Erik Verlinde
Delta-Institute for Theoretical Physics Institute of Physics, University of Amsterdam
Colloquium in Perimeter Institute – May 13, 2015
یکشنبه 17 بهمن 1395 ، ساعت 15:00
دانشکده فیزیک، طبقه 5 اتاق شورا
غزاله اصغری (دانشکده فیزیک دانشگاه صنعتی شریف)
Abstract: The word “quantization” is used both in physics and mathematics in many different senses. The common basis of all these theories is that the classical and quantum mechanics are just different realizations of the same abstract scheme. Geometric quantization goal is the construction of quantum objects using the geometry of the corresponding classical objects as a point of departure. The geometric quantization procedure falls into the following three steps: prequantization, polarization and metaplectic correction. Prequantization produces a natural Hilbert space together with a quantization procedure for observables that exactly transforms Poisson brackets on the classical side into commutators on the quantum side. Nevertheless, the prequantum Hilbert space is generally understood to be “too big”. The idea is that one should then select a Poisson commuting set of n-variables on the 2n-dimensional phase space and consider functions that depend only on these n variables. The n variables can be either real-valued, resulting in a position-style Hilbert space, or complex valued. A polarization is a coordinate independent description on such a choice of n Poisson-commuting functions. The metaplectic correction is a technical modification of the above procedure that is necessary in the case of real polarization and often convenient for complex polarization.
یکشنبه 10 بهمن ماه 1395، ساعت 15:00
دانشکده فیزیک، تالار پرتوی
محمد انصاری (دانشکده فیزیک دانشگاه صنعتی شریف)
Abstract: The inflationary models solve several problems of cosmology, such as horizon problem and the flatness of the Universe. But however there are lots of inflationary models which Cosmic Microwave Background (CMB) can’t rule out them now. Non-Gaussianity and tensor perturbation are two complementary probes for inflationary models. This is because the inflationary models have different predictions for these two observables, however they are not detected yet. The deviation of the scale invariance of the primordial power spectrum is another opportunity which is detected by CMB data but with low statistical significance. In this presentation I will talk about the last opportunity and justify how Large Scale Structure will help us to rule out more inflationary models or the inflation scenario itself (through some idea about clock signal models which is developed recently).
یکشنبه 3 بهمن ماه 1395، ساعت 15:00
دانشکده فیزیک، تالار پرتوی
Amir Aghamousa
Korea Astronomy and Space Science Institute, South Korea
Abstract: Strong gravitational lensing systems contain a wealth of information that can be used to estimate the expansion history of the universe. The light rays from different images of a source quasar experience different gravitational potentials and optical paths which result a time delay in the associated light curves. A reliable estimation of the time delay has crucial role in the process of expansion history estimation. In this talk we describe our proposed algorithm for time delay estimation which shows outstanding results in the Time Delay Challenge (TDC). This algorithm consists of the smoothing and cross-correlation methodologies as well as a quick way for error estimation. In continue we explain the modified version of this algorithm which recently we have developed. In this version we introduce a new time delay estimator which includes weighted cross-correlation and some other changes in the procedure of estimation. The modified algorithm shows more precise results on TDC simulated data. At the end we discuss the estimation of time delay related to the light curves of the lensed quasar SDSS J1001+5027 system and compare our results with the time delays obtained by different group of researchers for the same system.
یکشنبه 26 دی ماه 1395، ساعت 15:00
دانشکده فیزیک، تالار پرتوی
سمینار مشترک ذرات و کیهانشناسی
Amir Hossein Ghadimi
Laboratory of Photonics and Quantum Measurements
École Polytechnique Fédérale de Lausanne (EPFL)
یکشنبه 19 دی ماه 1395، ساعت 15:00
دانشکده فیزیک، تالار پرتوی
Roya Mohayaee
Institut d’Astrophysique de Paris
سه شنبه 14 دی ماه 1395، ساعت 15:00
دانشکده فیزیک، تالار پرتوی
The origin of the giant stream and phase structures in galaxies, in particular in M31
Roya Mohayaee
Institut d’Astrophysique de Paris
یکشنبه 12 دی ماه 1395، ساعت 15:00
دانشکده فیزیک، تالار پرتوی
انسیه عرفانی (دانشگاه تحصیلات تکمیلی علوم پایه زنجان)
Abstract: In this talk I will explain the possibility of primordial black holes (PBH) formation from particle production during inflation. We consider the scalar and the gauge quanta production in inflation models, where in the latter case, we focus in two sectors: inflaton coupled i) directly and ii) gravitationally to a U(1) gauge field. We do not assume any specific potential for the inflaton field. Hence, in the gauge production case, in a model independent way we show that the non-production of DM PBHs puts stronger upper bound on the particle production parameter. Our analysis show that this bound is more stringent than the bounds from the bispectrum and the tensor-to-scalar ratio derived by gauge production in these models. In the scenario where the inflaton field coupled to a scalar field, we put an upper bound on the amplitude of the generated scalar power spectrum by non-production of PBHs. As a by-product we also show that the required scalar power spectrum for PBHs formation is lower when the density perturbations are non-Gaussian in comparison to the Gaussian density perturbations.
یکشنبه 28 آذر ماه 1395، ساعت 15:00
دانشکده فیزیک، تالار پرتوی
زنگ پژوهش فوق العاده
Remo Ruffini
ICRANet, Pescara, Italy
Department of Physics and ICRA, University of Rome “La Sapienza”, Italy
Abstract: Our concept of Induced Gravitational Collapse (IGC paradigm) from an incipient Supernova into a companion Neutron Star, has unlocked the understanding of seven different families of GRBs, indicating the path for the formation of Black Holes in the Universe. An authentic laboratory of relativistic astrophysics has been unveiled in which new paradigms have been introduced in order to advance in the knowledge of the most energetic, distant and complex systems of our Universe. A novel paradigm of the Cosmic Matrix has been introduced which parallel, in a relativistic cosmic level, the concepts of an S Matrix introduced by Feynman, Wheeler and Heisenberg in the quantum world of microphysics. Here the “in” states are represented by a Neutron Star and a Supernova, the “out” states, generated, in less than a second, by a new Neutron Star and a Black Hole. This novel field of research needs very powerful technological observations in all wavelength ranging from Radio, to Optical, to X and Gamma radiation all the way to ultra-high-energy cosmic rays.
تالار دکتر جناب (آمفی تئاتر دانشکده فیزیک)
سه شنبه 1395/9/23
16:30-15:00
طیبه نادری (دانشکده فیزیک دانشگاه صنعتی شریف)
Abstract: We will consider what is perhaps the simplest model for the formation of non-linear (gravitationally bound) structures. Imagine that, we have a spherical region with density higher than the density of the background (which is equal to the critical density). According to general relativity, the evolution of this spherical overdensity will be independent of the background evolution, so that it will evolve exactly like a sub-universe with density higher than the critical density.
یکشنبه 21 آذر ماه 1395، ساعت 15:00
دانشکده فیزیک، تالار پرتوی