Seminars



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Tue Oct 04, 2022 (1401/7/12)

       

Oct 04
1401/7/12

14:00
 

The effect of the interaction of dark matter and dark energy in galactic physics and the ISW effect

Abstract:Since most of the matter (energy) of the universe consists of dark matter and dark energy, it is not unlikely that there is even a weak interaction between the dark elements. In this presentation, we draw on the results of two previously performed simulations of cluster-sized haloes with self-interacting dark matter and present previous work on the density profile of galaxy clusters. describe completely. This density profile helps to find a velocity dispersion profile and the relation between cluster mass and density center. We consider two uses of galaxy clusters with these relations: the mass velocity dispersion and temperature relation. We also discuss the effect of this interaction on the profile of the mass function in the galactic halo and the ISW effect.
Lecturer(s): Javad Taghizadeh Firouzjaee
From : K.N. Toosi University of Technology
Research Group: HEPCO Group Weekly Seminar
More Info. : link

Tue Sep 20, 2022 (1401/6/29)

       

Sep 20
1401/6/29

14:00
 

Boundary Conditions of Warped AdS_3 in GMG

Abstract:In this talk, in the framework of general massive gravity, I am looking at the asymptotic symmetry, the solution space, and the global charges using the ACDS boundary conditions in the quadratic ensemble. We also show that the boundary counting of the degeneracy of states correctly reproduces the bulk thermodynamic entropy for WBTZ black holes.
Lecturer(s): Seyed Naseh Sajadi
From : School of Physics, IPM
Research Group: HEPCO Group Weekly Seminar
More Info. : link

Wed Apr 06, 2022 (1401/1/17)

       

Apr 06
1401/1/17

18:00
 

Uncovering Energetic Processes in the Interstellar/Intergalactic Medium with the Square Kilometre Array

Abstract:Investigating the physics and energetic of the medium where galactic structures, on various scales, are formed is the most fundamental step to understand the formation and evolution of galaxies. Modern galaxy evolution models suggest gas accretion from the intergalactic medium (IGM) or from cosmic filaments as a mechanism to maintain star formation and active galactic nucleus (AGN). Through gas heating and/or gas removal, these models also propose supernova feedback and AGN feedback as mechanisms to quench massive star formation. Observational studies, however, have not reached to a conclusive result showing that feedback can, in some cases, trigger star formation, leaving the issue as an open challenge. It seems that some basic concepts about the formation of structures in the interstellar medium (ISM) and the IGM are missed: What are physical parameters/agents governing the structure formation on various scales? How does the ISM/IGM energy balance change over cosmic time? The advent of the square kilometre array (SKA) and its instrumental capabilities tracing the most energetic ISM components has opened a new window shedding light on the issue. The SKA's sensitive radio continuum observations will trace high-energy particles and magnetic fields not only in star forming regions and AGNs, but also in more quiescent regions in molecular clouds and diffuse IGM, enabling us to study the role of magnetic fields/cosmic rays in structure formation. Sensitive radio continuum observations on large scales may also bring constrains on the entity of dark matter mapped by the Hubble Space Telescope (HST) and Dark Energy Camera (DECam).
Lecturer(s): Fatemeh Tabatabaei
From : IPM, School of Astronomy
Research Group: Physics Colloquium
More Info. : Link

Tue Mar 15, 2022 (1400/12/24)

       

Mar 15
1400/12/24

14:00
 

Amazing Neutrino Particles
Lecturer(s): Yasaman Farzan
From : School of Physics
Research Group: HEPCO Group Weekly Seminar
More Info. : link

Tue Mar 08, 2022 (1400/12/17)

       

Mar 08
1400/12/17

14:00
 

Stochastic Effects in inflationary cosmology

Abstract:In this talk, I will speak about the stochastic effects in inflationary cosmology. To this end firstly I will review the stochastic formalism and discuss the properties of the Wiener process in general. In the second part, I will review how the stochastic effects can emerge in inflationary cosmology and why studying these effects in the early universe cosmology is important. Finally, the applications of these effects in different models are discussed. In particular, I will speak about the stochastic effects in axion inflation and the formation of primordial black holes.
Lecturer(s): Amin Nassiri Raad
From : School of Astronomy, IPM
Research Group: HEPCO Group Weekly Seminar
More Info. : Link

Wed Mar 02, 2022 (1400/12/11)

       

Mar 02
1400/12/11

18:00
 

Dance of Cause and Effect: Fluctuation Induced Reduction of Dissipation in Classical Fluids

Abstract:About seventy years ago, G I Taylor noticed that the tails of two closely swimming spermatozoa, oscillate in a synchronized fashion as if both of them are controlled from one regulating center. The two sperms, on the other hand, has no mean of communication, but the viscous fluid in which they are swimming. To address the why question, behind the observation, he suggested the minimization of total dissipation in the viscous medium. Sixty years later, Taylors original idea was put to more detailed analytical investigations; non-intuitively, it failed to attribute the observed synchronization to the expected reduction of dissipation. We begin with a very different problem: (a) The motion of two passively trapped beads, which interact through hydrodynamic interactions, and face a driven flow. Both theoretically and experimentally we observe that they almost follow the very motion they would have, if they were to swim on their own in the opposite direction of the driven flow. Calling the phenomenon, the reverse dance, we successfully attribute it to the reduction of the total dissipation. We then (b) extend the minimalistic approach, to two sets of beads; each supposed to mimic the tail of one spermatozoon. Facing a driven flow, on top of their intrinsic oscillation, this is a minimalistic model to verify Taylors idea. The question is, does this simple model lead us to synchronization as well as reduction of fluids dissipation? And if so, can it explain why Taylors original model failed to correctly attribute synchronization with reduction of dissipation?
Lecturer(s): Seyyed Nader Rasuli
From : University of Guilan & School of Physics, IPM
Research Group: Physics Colloquium
More Info. : Link

Wed Mar 02, 2022 (1400/12/11)

       

Mar 02
1400/12/11

14:00
 

RGreen-X library: Exascale Green-Function-Based Methods

Abstract:A new open-source exascale library of Green-function-based methodologies is under developing. Its layered design will separate higher-level functionalities from architecture-dependent numerical routines, common to all code families. Considerations of scaling with system size favour the choice of algorithms based on real space sparseness and time-frequency transforms, like the real-space / imaginary-time approach (cubic scaling instead of the quartic scaling of other algorithms), whose larger amount of numerical evaluations as compared to data communication is also well suited for the massive parallelism in exascale machines. The new library, Green-X, will include time-frequency transformations, space transformations, sparse or full basis-set dependent transformations, and solutions of the Poisson equation.
Lecturer(s): Maryam Azizi
From : Universite Catholique de Louvain
Research Group: Condensed Matter and Statistical Physics Group Weekly Seminar
More Info. : Link

Tue Mar 01, 2022 (1400/12/10)

       

Mar 01
1400/12/10

18:00
 

The central dogma and entanglement in de Sitter space

Abstract:The central dogma of black hole physics -which says that from the outside a black hole can be described in terms of a quantum system with exp(Area/4G) states evolving unitarily - has recently been supported by computations indicating that the interior of the black hole is encoded in the Hawking radiation of the exterior. In this paper, we probe whether such a dogma for cosmological horizons has any support from similar computations. The fact that the de Sitter bifurcation surface is a minimax surface (instead of a maximin surface) causes problems with this interpretation when trying to import calculations analogous to the AdS case. This suggests anchoring extremal surfaces to the horizon itself, where we formulate a two-sided extremization prescription and find answers consistent with general expectations for a quantum theory of de Sitter space: vanishing total entropy, an entropy of A/4G when restricting to a single static patch, an entropy of a subregion of the horizon which grows with the region size and threatens the central dogma until an island-like transition at half the horizon size when the entanglement wedge becomes the entire static patch interior, and a de Sitter version of the Hartman-Maldacena transition.
Lecturer(s): Edgar Shaghoulian
From : University of Pennsylvania
Research Group: HEPCo Group Weekly Seminar
More Info. : Link

Wed Feb 23, 2022 (1400/12/4)

       

Feb 23
1400/12/4

14:00
 

Random Long-range interacting spin chains: Entanglement properties

Abstract:Quantum information theoretical measures are useful tools for characterizing quantum dynamical phases. However, employing them to study excited states of random spin systems is a challenging problem. Here, we report results for the entanglement entropy (EE) scaling of excited eigenstates of random XX antiferromagnetic spin chains with long-range (LR) interactions decaying as a power law with distance with exponent $\alpha$. To this end, we extend the real-space renormalization group technique for excited states (RSRG-X) to solve this problem with LR interaction. For comparison, we perform numerical exact diagonalization (ED) calculations. From the distribution of energy level spacings, as obtained by ED for up to $N\sim 18$ spins, we find indications of a delocalization transition at $\alpha_c \approx 1$ in the middle of the energy spectrum. With RSRG-X and ED, we show that for $\alpha>\alpha^*$ the entanglement entropy (EE) of excited eigenstates retains a logarithmic divergence similar to the one observed for the ground state of the same model, while for $\alpha<\alpha^*$ EE displays an algebraic growth with the subsystem size $l$, $S_l\sim l^{\beta}$, with $0<\beta<1$. We find that $\alpha^* \approx 1$ coincides with the delocalization transition $\alpha_c$ in the middle of the many-body spectrum. An interpretation of these results based on the structure of the RG rules is proposed, which is due to {\it rainbow} proliferation for very long-range interactions $\alpha\ll 1$. We also investigate the effective temperature dependence of the EE allowing us to study the half-chain entanglement entropy of eigenstates at different energy densities, where we find that the crossover in EE occurs at $\alpha^* < 1$.
Lecturer(s): Javad Vahedi
From : Jacobs University Bremen
Research Group: Condensed Matter and Statistical Physics Group Weekly Seminar
More Info. : Link

Tue Feb 22, 2022 (1400/12/3)

       

Feb 22
1400/12/3

14:00
 

Supertranslation-Invariant Dressed Lorentz Charges

Abstract:We present an explicit formula for Lorentz boosts and rotations that commute with BMS supertranslations in asymptotically flat spacetimes. Key to the construction is the use of infrared regularizations and of a unitary transformation that makes observables commute with soft degrees of freedom. We explicitly verify that our charges satisfy the Lorentz algebra and we check that they are consistent with expectations by evaluating them on the supertranslated Minkowski space and the supertranslated Kerr black hole.
Lecturer(s): Reza Javadinezhad
From : New York University
Research Group: HEPCo Group Weekly Seminar
More Info. : Link

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