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
مدرسین: صدیقه سجادیان-فرهنگ حبیبی
۹-۷ دی ماه ۱۳۹۵ دانشکده فیزیک دانشگاه صنعتی شریف
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
علیرضا طالبیان اشکذری (دانشکده فیزیک دانشگاه تهران)
Abstract: We study the evolution of the “non-perturbative” metric perturbations in a Bianchi background in the long-wavelength limit. By applying the gradient expansion to the equations of motion we exhibit a generalized “Separate Universe” approach to the cosmological perturbation theory. Having found this consistent separate universe picture, we introduce the δM formalism for calculating the evolution of the tensor perturbations in anisotropic inflation models in almost similar way as the so-called δN formula for the superhorizon dynamics of the curvature perturbations. Likewise its ancestor, δN formalism, this new method can substantially reduce the amount of calculations related to the evolution of the tensor modes.
یکشنبه 14 آذر ماه 1395، ساعت 15:00
دانشکده فیزیک، تالار پرتوی
عاطفه جوادی (پژوهشکده نجوم پژوهشگاه دانش های بنیادی -IPM)
Abstract: The evolution of galaxies is driven by the birth and death of stars. Nearby galaxies in the Local Group offer us a complete suite of galactic environments that is perfect for studying the connection between stellar populations and galaxy evolution. Therefore, the Local Group of galaxies offers a superb near-field cosmology site. Here, we can reconstruct the formation histories, and probe the structure and dynamics, of spiral galaxies as well as the many dwarf satellite galaxies surrounding the Milky Way and Andromeda, and of isolated dwarfs using the resolved stellar populations. In this talk, first I will introduce a near-IR monitoring campaign of the Local Group spiral galaxy M33, carried out with the UK IR Telescope (UKIRT). The pulsating evolved stars are identified and their distributions are used to derive the star formation rate as a function of age. I will outline the methodology and will present the results for the central square kiloparsec and for the disc of M33. Then, I will introduce an ongoing survey (started in June 2015) to monitor the Local Group dwarf galaxies accessible from La Palma with Isaac Newton Telescope (INT). We will use the luminosity distribution of the LPVs to reconstruct the star formation history – a method we have successfully applied in other Local Group galaxies.
یکشنبه 7 آذر ماه 1395، ساعت 15:00
دانشکده فیزیک، تالار پرتوی
حلیمه میرآقایی (پژوهشکده نجوم پژوهشگاه دانش های بنیادی -IPM)
Abstract: Powerful radio galaxies display a very wide range of properties, both in their extended radio morphologies and in their optical spectra. We study the environment and host galaxy properties of radio galaxies with different radio morphologies from compact sources to very extended double lobed radio galaxies and with different optical spectra as high excitation (HERG; quasar-mode) and low excitation (LERG; jet-mode) radio galaxies in order to separate and distinguish the factors that drive the radio morphological variations from those responsible for the differences in spectral properties. We particularly compare i) compact sources with Fanaroff–Riley (FR) extended radio sources from the same class of excitation, ii) HERGs with the LERGs, iii) FR type I with the FR type II from the same class of excitation. We discuss the results and what causes the differences in each comparison.
یکشنبه 23 آبان ماه 1395، ساعت 15:00
دانشکده فیزیک، تالار پرتوی