28 SEP 2021
18:30 - 21:00

In this talk I will discuss a work in progress in which, together with Sho Tanimoto and Yuri Tschinkel, we study the distribution of rational points on some anisotropic spherical varieties of rank 1 over an arbitrary number field. Our work is the non-split analogue of the results of Valentin Blomer, Jorg Brudern, Ulrich Derenthal, and Giuliano Gagliardi where they consider split spherical varieties of rank 1 over the rational numbers, though our methods are completely different. In our proof we use the theory of automorphic forms, especially Waldspurger's celebrated theorem on toric periods, to analyse the height zeta function. Once this analysis is done, the result on the distribution of rational points follows from a standard Tauberian theorem. We hope to address split spherical varieties of rank 1 over an arbitrary number field using similar methods in a future work.
Zoom link:
https://us06web.zoom.us/j/9086116889?pwd=WGRFOGZWZ1FOMXJrcWpJMWFqUFIvQT09
Meeting ID: 908 611 6889
Passcode: 362880

28 SEP 2021
17:00 - 18:00

Abstract: We illustrate scenarios in which Hawking radiation collected in finite regions of a reservoir provides temporary access to the interior of eternal black holes through transient entanglement "islands". Whether these islands appear and the amount of time for which they dominate - sometimes giving way to a thermalization transition - is controlled by the amount of radiation we probe. In the first scenario, two reservoirs are coupled to an eternal black hole. The second scenario involves two holographic quantum gravitating systems at different temperatures interacting through a Rindler-like reservoir, which acts as a heat engine maintaining thermal equilibrium. This situation describes two eternal black holes radiating into each other through a shared reservoir. We will also discuss the analogous effect in the evaporating AdS2 black hole.
Paper: https://arxiv.org/abs/2107.14746
( for participating in this event, please contact us: "particles@ipm.ir" )

29 SEP 2021
11:00 - 12:00

Abstract: In this talk, we will briefly review some of the measures of entanglement and holographic proposals for computing them. Then we will be focus on entanglement wedge cross-section (EWCS) and evaluate this holographic correlation measure in asymptotically AdS geometries which are dual to boundary excited states. We describe a perturbative analysis for calculating EWCS between the vacuum and other states in symmetric configurations and present some analytical results. Finally, we discuss how these results are consistent with the behavior of other correlation measures including the holographic mutual information.
arXiv:2105.12476


Indico: https://indico.particles.ipm.ir/indico/event/431
https://meet.google.com/zfx-datc-ocm

29 SEP 2021
13:30 - 15:00

Abstract
We have examined the star formation history (SFH) of Andromeda VII (And VII), the brightest and most massive dwarf spheroidal (dSph) satellite of the Andromeda galaxy (M31). Although M31 is surrounded by several dSph companions with old stellar populations and low metallicity, it has a metal-rich stellar halo with an age of 6–8 Gyr. This indicates that any evolutionary association between the stellar halo of M31 and its dSph system is frail. Therefore, the question is whether And VII (a high-metallicity dSph located ∼220 kpc from M31) can be associated with M31ʼs young, metal-rich halo. Here we perform the first reconstruction of the SFH of And VII employing long-period variable (LPV) stars. As the most evolved asymptotic giant branch and red supergiant stars, the birth mass of LPVs can be determined by connecting their near-infrared photometry to theoretical evolutionary tracks. We found 55 LPV candidates within two half-light radii, using multiepoch imaging with the Isaac Newton Telescope in the i and V bands. Based on their birth mass function, the star formation rate (SFR) of And VII was obtained as a function of cosmic time. The main epoch of star formation occurred; 6.2 Gyr ago with an SFR of 0.006 ± 0.002 Me yr−1. Over the past 6 Gyr, we find slow star formation, which continued until 500 Myr ago with an SFR ∼ 0.0005 ± 0.0002 Me yr−1.


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29 SEP 2021
14:00 - 15:00

Abstract:


Mathematical models of evolution have attracted considerable attention in recent years. The main ingredients of such models are "selection", "reproduction", and "mutation". Furthermore, population structure plays an important role in evolution. "Evolutionary Graph Theory" is a powerful tool to study the interplay between population structure and evolutionary dynamics.
In this talk, we try to give a brief review of this theory and then we mention to a number of recent results, among them is the effect of network topology on fixation time and fixation probability of mutants. Furthermore we propose a mean field approach to obtain the fixation time analytically for some network topologies.




Date: Wednesday, September 29, 2021

Time: 14:00-15:00

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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

30 SEP 2021
15:30 - 17:00

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

Abstract:


Modern multi-channel recording devices offer the opportunity to untangle the coordination mechanisms of neural activity at a mesoscopic level. However, this requires novel multivariate analysis techniques that link the high-dimensional data with biophysically realistic models of network activity. We develop a methodology to generalize the analysis of spike-field coupling (SFC) to the multi-channel setting, while allowing interpretability of such coupling based on neural field models of network activity. SFC characterizes the relation between the spiking activity of individual neurons and field activity, reflecting mesoscopic network dynamics, and typically measured by Local Field Potentials (LFP). Although SFC approaches have been extensively applied, they were focused on quantifying coupling one pair at a time (between one unit and one LFP channel), thereby remaining largely blind to the population-level interactions that generate them. As a consequence, the rich spatiotemporal patterns of spikes and LFPs remained largely under-exploited, despite the insights into the underlying circuit dynamics they may provide.



We introduce "Generalized Phase Locking Analysis (GPLA)" that summarizes the spike-field coupling from multi-channel data by three interpretable quantities: LFP and spike vectors represent the dominant spatial distribution and relative phase shifts of neuronal ensemble and field activity in the recorded structure, while the generalized Phase Locking Value quantifies the strength of the coupling between these patterns.



Furthermore, we demonstrate the capability and interpretability of GPLA with various simulated and experimental datasets. First, GPLA’s performance is superior to univariate measures in the presence of large amounts of noise. Next, the application of GPLA on simulations of hippocampal sharp-wave-ripples (SWR) reveals various characteristics of hippocampal circuitry (e.g. communication flow from CA3 to CA1 during the SWR) with minimal prior knowledge. Finally, combining neural field simulations and GPLA applied on Utah array data recorded from anesthetized macaque reveals synchronized clusters of sites/neurons. This global pattern of synchronization PFC supports long-range excitatory horizontal connections and strong local recurrent inhibition as a plausible connectivity scheme of the recorded structure (ventrolateral Prefrontal Cortex), that has been partially verified experimentally.



Lastly, we address one of the challenges of statistical analysis of parallel spike trains by taking a step beyond bootstrapping methods. We exploit novel statistical frameworks, namely the random matrix theory, and provide an analytical significance test. This is of paramount importance given the increasing dimensionality of modern recording techniques, such as Neuropixel, that need computationally efficient statistical tests.



In summary, with GPLA, we can quantify, characterize, and statistically assess the interactions between population spiking activity and mesoscopic network dynamics.






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