3 DEC 2020
11:00 - 12:00

Abstract: We introduce the Einstein-Yang-Mills AdS black brane solution in the context of massive gravity. The ratio of shear viscosity to entropy density is calculated for this solution. This value violates the KSS bound if we apply the Dirichlet boundary and regularity on the horizon conditions.


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

2 DEC 2020
11:00 - 12:00

Abstract: High-luminosity fixed target experiments provide impressive sensitivity to new light weakly coupled degrees of freedom. In the first part of this talk, I will discuss the minimal case of a scalar singlet S coupled to the Standard Model through the Higgs portal, that decays visibly to leptons for scalar masses below the dipion threshold. The dataset from the LSND experiment is found to impose the leading constraints within two mass windows between mS ∼ 100 and 350 MeV. In the second part of the talk, I will introduce potentially the world's most sensitive location to search for millicharged particles in the 10 MeV to 100 GeV mass range: the forward region at the LHC. I will show that the proposed scintillator-based experiment, FORward MicrOcharge SeArch (FORMOSA) in this location, can discover millicharged particles in a large and unexplored parameter space, and study strongly interacting dark matter that cannot be detected by ground-based direct-detection experiments. Furthermore, I will discuss some additional physics potential of FORMOSA, that not only provides leading sensitivity to MCPs but also is extremely sensitive to other forms of exotica beyond the standard model (BSM), such as heavy neutrinos and DM with a large electric dipole moment (EDM).
arXiv:2004.14515
arXiv:2010.07941


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


Indico: https://indico.particles.ipm.ir/indico/event/392

2 DEC 2020
13:30 - 15:00

The analysis of Gravitational Waves (GW) data from the Advanced LIGO provides the mass of each companion of binary black holes as the source of GWs. The observations reveal that the mass of events corresponding to the binary black holes are much larger than the mass of astrophysical black holes. We suggest the Primordial Black Holes (PBHs) as the source of LIGO events. Assuming that 100% of the dark matter is made of PBHs, we estimate the rate at which these objects make binaries, merge and produce GWs as a function of redshift. The gravitational lensing of GWs by PBHs can also enhance the amplitude of the strain. We simulate GWs sourced by the binary PBHs, with the detection threshold of S/N>10 for both Livingston and Handford detectors. For the log-normal mass function of PBHs, we generate the expected distribution of events and compare our results with the observed events and find the best value of the mass function parameters (i.e Mc =25M⊙ and σ=0.6) in the lognormal mass function. Comparing the expected number of events with the number of observed ones reveals that even assuming all the dark matter is made of PBHs are not enough to produce the observed GW events and the astrophysical black holes should have the main contribution in the observed GW events.
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

2 DEC 2020
14:00 - 15:00

Interface Engineering of Magnetic Properties in Heavy-Metal/Ferromagnet Bilayer Devices

Abstract:

Spin-Orbit Interaction (SOI) is a relativistic effect that is central to describing magnetization dynamics in continuum limit where the focus is on the slow variation of magnetization order parameter. Magneto-Crystalline Anisotropy (MCA), intrinsic Gilbert damping and Dzyaloshinskii-Moriya Interaction (DMI) are some of the most important properties of ferromagnets (FMs) that are responsible for coupling to the crystallographic anisotropy, energy loss and noncollinear ground state spin texture, respectively. SOI can also be employed in conducting nonmagnetic (NM) materials to convert charge bias into spin current and vice versa. The generated spin current can be used to manipulate the magnetization orientation of an adjacent FM through Spin-Orbit Torque (SOT) mechanism. The efficiency of the charge to spin current conversion is often improved by employing materials with large spin-orbit coupling. In addition to SOT, the presence of a material with large SOI interfaced with the FM can also result in the introduction of interfacial MCA, Gilbert damping and DMI, all of which are inversely proportional to the thickness of the FM film. In this talk, I present my recent work on the first principles calculations of the effects of sawtooth shaped interface on Magneto-Crystalline Anisotropy (MCA), Spin-Orbit Torque (SOT) and Dzyaloshinskii-Moriya Interaction (DMI) in Heavy-metal(HM)/Ferromagnet(FM) bilayer devices. I show that the breaking of the inplane mirror symmetry due to a sawtooth shaped interface results in an effective reorientation of the Damping-Like (DL) SOT, reorientation of the easy axis and additional nonzero components for DMI tensor elements. The shape of the sawtooth interface can be controlled by the angle of the crystal growth direction, which provides a convenient approach to engineer the interfacial properties of the FM.

1 DEC 2020
14:00 - 15:00


Abstract:
Pseudo entropy is a generalization of entanglement entropy via post-selection. In this talk I will 1) review some properties of this generalization in holographic setups, where it was first introduced. 2) Show that pseudo entropy can be computed with the standard correlator method followed by an appropriate analytical continuation in free scalar field theories. 3) Introduce and discuss about its basic properties in free theories. 4) Show that in spin systems, it is an appropriate quantity to distinguish whether the two input states belong to the same / different phases of the model.

Date: Tuesday, 1 December
2 p.m. - 3 p.m. (Tehran time)

Zoom Link. (click)
Meeting ID: 864 3692 7670
Passcode: 096079

30 NOV 2020
11:00 - 12:00

Based on
https://arxiv.org/abs/2003.00099
https://arxiv.org/abs/1212.6869v2
https://arxiv.org/abs/0909.2460


Abstract: Once the existence of the Higgs boson is established at the CERN Large Hadron Collider (LHC), the focus will be shifted toward understanding its couplings to other particles. A crucial aspect is the measurement of the bottom Yukawa coupling, which is challenging at the LHC. In this paper we study the use of forward jet tagging as a means to secure the observation and to significantly improve the purity of the Higgs boson signal in the H to bbar decay mode from deep inelastic electron-proton scattering at the LHC. We demonstrate that the requirement of forward jet tagging in charged current events strongly enhances the signal-to-background ratio. The impact of a veto on additional partons is also discussed. Excellent response to hadronic shower and b-tagging capabilities are pivotal detector performance aspects.


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

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