25 NOV 2020
15:30 - 17:30

Some important C*-algebras have been recently flagged and studied as Fraisse limits. In the first part of my talk, I will review the Fraisse theory of C*-algebras (or more generally, of metric structures)--in the context of category theory (as opposed to model theory)--and give examples of approximately finite-dimensional non-commutative C*-algebras which appear as Fraisse limits and exabit Cantor-space-like universality/homogeneity properties. In the second part of my talk, I will show how one can apply the fact that a C*-algebra A is the Fraisse limit of a category of C*-algebras, which is sufficiently closed under taking tensor products of its objects and morphisms, to show that A is "self-absorbing" in a very "strong" sense (a C*-algebra is self-absorbing if it is isomorphic to its tensor product with itself). I will use this result to sketch a new and much easier proof for the notorious fact that the "Jiang-Su algebra" is strongly self-absorbing.
To join this webinar, please send an email to r.zoghi@gmail.com.

25 NOV 2020
11:00 - 12:00

Abstract: In my first talk, I review some basic concepts such as the early thermalization puzzle, hydrodynamization paradigm, and stability/casualty problem. I also speculate on a possible way to understand hydrodynamization in conformal theories. In my second talk, I present our results on the hydrodynamization in the first-order causal and stable(FOCS) hydrodynamics, with an emphasis on the differences between the FOCS and more traditional approaches.


https://journals.aps.org/prd/abstract/10.1103/PhysRevD.102.036022


https://www.skyroom.online/ch/ipm-particles/school-of-particles-and-accelerators-weekly-meeting


Indico: https://indico.particles.ipm.ir/indico/event/390

25 NOV 2020
13:30 - 15:00

We revisit the question of what mechanism is responsible for the spins of halos of dark matter. The answer to this question is of high importance for modeling galaxy intrinsic alignment, which can potentially contaminate current and future lensing data. In particular, we show that when the dark matter halos pass nearly by each other in dense environments-- namely halo assemblies-- they swing and spin each other via exerting mutual tidal torques. We show that this has a significant contribution to the spin of dark matter halos comparable to that of calculated by the so-called tidal torque theory (TTT). We use the results of state-of-the-art simulation of Illutris to check the prediction of this theory against the simulation data.
To join the seminar, please click on the following link

https://www.skyroom.online/ch/soa/weekly-seminar

Then click on the guest bottom to participate

25 NOV 2020
14:00 - 15:00

Abstract:

Thanks to magnetocrystalline anisotropy in van der Waals magnetic materials, the Mermin-Wagner restriction is deviated and two-dimensional (2D) magnetic materials had been discovered recently. The combination of magnetic and unique properties of 2D materials has been rapidly attracted the attention of researchers to novel magnetic 2D materials. So, the control of spin-spin interactions in magnetic systems is an essential topic related to the fundamental physics of quantum magnetism as well as applied spintronics-based technology. In this talk, the magnetic properties of monolayer CrI3, as a representative of 2D magnetic materials, are discussed. Density functional theory (DFT)-based calculations are used to extract a suitable spin model Hamiltonian that reproduces accurate and viable magnetic properties of monolayer CrI3. We present the mechanical strain and electric field dependence of various spin-spin interactions, consisting of symmetric isotropic exchange, magnetic anisotropy, and Dzyaloshinskii-Moriya (DM) interactions in the monolayer.


Date: Wednesday, November 25, 2020
Time: 14:00-15:00

To join the webinar, please follow this link:
https://www.skyroom.online/ch/schoolofphysics/condensed-matter-and-statistical-physics
and log in as guest.

Organized by: Condensed Matter and Statistical Physics Group, School of Physics (IPM)

Queries about this event should be addressed to Dr. A. Faridi at azadeh.faridi@ipm.ir

25 NOV 2020
19:30 - 21:30

Abstract: The discovery of the quark-gluon plasma that forms in heavy-ion collision experiments provides a unique opportunity to study the properties of matter under extreme conditions, as the quark-gluon plasma is the hottest, smallest, and densest fluid known to humanity. Studying the quark-gluon plasma also provides a window into the earliest moments of the universe, since microseconds after the Big Bang the universe was filled with matter in the form of the quark-gluon plasma. For more than two decades, the community has intensively studied the quark-gluon plasma with the help of a rich interaction between experiment, theory, phenomenology, and numerical simulations. From these investigations, a coherent picture has emerged, indicating that the quark-gluon plasma behaves essentially like a relativistic liquid with viscosity. More recently, state-of-the-art numerical relativity simulations strongly suggested that viscous and dissipative effects can also have non-negligible effects on gravitational waves produced by binary neutron star mergers. But despite the importance of viscous effects for the study of such systems, a robust and comprehensive theory of general relativistic fluids with viscosity is still lacking. This is due, in part, to difficulties to preserve causality upon the inclusion of viscous and dissipative effects into theories of relativistic fluids. In this talk, we will survey the history of the problem and report on a new approach to relativistic viscous fluids that paves the way for the systematic investigation of dissipative phenomena in general relativity.


https://us02web.zoom.us/meeting/register/tZ0pc--vrzwsHdz88USL3bZI6npJUwq166dH

23 NOV 2020
16:00 - 18:00

Fichte on Embodied Self-Consciousness

23 NOV 2020
11:00 - 12:00

Based on


https://journals.aps.org/prd/abstract/10.1103/PhysRevD.100.072002


Abstract: " Measurements of the top quark polarization and top quark pair spin correlations are presented using events containing two oppositely charged leptons produced in proton-proton collisions at a center-of-mass energy of 13 TeV. The data were recorded by the CMS experiment at the LHC in 2016 and correspond to an integrated luminosity of . A set of parton-level normalized differential cross sections, sensitive to each of the independent coefficients of the spin-dependent parts of the production density matrix, is measured for the first time at 13 TeV. The measured distributions and extracted coefficients are compared with standard model predictions from simulations at next-to-leading order (NLO) accuracy in quantum chromodynamics (QCD), and from NLO QCD calculations including electroweak corrections. All measurements are found to be consistent with the expectations of the standard model. The normalized differential cross sections are used in fits to constrain the anomalous chromo-magnetic and chromo-electric dipole moments of the top quark to and , respectively, at the 95% confidence level."



https://www.skyroom.online/ch/ipm-particles/journal-club-ep

19 NOV 2020
11:00 - 12:00

Abstract: There is a growing literature attempting to use holography to describe the equation of state (EoS) of deconfined quark matter to determine whether it can play a role in neutron star cores. Here we present a holographic model of QCD with a first order chiral restoration phase transition with chemical potential, µ. The first order behavior follows from allowing a discontinuity in the dual description as the quarks are integrated out below their constituent mass. The model predicts a deconfined yet massive quark phase at intermediate densities (350MeV< µ < 500MeV), above the nuclear density phase, which has a very stiff equation of state and a speed of sound close to one. We also include a holographic description of a colour superconducting condensate in the chirally restored vacuum and study the resulting EoS. By solving the Tolman-Oppenheimer-Volkoff equations with the resulting equations of state we find stable hybrid stars with quark cores. We compute the tidal deformability for these hybrid stars and show they are consistent with LIGO/Virgo data on a neutron star collision. Our holographic model shows that quark matter could be present at the core of such compact stars. Based on arXiv:2009.14079


https://www.skyroom.online/ch/ipm-particles/theory-weekly-seminar

19 NOV 2020
11:00 - 13:00

The almost Gorenstein property appeared in the work of Barucci and Fr�oberg in the context of 1-dimensional analytical unramified rings. It was extended to 1- dimensional local rings by Goto, Matsuoka and Thi Phuong, and later on to rings of higher dimension by Goto, Takahashi and Taniguchi. Let R be a positively graded Cohen-Macaulay K-algebra with canonical module ωR. We let a = − min{k ∈ Z : (ωR)k 6= 0}, which is also known as the a-invariant of R. R is called (graded) almost Gorenstein if there exists an exact sequence of graded R-modules 0 → R → ωR(−a) → E → 0, where E is an Ulrich module. Let H ⊂ N d be a normal affine semigroup, R = K[H] its semigroup ring over the field K and ωR its canonical module. The Ulrich elements for H are those h in H such that for the multiplication map by x h from R into ωR, the cokernel is an Ulrich module. In this talk, we provide some algebraic criterion for testing the Ulrich property. This is based on a joint work with J�urgen Herzog and Dumitru I. Stamate.
To join the meeting, go to the following link:
https://vmeeting.ipm.ir/b/mat-9px-g3c

18 NOV 2020
11:00 - 12:00

Abstract: In my first talk, I review some basic concepts such as the early thermalization puzzle, hydrodynamization paradigm, and stability/casualty problem. I also speculate on a possible way to understand hydrodynamization in conformal theories. In my second talk, I present our results on the hydrodynamization in the first-order causal and stable(FOCS) hydrodynamics, with an emphasis on the differences between the FOCS and more traditional approaches.


https://journals.aps.org/prd/abstract/10.1103/PhysRevD.102.036022


https://www.skyroom.online/ch/ipm-particles/school-of-particles-and-accelerators-weekly-meeting


Indico: https://indico.particles.ipm.ir/indico/event/389

18 NOV 2020
16:30 - 18:00

Organized by: School of Cognitive Sciences
to receive the link to join online, please send email to theoretical.neurosci.ipm@gmail.com

Abstract:


In sensory cortices, information about external stimuli is conveyed by collective neural activities. Small neural populations often express perceptual sensitivity of psychophysical observers, suggesting that stimulus properties are redundantly coded by correlated neurons. This implies the existence of 'information-limiting' structures in noise correlations, which limit information as the population size increases. However, the existence of such correlations and their underlying mechanisms in cortical activities are yet largely unexplored. Information conveyed by neural activities can be signified as the linear Fisher information that quantifies the sensitivity of population firing to stimulus changes. Here, by studying the statistics of eigenvalues of the covariance matrix we present a generalized view of the effect of noise correlations on linear Fisher information. This generalizes the so-called differential correlations [Morino-Bote, et al. Nat Neurosci 17, 1410–1417 (2014)] that were originally suggested as an exclusive form of the information-limiting correlations. By studying the role of correlations in the monkey V1 area, we then show that in small populations the correlations play a positive role in population coding. Despite the observed positive role, we present "evidence" for the existence of information limiting structures in activity of orientation-selective neurons in the monkey V1 area responding to drifting gratings [Kohn & Smith CRCNS.org]. Finally, despite recent reports [Rumyantsev, et al. Nature 580, 100–105 (2020).], we show how difficult it is to provide conclusive evidence to prove that information limiting structures exist in the brain.


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