is discussed that this theory provides a method to study also the ground state properties of heavy nuclei in ab initio calculations.

 

Mais informação/More information: Cláudia Romão, DF (+351) 218 419 142

Relativistic Brueckner-Hartree-Fock Theory for Finite Nuclei

Em 11-02-2014 / 14:00 /  IST, Alameda Campus, Physics Building, Physics Department Room,  2nd floor

Orador/Speaker: Peter Ring
Instituição/Institution: Physik-Department der Technischen / Universität München / Germany

Abstract:

So far, ab initio calculations in nuclear physics are restricted in several aspects, (i) they requirethree-body forces, (ii) they are limited to relatively light systems, and (iii) they neglect Lorentz invariance, a basic symmetry of the underlying QCD. Relativistic Brueckner-Hartree-Fock theory should, in principle, be able to bypass all these problems. In the past, however, it has only been used for the study of homogeneous infinite nuclear matter. Now this theory is applied for the first time for finite nuclear systems. Starting from a realistic bare nucleon-nucleon (NN) force adjusted to nuclear scattering data, the G-matrix is obtained as an effective interaction by solving the Bethe-Goldstone equation in an Harmonic oscillator basis. This G-matrix is inserted in a relativistic Hartree-Fock code for finite nuclei and in each step of the iteration a new G-matrix is calculated by solving the Bethe-Goldstone equation for the Pauli-operator derived from the corresponding Fermi surface in the finite system. The self-consistent solution of this iteration process allows to calculate ground state properties of finite nuclei without any adjustable parameters. No three-body forces are needed. First results are shown for doubly magic nuclei between 16O and 48Ca. Their ground state properties, such as binding energies or charge radii are largely improved as compared with the results obtained from non-relativistic Brueckner-Hartree-Fock theory. It is discussed that this theory provides a method to study also the ground state properties of heavy nuclei in ab initio calculations.

 

Mais informação/More information: Cláudia Romão, DF (+351) 218 419 142

CENTRA Seminar

Pushing the limits on primordial non-Gaussianity I: Radio Galaxies and the multi-tracer technique

Orador/Speaker: Luís Ferramacho
Instituição/Institution: CENTRA, IST
Resumo/Abstract:

I will present and discuss a method to constrain primordial non-Gaussianity models using radio-galaxies as tracers of halos of different mass and therefore, bias properties. More precisely, I will focus on radio-continuum surveys such as those planned for the Skare Kilometer Array (SKA) in its initial phase. Using simulated redshift distributions together with the expected evolution of bias for different galaxy populations (Star forming galaxies, Starbust galaxies, Radio-Quiet Quasars, FRI and FRII AGN galaxies), a Fisher matrix analysis was performed based on the predicted auto and cross angular power spectra for these galaxy populations. I will show that such multi-tracer technique can improve the information on non-Gaussianity by reducing the impact of cosmic variance on the constraints. The conclusion is that these surveys, even without delivering redshift information, have the potential to constrain non-Gaussianity to an accuracy 2 to 3 times better than the present contrain obtained with Planck CMB data, opening a window to obtain $\sigma_{f_{nl}}~1$ in the future, thus opening a window to probe inflationary physics.

 

Date: Thursday, February 27, 2014 – 14:30

Place: Physics Dept. Meeting Room, 2nd floor, IST

 

Próximo colóquio do DF: 'Magnetic Reconnection'

Orador/Speaker: Nuno Loureiro
Instituição/Institution: IPFN, IST
Resumo/Abstract:

A reconexão magnética é o processo de reconfiguração súbita da topologia de um campo magnético num plasma. É um fenómeno ubíquo em plasmas magnetizados, sendo responsável pelas explosões solares, tempestades geomagnéticas e disrupções e outras instabilidades em experiências de fusão por confinamento magnético, entre muitas outras aplicações.  A reconexão resulta de uma dinâmica multi-escala e multi-frequência extremamente complexa, convertendo de forma muito eficiente energia magnética em partículas altamente energéticas e aquecimento do plasma --- por exemplo, conjectura-se que múltiplos processos de reconexão magnética no Sol sejam a razão de a coroa solar ser cerca de 1000 vezes mais quente que a superfície.
Esta palestra revê progressos recentes na compreensão deste fascinante fenómeno, focando em particular uma possível explicação para o mistério que tem dominado esta área desde a década de 50: como justificar as rápidas taxas de reconexão que são comummente observadas.

Orador/Speaker: João Dias
Instituição/Institution: DEM, IST
Resumo/Abstract:

Local/Place: PA2,Ed. de Matemática,Piso -1, Campus da Alameda, IST

Data/Date:12 March, 16h30

A investigação e reconstituição de acidentes têm um papel muito importante para a determinação das causas e responsabilidade dos mesmos. Sendo um acidente um acontecimento muito rápido, as testemunhas não têm por vezes a perceção da forma como este ocorreu e as suas estimativas, por exemplo, em relação à velocidade não são fiáveis.  Muitas vezes os condutores mentem para fugirem às suas responsabilidades cíveis e criminais. 

A física e a matemática têm um papel fundamental na determinação das condições do acidente. Por exemplo, as leis da conservação da energia pode ser usadas para determinar a velocidade a partir de rastos de travagens, as leis da conservação do momento linear para determinar as direções e velocidade de veículos automóveis. Para acidentes mais complexos que envolvam utentes vulneráveis como peões ou motociclistas é necessário, por vezes, recorrer a formulações da dinâmica de corpos múltiplos como modelos detalhados de veículos e do corpo humano.

Nesta palestra, as equações da dinâmica de corpos múltiplos que são usadas na dinâmica de veículos e na biomecânica do impacto e da lesão são brevemente apresentadas e discutidas ilustrando-se a sua ligação com a física clássica. Exemplos de aplicação da reconstituição de acidentes reais ocorridos em Portugal, incluindo alguns acidentes mediáticos como o acidente com um autocarro na A23 em 2007 que teve 17 vitimas mortais.

Próximo colóquio do DF: Dynamics of Cortical Neuronal Populations

Orador/Speaker: Alfonso Renart
Instituição/Institution: Fund. Champalimaud
Resumo/Abstract:

 

O estudo da dinâmica dos circuitos locais no cortex cerebral é um dos assuntos mais fascinantes em neurociência. Um dos desafios neste campo é entender o modo como essa dinâmica  implementa as diversas computações envolvidas no processamento sensorial, na tomada de decisões ou na própria memória de trabalho. A nossa abordagem a este problema passa por gravar a actividade de um grande número de neurónios dos circuitos corticais, analisar esses dados, e tentar encontrar relações entre a atividade de neurónios diferentes para perceber como esses padrões de atividade são gerados, através de modelos matemáticos. Nesta palestra serão discutidos os métodos aplicados e como os mesmos contribuem para o avanço no conhecimento da amplificação sensorial dos circuitos corticais.

CFIF SEMINAR: Strangeness and causality constraint in heavy ion collision

Orador/Speaker: Paolo Castorina
Instituição/Institution: Physics and Astronomy Depart., Uni. Catania, Italy

Mais informação/More information: Cláudia Romão, DF (+351) 218 419 142

Próximo colóquio do DF: Weighing Einstein's messengers

Orador/Speaker: Richard Brito
Instituição/Institution: CENTRA, IST
Resumo/Abstract:

A teoria da Relatividade Geral de Einstein celebra o seu centésimo aniversário em 2015 como sendo uma das mais elegantes e bem sucedidas tentativas do ser humano em perceber as leis da física. No entanto algo tem de ceder. Existem actualmente fortes indícios de que 70% do nosso Universo é constituído por um tipo de energia desconhecida: a energia escura. Neste colóquio exploraremos uma nova e empolgante solucão para este problema, que consiste em promover a Relatividade Geral para uma teoria fundamental de gravitões com massa. Em particular mostraremos como é que poderemos usar buracos negros e ondas gravitacionais, para testar e distinguir estas teorias.

CFTP SEMINAR: Strangeness and causality constraint in heavy ion collision

Orador/Speaker: Paolo Castorina
Instituição/Institution: Physics and Astronomy Depart., Uni. Catania, Italy

Mais informação/More information: Cláudia Romão, DF (+351) 218 419 142

Resumo/Abstract:

The thermal multihadron production observed in different high energy collisions poses many basic problems: why do even elementary, e+ e-; and hadron-hadron, collisions show thermal behaviour? Why is there in such interactions a suppression of strange particle production? Why does the strangeness sup pression almost disappear in relativistic heavy ion collisions? Why in these collisions is the thermalization time less than ~ 0.5 fm/c? The recently proposed mechanism of thermal hadron production through Hawking-Unruh radiation can naturally answer the previous questions. Indeed, the interpretation of quark-antiquark pairs production, by the sequential string breaking, as tunneling through the event horizon of colour confinement leads to thermal behavior with a universal temperature, T ~ 170 Mev,related to the quark acceleration, a, by T = a/2?. The resulting temperature depends on the quark mass and then on the content of the produced hadrons, causing a deviation from full equilibrium and hence a suppression of strange particle production in elementary collisions. In nucleus-nucleus collisions, where the quark density is much bigger, one has to introduce an average temperature (acceleration) which dilutes the quark mass effect and the strangeness suppression almost disappears.

 

CENTRA Seminar: Some Magnetic Effects In The Sakai-Sugimoto Model

Orador/Speaker: Alfonso Ballon Bayona
Instituição/Institution: Universidade do Porto

Resumo/Abstract:
I will describe recent results concerning two magnetic effects in the Sakai-Sugimoto model. The Sakai-Sugimoto model is a String Theory model that provides a dual description of QCD-like theories in the large-N limit. The magnetic effects to be discussed are : i) Destruction of spiral phases at finite axial chemical potential, ii) Inhibition of confinement and chiral symmetry breaking at finite temperature.

 

Próximo Colóquio do DF: Numbers about Science and Higher Education in Portugal

Orador/Speaker: João Batista
Instituição/Institution: DGEEC-MEC

  Resumo/Abstract:

  Neste colóquio será apresentada uma síntese dos novos dados   estatísticos que estão a ser produzidos no Ministério da Educação e Ciência sobre o ensino superior. Nomeadamente, são analisados dados sobre taxas de desistência e transferência entre cursos, médias finais de curso, etc. Alguns dados relacionados com a Ciência em Portugal serão também analisados.



Próximo Colóquio do DF: Electricity from renewables in Portugal

   Oradores/Speakers:

    Reinhard Schwarz (DF-IST)

    Luís Bastos (SIEMENS S.A.)

    Aníbal Fernandes (ENEOP)

    Resumo/Abstract:Portugal ocupa    uma posição única no que respeita ao fornecimento de eletricidade proveniente de fontes de energia renovável. Neste colóquio serão abordados vários aspetos relacionados com a energia renovável no nosso país, com foco nas diferentes tecnologias de energia fotovoltáica (R. Schwarz, DFIST-IST), na produção de eletricidade a partir de energia eólica (A. Fernandes, ENEOP), e em projetos de infra-estruturas para energias renováveis (L. Bastos, SIEMENS S.A.). 




CENTRA-Seminar: Observable Signatures Of Loop Quantum Gravity In Black Hole Evaporation

Orador/Speaker: Jacobo Diaz-Polo

Instituição/Institution: Universidade do Minho (Braga)

Resumo/Abstract: Loop quantum gravity provides an effective description of quantum black holes that allows to reproduce the semi-classical Bekenstein-Hawking results for the entropy. In addition, quantum corrections also arise in this picture, remarkably, a discretization of the entropy in the Planck regime. I will present an overview of the framework and comment on the main features of the entropy computation. This will allow us to look deeper into the possible observational consequences of this setting. I will present some specific signatures that, should it be possible to record in an experiment the Hawking radiation from evaporating Planck-sized black holes, would provide an experimental test to this approach.

Mais informação/More information: Dulce Conceição, CENTRA (+351) 218 417 938

CFIF-Seminar: Polaritons as quantum fluids of light: dynamics and many-body effects

Orador/Speaker: Orador/Speaker: Hugo Terças
Instituição/Institution: Université Blaise Pascal - Clermont-Ferrand II

Resumo/Abstract:
Due to the strong coupling between photons and excitons in semiconductor microcavities, the non-linear interactions between the photons become sufficiently large to envisage collective effects. One of the main consequences is the formation of quantum fluids of light at relatively high temperatures. In this talk, I propose to discuss some aspects of the dynamics of Bose-Einstein condensates of polaritons and how they can be used to study physical phenomena typical from condensed matter. In particular, I will discuss the occurrence of dynamical instabilities and the formation of a Wigner crystal in a gas of dark half-solitons, the formation and transport of very light magnetic monopoles ("magnetricity"), and the engineering of artificial gauge fields for photons. To conclude, I will present some preliminary results on the exciton relaxation of polariton condensates.

Próximo Colóquio do DF: Dressing Mexican style: Hadrons, chiral symmetry and confinement

Orador/Speaker: Elmar Biernat

Instituição/Institution: CFTP-IST

Resumo/Abstract

As massas dos quarks de valência contribuem apenas com 2% da massa total do protão, sendo a grande maioria desta massa gerada por um efeito associado à interacção forte denominado por quebra de simetria quiral. Este fenómeno é então responsável pela maior parte da massa da matéria comum no Universo. Neste colóquio apresentar-se-ão as noções essenciais relativas ao mecanismo de quebra de simetria quiral através de um modelo simples e será discutida uma abordagem moderna à física hadrónica, que também apresenta esta característica.

CENTRA-Seminar: Understanding The Bi-universe

Orador/Speaker: Prado Martin-Moruno
Instituição/Institution: CENTRA, IST

RESUMO/ABSTRACT:
Unlike other theories of bimetric gravity, bigravity theories can be interpreted as describing two classical universes interacting only through gravity. In this framework I will present the “generalized Gordon ansatz”, an ansatz which greatly simplifies calculations in cosmological scenarios (and other situations of physical interest), and can be used to extract conclusions about the interplay of both gravitational sectors when considering the fulfillment of the null energy condition (NEC) by the effective stress energy tensors. In fact, I will show that in general situations the effective stress energy tensors associated to both gravitational sectors can only simultaneously satisfy the NEC when it is saturated. Nevertheless, this anti-correlation is only present for the pure gravitational degrees of freedom, and the occurrence of some extremality events (as bounces and singularities) in one universe would generically imply that they also take place in the other universe.

Próximo colóquio do DF: Quarkonium: a laboratory for strong interactions

Orador/Speaker: João Seixas

Instituição/Institution: Dep. Física - IST & LIP

Resumo/Abstract:

Das quatro interacções conhecidas a interacção forte é a que é responsável pela esmagadora maioria dos processos que ocorrem à nossa volta. Curiosamente é, simultâneamente, aquela que menos conhecemos. Neste colóquio mostraremos como os estados ligados entre um quark e um antiquark podem podem dar indicações preciosas sobre esta interacção tanto para a produção de partículas nas colisões entre protões até à formação de um estado desconfinado em que quarks e gluões formam um plasma.

CFIF-Seminar: Non-adiabatic dynamics of strongly paired fermions across a Feshbach resonance

Orador/Speaker: Maxim Dzero

Instituição/Institution: Kent State University and CFIF

Mais informação/More information: Cláudia Romão, DF (+351) 218 419 142

Resumo/Abstract: 
I will present a theory of far-from-equilibrium degenerate Fermi gas interacting through a diatomic Feshbach resonance. I will argue that a two-channel model adequately describes strongly interacting fermionic and bosonic (molecular) degrees of freedom. I will demonstrate how to employ integrability of the two-channel model to describe the limiting dynamics of the pairing amplitude as well as the steady state wave function for sudden changes of detuning frequency across the BCS-BEC crossover. In collisionless regime, on a time scale larger then the order parameter relaxation time condensate reaches a steady state. I will show that the following three steady states for an arbitrary strength of the perturbation emerge: (i) gapless steady state; (ii) steady state with constant value of the order parameter; (iii) steady state with the periodic order parameter and determine the asymptotic behavior of the order parameter in each of these regimes exactly.

CENTRA-Seminar: Quarks And Mesons In The Covariant Spectator Theory

Orador/Speaker: Elmar Biernat 

Instituição/Institution: IST-Lisbon

Resumo/Abstract:

98% of the proton mass is generated by a mechanism called dynamical chiral-symmetry breaking, making this strong-interaction effect responsible
for the bulk of the mass of ordinary matter in the Universe. I will introduce a modern approach to the description of hadrons that exhibits this feature and
present first results for the quark mass function and pion structure.


Mais informação/More information: Dulce Conceição, CENTRA (+351) 218 417 938

CENTRA-Seminar: Integrability and Inverse Scattering in Supergravity

Orador/Speaker: Amitabh Virmani

Instituição/Institution: Inst. of Physics, Bhubaneshwar

Resumo/Abstract:

STU supergravity becomes an integrable system for solutions that effectively only depend on two variables. This class of solutions includes the Kerr solution and its charged generalizations that have been studied in the literature. We present an inverse scattering method that allows to systematically construct solutions of this integrable system. The method is similar to the one of Belinski and Zakharov for pure gravity but uses a different linear system due to Breitenlohner and Maison and here requires some technical modifications. We illustrate this method by constructing a four-charge rotating solution from flat space. A generalization to other set-ups is also discussed.

Mais informação/More information: Dulce Conceição, CENTRA (+351) 218 417 938

CFIF-Seminar: Topological insulators driven by an electron spin

Orador/Speaker: Maxim Dzero

Instituição/Institution: Kent State University and CFIF

Mais informação/More information: Cláudia Romão, DF (+351) 218 419 142

Resumo/Abstract:

The application of ideas developed in topology to the electronic band structure led to an intriguing discovery: materials can conduct electricity at the surface while remaining insulating at the bulk. These materials, called topological insulators, will have transformative impact on spintronics, low-power transport, and quantum computing. The search for a true topological insulator took years because even best candidates exhibited significant bulk conductivity. Only recently, literally in the past few months, several experimental groups established that samarium hexaboride, discovered in 1969 in Bell Labs, is a first topological insulator in its bulk form. In my talk, I review the theory which paved the way for this discovery. I will explain how crystalline symmetry, electron-electron interactions, and orbital degeneracy contribute to protecting the topological states in SmB6. In addition, I will discuss the experimental signatures of metallic surface states. Finally, I formulate the theoretical principles for discovering new topological insulators with designable properties.


CENTRA-Seminar: Detection of B-mode polarization at degree angular scales using BICEP2

Orador/Speaker: Denis Barkats

Instituição/Institution: ESO-ALMA

Resumo/Abstract:

BICEP2 recently reported a detection of B-modes in the CMB polarization at degree angular scales. This B-mode pattern is widely interpreted as the likely signature from primordial gravitational waves, consistent with those predicted to arise in the first 10^-34 seconds of the history of the universe, stretched from quantum to classical scales by the exponential expansion of cosmic inflation. BICEP2 is a CMB polarimeter that was specifically designed to search for the elusive signal from inflationary gravitational waves in the B-mode power spectra around l = 80. BICEP2 has accumulated 3 years of data from the South Pole from 2010 to 2012, integrating continuously on a low-foreground region of effective size 1% of the whole sky. I will describe the experimental strategy, tests for foreground and systematics contamination, and results in the map and power spectra.

CENTRA-Seminar: Detection of B-mode polarization at degree angular scales using BICEP2

Orador/Speaker: Denis Barkats

Instituição/Institution: ESO-ALMA

Resumo/Abstract:

BICEP2 recently reported a detection of B-modes in the CMB polarization at degree angular scales. This B-mode pattern is widely interpreted as the likely signature from primordial gravitational waves, consistent with those predicted to arise in the first 10^-34 seconds of the history of the universe, stretched from quantum to classical scales by the exponential expansion of cosmic inflation. BICEP2 is a CMB polarimeter that was specifically designed to search for the elusive signal from inflationary gravitational waves in the B-mode power spectra around l = 80. BICEP2 has accumulated 3 years of data from the South Pole from 2010 to 2012, integrating continuously on a low-foreground region of effective size 1% of the whole sky. I will describe the experimental strategy, tests for foreground and systematics contamination, and results in the map and power spectra.

CENTRA-Seminar: SUBARU weak-lensing survey of dark matter sub halos in COMA cluster

Orador/Speaker: Toshifumi Futamase

Instituição/Institution: Tohoku Univ.

Resumo/Abstract:

 We present a 4 deg^2 weak lensing survey of Dark Matter subhalos in thevery nearby Coma cluster using the Subaru/Suprime-Cam. We have measured the mass of 32 subhalos detected in a model independent manner, down to the order of 10^-3 of the virial mass of the cluster. Weak lensing mass measurement of these shear selected subhalos enable us to investigate subhalo properties and the correlation between subhalos masses and galaxy luminosities for the first time. The subhalo mass function is well described by a single power law and the best-fit power index is 1.09^+0.42_-0.32 which agrees with the prediction by CDM paradigm. We also discuss possible future observation of DM subhalos using new instrument in Subaru telescope.

CFIF-Seminar: Origin of Matching Effect in Anti-dot Array of Superconducting NbN Thin Films

Orador/Speaker: Dr. Sangita Bose

Instituição/Institution: UM-DAE Center for Excellence in Basic Sciences, University of Mumbai, India

Resumo/Abstract:

We investigate the origin of matching effect in dis-ordered superconducting NbN thin films with periodic array of holes. Matching effects can arisedue to commensurate pinning (CP) where each hole traps an integer number of flux quanta. It can also originate from the Little Parks like Quantum interference Effect (QI) seen in an array of superconducting loops where the super-current around each loop goes to zero at integral number of flux quantum. QI therefore manifests as oscillations in true thermodynamic quantities with magnetic field and usually dominates close to the superconducting transition temperature (Tc). In our experiments, all dynamical quantities which can be influenced by the flux line motion under an external drive showed pronounced matching effects. However, the superconducting energy gap which is a true thermodynamic quantity did not show any periodic variation with magnetic fields for the same films. In addition the matching effect survived down to very low temperatures, as low as 0.09TC for the most dis-ordered film. Our results indicate that CP leading to vortex-vortex interaction is the dominant mechanism for the observed matching effects in these superconducting anti-dot films.

Mais informação/More information: Cláudia Romão, DF (+351) 218 419 142

CENTRA-Seminar: Exact and Perturbative Approaches to Gravitational Collapse with Rotation

Orador/Speaker: Jorge Rocha

Instituição/Institution: CENTRA-IST

Resumo/Abstract:
The study of gravitational collapse is a subject of great importance, both from an astrophysical and holographic point of view. In this respect, exact solutions can be very helpful but such known solutions are very scarce, especially when considering dynamical processes with rotation. I will identify a setup in which gravitational collapse of rotating matter shells can be addressed with analytic tools, at the expense of going to higher dimensions and considering equal angular momenta spacetimes. The framework for exact and perturbative studies is developed, relying on a thin shell approximation. I will also discuss applications of this machinery to the cosmic censorship conjecture and constructions of stationary solutions describing matter around rotating black holes.

Mais informação/More information: Dulce Conceição, CENTRA (+351) 218 417 938

CFTP SEMINAR: Eigenvector parametrisation, reactor mixing angle and hybrid seesaw

Orador/Speaker: Ivo de Medeiros Varzielas

Instituição/Institution: University of Basel, Switzerland

Resumo/Abstract:
It is useful to write the neutrino mass matrix in terms of the eigenvectors of the lepton mixing matrix. In terms of this decomposition, the neutrino mass matrix can be seen as originating from a tribimaximal dominant structure with small departures required by the reactor mixing angle. Such a structure arises very naturally in cases with more than one mechanism responsible for neutrino masses - "hybrid seesaw".

Mais informação/More information: Cláudia Romão, DF (+351) 218 419142

Próximo colóquio do DF: The Quantum Way of Doing Computations

Orador/Speaker: Prof. Rainer Blatt

Instituição/Institution: Institute for Experimental Physics, University of Innsbruck

Resumo/Abstract:
Since the mid-nineties of the 20th century it became apparent that one of the centuries’ most important technological inventions, computers in general and many of their applications could possibly be further enormously enhanced by using operations based on quantum physics. This is timely since the classical roadmaps for the development of computational devices, commonly known as Moore’s law, will cease to be applicable within the next decade due to the ever smaller sizes of the electronic components that soon will enter the quantum physics realm. Computations, whether they happen in our heads or with any computational device, always rely on real physical processes, which are data input, data representation in a memory, data manipulation using algorithms and finally, the data output. Building a quantum computer then requires the implementation of quantum bits (qubits) as storage sites for quantum information, quantum registers and quantum gates for data handling and processing and the development of quantum algorithms. In this talk, the basic functional principle of a quantum computer will be reviewed. It will be shown how strings of trapped ions can be used to build a quantum information processor and how basic computations can be performed using quantum techniques. In particular, the quantum way of doing computations will be illustrated by analog and digital quantum simulations and the basic scheme for quantum error correction will be introduced and discussed. Scaling-up the ion-trap quantum computer can be achieved with interfaces for ion-photon entanglement based on high-finesse optical cavities and cavity-QED protocols, which will be exemplified by recent experimental results.

CENTRA-Seminar: Universal Relations in Neutron Stars

Orador/Speaker: Dr. Leonardo Gualtieri

Instituição/Institution: University "La Sapienza" of Rome

Resumo/Abstract:
Neutron stars are "extreme" objects under many respects (density, gravitational field, rotation rate, etc.). Therefore, studying neutron stars we can probe still untested regimes of different fundamental interactions. While present astrophysical observation only measure the rotation rate and the mass of neutron stars, several other quantities could be measured by upcoming gravitational and X-ray detectors. However, even with those detectors, reaching a full understanding of neutron stars will not be an easy task. Indeed, each of the observables (such as the gravitational waveform, or the X-ray pulse profile) depends on several quantities, and in particular on the still elusive equation of state of nuclear matter. In addition, a violation of general relativity, if present, would probably be buried in the uncertainty associated with the equation of state. Recently discovered universal relations among some of the quantities characterizing neutron stars (in particular, the so-called I-Love-Q relations) can be a powerful tool to overcome these problems. PLACE: Physics Dept. Meeting Room, 2th floor, IST.

Próximo Colóquio do DF: Shrinking Country Size Particle Accelerators to Palm-Top Plasma-Based Devices

Orador/Speaker: Prof. Jorge Vieira

Instituição/Institution: GoLP/IPFN, Instituto Superior Técnico

Resumo/Abstract:
Particle accelerators are among the largest and most complex machines ever built. Future generations of more powerful accelerators are, however, limited by their large size and cost. Thus, to continuously boost accelerated particles energies, we will describe a promising advanced acceleration concept based on the use of plasmas. In connection with the most recent developments in the field, we will present full-scale, one-to-one computer simulation of recent experiments; address some of the challenges associated with successful experiments now being pursued at CERN and at SLAC; and explore outstanding questions for the future of this technology. Os aceleradores de partículas estão entre as maiores e mais complexas máquinas alguma vez construídas. Apesar do seu enorme sucesso, a tecnologia está no seu limite. Assim, para continuar a produzir feixes cada vez mais energéticos, iremos apresentar um dos mais avançados e promissores conceitos de aceleração propostos, baseado na utilização de plasmas. Em conexão com os avanços mais recentes neste campo, iremos mostrar resultados computacionais um-para-um de experiências recentes; explorar alguns dos desafios associados ao sucesso de experiências que irão realizar-se no CERN e no SLAC; e examinar questões críticas para o futuro da tecnologia.

CFIF-Seminar: Three component gyrotropic metamaterial

Orador/Speaker: Prof. Igor Tralle

Instituição/Institution: Faculty of Mathematics & Natural Sciences, University of Rzeszow, Rzeszow, Poland

Mais informação/More information: Cláudia Romão, DF (+351) 218 419 142

Resumo/Abstract:
We propose a comparatively simple way to fabricate a metamaterial which is both gyrotropic and of simultaneously negative permittivity and permeability. The idea is to make a mixture of three ingredients, where one of them would be responsible for the negativity of μ, while the other two would be responsible for the negativity of ε. The first component of the mixture is the ’swarm’ of single-domain ferromagnetic nano-particles, immersed in a mixture of other two, silver and mercury cadmium telluride.
>>> In the work we carried out computer simulations in the frame of proposed model in order to establish the domains of existence of such material searching through the vast parameter space. The main result of the paper can be summarized as follows. In the framework of the model, we succeeded in establishing the domains of gyromagnetic metamaterial existence, relative to all parameters characterizing the model, that is, temperature, external magnetic field, parameters of nano-particles, fraction of cadmium in Hg 1-xCdx Te - compound as well as the relative concentrations of the mixture components. Negative refraction and optical activity can be achieved only if the material is in external, however moderate magnetic field. On the other hand, in some circumstances it could be an advantage, since switching magnetic field on and off, one can trigger off left-handedness.

Próximo Colóquio do DF: The liberation of sound: music as an art-science

Orador/Speaker: João Marques Carrilho

Instituição/Institution: CITAR, Universidade Católica Portuguesa

Resumo/Abstract:
The human being is not only homo sapiens (rationality), but also homo demens (madness) and homo ludens (game), homo faber (productive action), homo economicus (interested only in personal profit), and so on. According to Edgar Morin, the over-specialization of knowledge is one of the great tragedies of the current Era. Reason appears nowadays restricted and fragmented, thus closed to the complexity of the Real. Creativity (or Imagination) is neither an exclusive property of Science nor of Art. In fact, it constitutes the ‘common ground’ from which any kind of knowledge or wisdom can flourish. The limits of the imagination are unpredictable. However, we should strive to be at the limits of our own knowledge, to be able to look behind the mirror, into the unknown. As Carl Jung said, "Fantasy is a fact. Fantasy is a form of energy, which has its own reality." It was this (apparently immaterial) energy that gave rise to the wheel, the airplane or the telescope. Electrons or DNA molecules are as real as the psychic world. Imagination is the living and invisible force that acts on "unrealized psychic energy" - a constant challenge to the (re) interpretation of the Real. Scientific and cultural contemporaneity affirms itself as the end of certainties, where the concept of Noise is the hallmark of deconstruction and polysemy, from the positive sciences to philosophy and art, permeating the postmodern situation of music. The electronic world has become a sensory extension of our perception, memory, and even imagination. Music as an art-science is a music which is at stake with the scientific knowledge of it’s own time. By studying to vibrations of a string, Pythagoras made the first physics a ‘musical physics’, which then integrated into a mystical vision of the world. Contrary to the generalized reductionism and technocracy, art music invites us to look for the infinity of thought and feeling, where all our cognitive functions are activated.

Mais informação/More information: Prof. Vitor Cardoso, DF (+351) 218 419 821

CENTRA-Seminar: Dynamics of Robertson-Walker spacetimes with diffusion

Orador/Speaker: Prof. Artur Alho

Instituição/Institution: CAMGSD - Instituto Superior Técnico

Resumo/Abstract:
We study the dynamics of spatially homogeneous and isotropic spacetimes containing a fluid undergoing microscopic velocity diffusion in a cosmological scalar field. After deriving a few exact solutions of the equations, we continue by analyzing the qualitative behavior of general solutions. To this purpose we recast the equations in the form of a two dimensional dynamical system and perform a global analysis of the flow. Among the admissible behaviors, we find solutions that are asymptotically de-Sitter both in the past and future time direction and which undergo accelerated expansion at all times.

Mais informação/More information: Dulce Conceição, CENTRA (+351) 218 417 938

CENTRA-Seminar: Holographic superconductors and the effect of back-reaction

Orador/Speaker: Betti Hartmann

Instituição/Institution: Jacobs University

Resumo/Abstract::
The AdS/CFT correspondence suggests that strongly coupled Conformal Field Theories (CFT) in d dimensions are dual to gravity theories in (d+1)-dimensional Anti-de Sitter (AdS) space-time and as such constitutes a realization of the holographic principle. The question remains whether this duality can be tested and verified. One suggestion is to use the correspondence to make predictions about the experimentally observed phenomenon of high-temperature superconductivity for which - up to now - no consistent microscopic theory in condensed matter physics exists. In this talk, I will mainly discuss holographic superconductors away from the probe limit, i.e. taking back-reaction of the space-time into account by solving the full set of coupled matter and gravity equations. I will demonstrate that this leads to some important changes in the qualitative and quantitative features as compared to the probe limit with a fixed space-time background.

 

Mais informação/More information: Dulce Conceição, CENTRA (+351) 218 417 938

CFTP-Seminar: The lepton flavor violation road to new physics

Orador/Speaker: Avelino Vicente

Instituição/Institution: Uni. Liège, Belgium

Resumo/Abstract:
The field of lepton flavor violation will live an era of unprecedented developments in the near future, with dedicated experiments in different fronts. The observation of a flavor violating process involving charged leptons would be a clear evidence of physics beyond the Standard Model, thus motivating the great effort in this direction. Furthermore, in case a positive signal is found, a proper theoretical understanding of the lepton flavor anatomy of a given model would become necessary. In this talk I will review the current situation, emphasizing the most relevant theoretical and phenomenological aspects of several processes. Then I will discuss two topics that have received some attention recently: lepton flavor violation in low-scale seesaw models and lepton flavor violating Higgs decays.

Mais informação/More information: Cláudia Romão, DF (+351) 218 419

Próximo Colóquio do DF: The watery past of Mars

Orador/Speaker: John Carter

Instituição/Institution: Institut d’Astrophysique Spatiale

Resumo/Abstract:
Recent orbital and landed missions to Mars have dramatically expanded our knowledge of the planet's early history. In particular, the identification of widespread and varied ancient water-bearing environments, concurrent with Earth's first oceans, opens the possibility for past habitability at Mars. A digest of exciting new results will be provided, as well as an overview of the investigation tools and planned missions.

Mais informação/More information: Prof. Vitor Cardoso, DF (+351) 218 419 821

Colóquio do DF: Radiation Protection in Medicine

Orador/Speaker: Pedro Vaz

Instituição/Institution: Centro de Ciências e Tecnologias Nucleares, IST

Resumo/Abstract: (+)

Mais informação/More information: Prof. Vitor Cardoso, DF (+351) 218 419 82

Quantum Computation and Information Seminar

"Exploring the interface between quantum physics and gravity in experiments"

Orador/Speaker: Markus Aspelmeyer, University of Vienna

Resumo/Abstract:
I will argue for and against possibilities to experimentally test the interface between quantum physics and gravity in a meaningful way. One promising route has been opened by massive mechanical objects that are now becoming available as new systems for quantum science. Devices currently under investigation cover a mass range of more than 17 orders of magnitude - from nanomechanical waveguides of some picogram to macroscopic, kilogram-weight mirrors of gravitational wave detectors. This provides access to a hitherto untested parameter regime of macroscopic quantum physics, eventually at the interface to gravity. My conclusion is therefore going to be an optimistic one.

Próximo Colóquio do DF: Black holes in the limit of very many dimensions

Orador/Speaker: Roberto Emparan

Instituição/Institution: ICREA, Barcelona

Resumo/Abstract:
Ninety-nine years after Einstein formulated General Relativity, the pivotal role of its most fundamental and fascinating objects --- the black holes --- is nowadays recognized in many areas of physics, even beyond astrophysics and cosmology. Still, solving the theory that governs their dynamics remains a formidable challenge that continues to demand innovative ideas. I will argue that, from many points of view, it is natural to consider the number of spacetime dimensions, D, as an adjustable parameter in the theory. Then we can use it for a perturbative expansion of the theory around the limit of very many dimensions, that is, considering 1/D as a small number. We will see that in this limit the gravitational field of a black hole simplifies greatly and its equations often turn out to be analytically tractable. A simple picture emerges in which, among other things, the shape of the black hole is determined by the same equations that describe soap bubbles.

Mais informação/More information: Prof. Vitor Cardoso, DF (+351) 218 419 821

Quantum Computation and Information Seminar

"Qubits in diamond: solid state quantum registers and nanoscale sensors"

Orador/Speaker: Fedor Jelezko, University of Ulm

Resumo/Abstract:
Recently, atom-like impurities in diamond (colour centers) have emerged as an exceptional system for quantum physics in solid state. In this talk I will discuss recent developments transforming quantum control tools into quantum technologies based on single colour centers. Specially, realization of quantum optical interface between spins and photons and scalable quantum registers in diamond will be presented. New applications of diamond qubits involving nanoscale magnetic resonance and force measurements will be shown. I will discuss single spin NMR paving the way to ultrasensitive MRI and structure determination of single biomolecules. The detection of proteins using nanodiamond sensors will be presented. I will also highlight future directions of research including combination of quantum error correction and sensing protocols and quantum enabled sensing and imaging in living cells.

Physics of Information Colloquium

"Quantum machine learning"

Orador/Speaker: Seth Lloyd, Massachusetts Institute of Technology

Resumo/Abstract:
Machine learning algorithms look for patterns in data. Frequently, that data comes in the form of large arrays of high-dimensional vectors. Quantum computers are adept at manipulating large arrays of high-dimensional vectors. This talk presents a series of quantum algorithms for big data analysis. The ability of quantum computers to perform Fourier transforms, find eigenvectors and eigenvalues, and invert matrices translates into quantum algorithms for clustering, principal component analysis, and for identifying topological features such as numbers of connected components, holes and voids. These quantum algorithms are exponentially faster than their classical counterparts: complex patterns in datasets of size N can be identified in time O(logN). The talk will discuss methods for implementing quantum machine learning algorithms on the current generation of quantum information processors.

Physics of Information Seminar

"Shining light on cortical connections"

Orador/Speaker: Leopoldo Petreanu (Champalimaud Neuroscience Programme)

Resumo/Abstract:
The cerebral neocortex underlies human's unique cognitive abilities. Understanding how the neuronal circuits of the neocortex allow so many complex behaviors is one of the central challenges of neuroscience. Functionally specialized cortical areas communicate with each others through an extensive network of long-range connections. We developed novel optical-methods that allow studying the connectivity and function of long-range cortical connections with unprecedented detail. Using these cutting-edge techniques we found rules organizing the connectivity of long-range projections linking distant cortical areas and we recorded the signals relayed by these projections in behaving mice.