15 OCT 2024
14:00 - 15:00

Date and time

Tuesday, October 15th, 2024 (Mehr 24th, 1403), 2:00 pm (Tehran zone)



Place : Room D, Farmanieh Building


Abstract
In previous work, we introduced an effective brane-world model for de Sitter space-time with no explicit dependence on brane tension or bulk cosmological constant. In this model the 4D de Sitter space emerges on a brane near the horizon of a 5D black hole. In the current work, we study the effective gravity on the brane beyond the linear level, with an approximate Z2 symmetry assumption, up to a conformal factor, and find that the evolution of the effective cosmological constant on the brane depends on the flux of energy towards and away from the black hole in the bulk. In this setup the presence of the black hole horizon sets the initial condition for the brane's evolution and the brane approaches its null configuration with de Sitter length approximately equal to the 5D Planck's length, as soon as the horizon forms. During the last stages of collapse following this phase (or further flux of matter in the bulk after the horizon is formed), the effective de Sitter length on the brane increases due to the in-falling flux. This phase is tentatively the transition between a low-scale inflationary phase and a late dark energy phase. Also we observe that the increase in the de Sitter length is accompanied with a flux of energy entering the brane due to the jump in the bulk flux across the brane. Considering the initial state of the brane to be in the proper Planck's distance neighborhood of the horizon, the configuration which is below the horizon is Euclidean AdS. This can be interpreted as a boundary proposal for the resulting cosmology.

14 OCT 2024
11:00 - 12:00

Abstract:

Designers and engineers have many options to choose from when con- sidering how to join metals to non- metals for structural, electrical, and pack- aging applications. These options could include mechanical means of fastening such as screws, bolts, rivets and other fasteners, or an elevated-temperature means such as soldering or brazing. Metal-ceramic braz- ing, the topic of this article, is particularly useful for fabricating high-reliability devices such as those used in high-voltage applica- tions or requiring hermetically sealed joints. This article is intended to familiarize the designer with brazing methods commonly used to join metals to ceramics, discuss the advantages and disadvantages of each method, and show the relative tensile strengths obtained from samples fabricated using these methods.

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

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

9 OCT 2024
14:00 - 15:00

Optimal transport is the problem of moving a mass of objects from an initial mass distribution to a final mass distribution with minimum cost. The input to the problem is the initial and final distributions, as well as the distance metric or cost of transportation between each initial position and each final position. We should match points in the initial mass with points in the final mass so as to minimize the total cost. This problem was first proposed in the context of economics and recently in the context of machine learning to compare and transform probability distributions. I shall mainly talk about these applications.
If I have time, in the second part of the lecture, I will talk about a new method for computing transportations between distributions in high dimensions. This approach is different from previous works in that it does not assume that the distributions are given explicitly. Rather, it assumes that we can just query or sample the distribution (through what is often called an oracle in the computer science literature.) This allows the method to work for inputs that may be exponentially larger than explicitly given inputs. The simple main technique behind our method is to change the components in the initial vector point one by one and as little as possible, while making sure we attain the final distribution. Our method can be turned into a specific algorithm for some parameterized classes of distributions and distance metrics. For each class, our method only guarantees that the transportation cost is not worse than the optimal transport of a worst-case instance among that class up to a constant multiplicative factor. This work is related to previous work on computational concentration of measure, which appeared in the context of adversarial machine learning. The second part of this talk is joint work with Salman Beigi, Mohammad Mahmoody, and Amir Najafi and is work in progress.
Zoom room information:
https://us06web.zoom.us/j/85237260136?pwd=MFSZoKdmRXAjfaSaBzbf19lTaaKglf.1
Meeting ID: 852 3726 0136
Passcode: 362880
Venue: Niavaran, Lecture Hall 1

9 OCT 2024
11:00 - 12:00

Abstract:

The extraction of parton distribution functions (PDFs) and the strong coupling constant relies heavily on physical observables. Utilizing a variety of appropriate data significantly impacts proton PDFs. In this lecture I will first review the procedure for obtaining new PDF sets. Then, it will explain the constraints imposed by experimental data, such as W/Z boson production, Drell-Yan processes, and jet measurements, on various parton distributions. Finally, it will discuss how simulated data for future colliders can improve PDFs and the strong coupling constant.

Link to Join Virtually:
https://meet.google.com/bda-vsem-tuv

9 OCT 2024
13:30 - 15:00

I will talk about the model-building approach to describe the very early universe, which can address the several unresolved puzzles of the hot Big Bang Cosmology. The formation of topological defects as a result of phase transition is another promising phenomenon to probe the unseen universe. I will briefly describe the formation of topological defects and the emission of the Stochastic Gravitational-Wave Background (SGWB). One of the topological defects, Cosmic Strings, may have an imprint on the CMB. I will briefly talk about how we can see their footprints in the CMB and constrain the cosmic string tension. Recently, (International Pulsar Timing Arrays) IPTAs have found strong evidence for the SGWB. But the quest for the inverse problem is still there. I will discuss how we can address it.

8 OCT 2024
14:00 - 15:00

Date and time

Tuesday, October 8th, 2024 (Mehr 17th, 1403), 2:00 pm (Tehran zone)





Link

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



Abstract
The specific transformation used to define the Majorana fermions in the conventional seesaw mechanism, and customarily identified as "charge conjugation", is not supported by a consistent unitary operator and thus it leads to mathematical (operatorial) ambiguities. It also fails as a classical transformation law in a Lorentz invariant field theory. To distinguish it from the standard charge conjugation symmetry, it has been named pseudo C-symmetry. The problematic aspects of pseudo-C transformation are circumvented in the seesaw mechanism if one uses Pauli-Guersey (or Bogoliubov-type) transformations to convert the class of Majorana neutrinos defined in terms of Weyl fields only by CP, to another class defined in terms of chiral fermions, with proper C, P and CP properties. Open problems regarding the nature of neutrino masses and Weinberg's dimension 5 operator will also be discussed.

7 OCT 2024
16:00 - 18:00

Understanding the Taking Condition

7 OCT 2024
11:00 - 12:00

Abstract:

Thousands of person-years have been invested in searches for New Physics (NP), the majority of them motivated by theoretical considerations. Yet, no evidence of beyond the Standard Model (BSM) physics has been found. This suggests that model-agnostic searches might be an important key to explore NP, and help discover unexpected phenomena which can inspire future theoretical developments. A possible strategy for such searches is identifying asymmetries between data samples that are expected to be symmetric within theStandard Model (SM). We propose exploiting neural networks (NNs) to quickly fit and statistically test the differences between two samples. Our method is based on an earlier work, originally designed for inferring the deviations of an observed dataset from that of a much larger reference dataset. We present a symmetric formalism, generalizing the original one; avoiding fine-tuning of the NN parameters and any constraints on the relative sizes of the samples. Our formalism could be used to detect small symmetry violations, extending the discovery potential of current and future particle physics experiments.

Based on:
https://arxiv.org/abs/2401.09530

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

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

2 OCT 2024
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IRCHEP 1403
Iranian Conference on High Energy Physics
Deciphering the Universe Ciphers
School of Physics, IPM
September 30th-October 2nd, 2024 (9-11 Mehr,1403)