2 JUN 2025
16:00 - 18:00

Our Contribution to Others' Wrongdoing

2 JUN 2025
11:00 - 12:00

Abstract:

A search for resonances in top quark pair (ttˉ) production in final states with two charged leptons and multiple jets is presented. The analysis is based on proton-proton collision data collected by the CMS experiment at the CERN Large Hadron Collider (LHC) at a center-of-mass energy of TeVs=13 TeV, corresponding to an integrated luminosity of 138 fb−1. The study investigates the invariant mass distribution of the ttˉ system, along with two angular observables that provide direct sensitivity to the spin correlations between the top quark and antiquark. A significant excess of events is observed near the kinematic ttˉ threshold when compared to the expectations from nonresonant production as predicted by fixed-order perturbative quantum chromodynamics (pQCD). This observed enhancement is compatible with the production of a color-singlet pseudoscalar quasi-bound toponium state in the 1S0[1] configuration, as predicted by nonrelativistic quantum chromodynamics (NRQCD). Within the framework of a simplified model for 1S0[1] toponium, the cross section of the excess above the pQCD prediction is measured to be: pbσexcess=8.8−1.4+1.2 pb.

Based on:
https://arxiv.org/abs/2503.22382, https://arxiv.org/abs/2503.22382, https://arxiv.org/abs/2503.22382, https://arxiv.org/abs/2503.22382

Meeting Place:
Seminar Room, School of Particles and Accelerators, IPM

Link to Join Virtually:
https://www.skyroom.online/ch/ipm-particles/journal-club

28 MAY 2025
11:00 - 12:00

Abstract:

Singularities in Newton's gravitation, in general relativity (GR), in Coulomb's law, and elsewhere in classical physics, stem from two ill-conceived assumptions: a) there are point-like entities with finite masses, charges, etc., packed in zero volumes, and b) the non-quantum assumption that these point-likes can be assigned precise coordinates and momenta. In the case of GR, we argue that the classical energy-momentum tensor in Einstein's field equation is that of a collection of point particles and is prone to singularity. In compliance with Heisenberg's uncertainty principle, we suggest replacing each constituent of the gravitating matter with a suitable quantum mechanical equivalent, here a Klien-Gordon (KG) or a Yukawa-ameliorated version of it, YKG field. KG and YKG fields are spatially distributed entities. They do not end up in singular spacetime points nor predict singular blackholes. On the other hand, YKG waves reach infinity as 〖1/r e〗^(-(κ±ik)r). They create the Newtonian r^(-2) term as well as a non-Newtonian r^(-1) force. The latter can explain the observed flat rotation curves of spiral galaxies, and is interpretable as an alternative gravity, a dark matter scenario, etc. There are ample observational data on flat rotation curves of spiral galaxies, coded in the Tully-Fisher relation, to support our propositions.


Indico Link:
https://indico.hep.ipm.ir/e/h.sheikhahmadi1

Meeting Place:
Seminar Room, School of Particles and Accelerators, IPM

Link to Join Virtually:
https://www.skyroom.online/ch/ipm-particles/weekly-seminar

28 MAY 2025
14:00 - 15:00

Solid-state spin defects in 3D materials have shown remarkable capabilities in quantum sensing and information processing. While these materials are effective, the search for scalable alternatives is ongoing. Two-dimensional materials like hexagonal boron nitride (hBN) are emerging as promising candidates. The negatively charged boron vacancy (VB) in hBN exhibits exceptional room-temperature properties, positioning it as a compelling platform for scalable quantum technologies. This lecture explores recent advances in harnessing VB centers for quantum technologies, focusing on three interconnected pillars: spin control, strain-mediated coupling, and decoherence mitigation. First, we demonstrate efficient nuclear spin hyperpolarization using active spin driving and the Holstein-Primakoff transformation. This enables the initialization of large-scale quantum simulators from thermal spin baths. Second, we propose a strain-induced coupling scheme in hBN nanoribbons. This scheme demonstrates robust room-temperature entanglement and Dicke-Ising simulations. Finally, we investigate the decoherence dynamics of VB centers, focusing on the interplay between dipolar hyperfine interactions and spin-phonon coupling. Our findings provide a foundation for developing practical quantum devices that leverage the advantages of van der Waals materials.


Venue: Room D, 3rd Floor, Farmanieh Building, IPM
Link: https://vmeeting2.ipm.ir/b/nan-gkn-wmh-exh

28 MAY 2025
14:00 - 15:00

In this talk, I will try to sketch the big picture of our universe's history (of course as far as we know till now). This leads us to the darkness, dark matter and dark energy, the standard model of cosmology. Then I will review very briefly the recent tensions and anomalies in this model. If we had time, I would like to end with my own question: Why is our universe so simple?



This Seminar is free, hybrid, and open to the public.

28 MAY 2025
17:30 - 19:00

In this talk we study some properties of the Hadamard products of symbolic powers, in particular, if for points $P, Qin {mathbb{P}}^2$, we get $I(P)^m*I(Q)^n= I(P*Q)^{m+n−1}$. We obtain different results according to the number of zero coordinates in $P$ and $Q$. Successively, we define the so called Hadamard fat grids, which are the result of the Hadamard product of two sets of collinear points with given multiplicites. The most important invariants of Hadamard fat grids, as minimal resolution, Waldschmidt constant and resurgence, are then computed using also tools and known results in ${mathbb{P}}^1 imes{mathbb{P}}^1$. (This is a joint work with I. Bahmani Jafarloo, C. Bocci, G. Malara).

Venue: online
https://zoom.us/join
Meeting ID: 9086116889
Passcode: 362880
Website: http://math.ipm.ac.ir/agnt/
Venue: , (Online)

28 MAY 2025
13:30 - 15:00

28 MAY 2025
14:00 - 15:00

In this talk we introduce the asymptotic almost sure expansion lower bounds of random d-regular graphs in the uniform model and provide improvements for d ≥ 4 through solving a parametrized relaxation of the expansion lower bound problem. As a concrete consequence of our main result, we prove that for large degrees d ≥ 6 � 10^4 the optimal a.a.s. expansion lower bound of d-regular graphs is greater than d/2‎ - ‎0.7942^{-} √d which is an improvement over the long-standing a.a.s. lower bound d/2‎ - ‎0.8326^{-} √d provided by B. Bollob�as (1988). Also, for small degrees, we apply our main result along with an a.a.s. upper bound of R. Lyons (2017) for bisection width to explicitly obtain improvements on known a.a.s. expansion lower bounds for small degrees 4 ≤ d ≤ 10. In particular, we report the lower bounds 0.4452 for d = 4, 0.7494 for d = 5 and 1.0584 for d = 6 that improve the best previously known results of A. Amit-N. Linial (2006).
These results are part of a joint collaboration with Dr. Amir Daneshgar.

Zoom room information:
https://us06web.zoom.us/j/84906984159?pwd=BCWaIbXBuku3A5I84zNg9mHFxVZjXD.1
Meeting ID: 849 0698 4159
Passcode: 362880
Venue: Niavaran, Lecture Hall 2

27 MAY 2025
14:00 - 15:00

Date and time

Tuesday, May 27th, 2025 (Khordad 6st, 1404), 2:00 pm (Tehran zone)



Link

https://www.skyroom.online/ch/schoolofphysics/highenergyseminar


Abstract
Fractons, characterized by restricted mobility and governed by higher-moment conservation laws, represent a novel phase of matter with profound connections to tensor gauge theories and emergent gravity. I will systematically explore the duality between fractons and non-Lorentzian particles—specifically, Carroll and Galilean particles—within electromagnetic (EM) fields. By constructing canonical actions for fractons in rank-2 gauge fields, we derive their equations of motion and demonstrate that static fractons exhibit duality with the electric sector of Carroll particles, while mobile fracton dipoles correspond to both the electric and magnetic sectors of Galilean particles. Furthermore, by gauging the fracton algebra, we develop a geometric framework for fracton gravity, linking it to non-Lorentzian spacetime geometries. These results unify fracton dynamics with the non-relativistic and ultra-relativistic limits of physics, offering insights into emergent gravity and exotic condensed matter systems.

27 MAY 2025
11:00 - 12:30

It has been believed that supermassive black holes (SMBHs) in most nearby galaxies are powered by hot accretion flows. Compared to the well-known standard thin disks (cold accretion mode), hot accretion flows exhibit significantly higher temperatures and faster radial velocities, resulting in much lower radiative efficiency. This talk presents global solutions of slowly rotating hot accretion flows onto SMBHs located at the centers of elliptical galaxies. The inflowing gas begins subsonically and becomes supersonic as it approaches the black hole, forming a transonic accretion flow. The hydrodynamic equations governing the system are solved numerically from the Bondi radius down to regions close to the event horizon. The focus is on slightly rotating accretion flows where radiative cooling is neglected. Special attention is given to the impact of outer boundary conditions—such as temperature and specific angular momentum—on the dynamics of the flow. The role of the host galaxy’s gravitational potential in shaping the accretion structure is also examined. Finally, the influence of outflows on the dynamics of slowly rotating accretion flows is discussed.

21 MAY 2025
18:00 - 19:30

Date and time,


6-7:30pm, Wednesday 21 May 2025 (31 Ordibehesht 1404)


Venue: Online



Link

https://www.skyroom.online/ch/schoolofphysics/colloquium



Abstract


I will argue that the usual effective field theory techniques break down in the rapdily expanding background of the early universe. The TCC ("Trans-Planckian Censorship Criterion") plays a key role in the argument. I will then discuss an attempt to obtain an emerging metric space-time and early universe cosmology starting from a quantum mechanical matrix model.

21 MAY 2025
12:30 - 13:30

Abstract:

In this lecture, I will discuss recent efforts on discovery of black holes. I will also explain and elaborate on cases in which I have contributed in these discoveries.

Poster:
https://particles.ipm.ac.ir/pdf/poster_drrahvar.pdf

Indico Link:
https://indico.hep.ipm.ir/e/s.rahvar

Meeting Place:
Seminar Room, School of Particles and Accelerators, IPM

Link to Join Virtually:
https://www.skyroom.online/ch/ipm-particles/special-seminar

21 MAY 2025
16:00 - 17:00

The emergence of AI, particularly large language models (LLMs), has dramatically reshaped the requirements for error-correcting codes, particularly in the realm of memory I/O during training. Massive data transfers involved in training LLMs necessitate extremely robust error correction to prevent costly retraining scenarios triggered by undetected errors (Silent Data Corruption). Traditional iterative decoding techniques are inadequate due to their latency constraints, pushing the field towards combinational logic implementations capable of achieving multiple-error correction under extremely tight latency budgets. Algebraic codes, which once seemed to have lost ground to iterative decoding algorithms, are experiencing a renaissance driven by these stringent AI-driven performance demands. By exploiting deep results from algebra, notably Galois theory, algebraic codes are now being implemented in fully combinational hardware circuits that offer both the necessary decoding speed and robust error-correction guarantees. This development underscores algebraic coding theory?s renewed relevance and critical importance for future high-performance AI systems​.

Subscribing the Mathematics Colloquium mailing list:
https://groups.google.com/g/ipm-math-colloquium
Venue: Niavaran, Lecture Hall 1

21 MAY 2025
13:30 - 15:00