У оквиру семинара Групе за гравитацију, честице и поља Института за физику у Београду, у петак, 20. маја 2022. године у 11:15 путем BigBlueButton платформе, др Марко Војиновић (Институт за физику у Београду), одржаће предавање:

A review of a few results at the interplay between quantum gravity and quantum information theory

САЖЕТАК:

I will give a review of two (if time permits maybe three) results obtained in collaboration with Nikola Paunkovic, on research at the intersection between quantum gravity (QG) and quantum information theory (QI). The first result deals with the possible space of states in an abstract QG formalism, and the restrictions imposed by gauge symmetry, specifically diffeomorphisms. It turns out that these restrictions generically rule out gravity-matter product states as gauge-noninvariant. The second result deals with the motion of a point-particle in QG, in particular in a background gravitational field constructed as a quantum superposition of two distinct spacetime geometries. The resulting trajectory of the particle fails to be described by a geodesic equation with respect to either geometry, giving rise to a correction term due to quantum interference between two geometries. We will discuss the consequences of this for the weak equivalence principle. Finally, we may briefly mention a few other recent results trending in the QI community, such as the quantum switch protocol, del Santo-Dakic protocol, and their relationship to QG.

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У оквиру семинара Нискофонске лабораторије за нуклеарну физику Института за физику у Београду, у понедељак, 23. маја 2022. године у 11 часова у Библиотеци Института за физику и путем Zoom платформе, др Игор Аникин (Богољубов лабораторија за теоријску физику, Обједињени институт за нуклеарна истраживања у Дубни), одржаће предавање:

Transverse-momentum dependent Distributions: Functional Complexity manifesting in Gluon Poles and Inverse Radon Transforms

САЖЕТАК:

As well-known, QCD can be applied to the description of hard reactions with the help of the factorization theorem.
The factorization theorem, as an extended method of asymptotical estimations, states that the short (hard) and long (soft) distance dynamics can be separated out provided the momentum transfer is large. In this connection, any types of parton distributions are stemming from the factorization procedure applied for a given hard process. In the talk, we discuss the functional complexity which is associated with the transverse momentum dependent parton distributions. Working with the semi-exclusive and inclusive reactions, we demonstrate the manifestation of complexity in the gluon pole contributions and in the inverse Radon transforms applied to the transverse momentum dependent generalized
parton distributions. The experimental observables which are directly probing the gluon poles have been suggested.

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Meeting ID: 914 2401 6765
Passcode: 110488

У оквиру семинара Центра за изучавање комплексних система Института за физику у Београду, у четвртак, 05. маја 2022. године у 14 часова путем Zoom платформе, др Предраг Поповић (Институт за физику Земље у Паризу), одржаће предавање:

Critical percolation threshold controls Arctic sea ice melt pond evolution

САЖЕТАК:

Arctic sea ice covers a vast area of nearly 15 million square kilometers at its peak annual extent. However, in recent years, it has been rapidly disappearing at a rate underestimated by most climate models. A likely reason for this underestimate are processes on scales smaller than tens of kilometers, which the large-scale models cannot resolve. One such small-scale process that contributes to the disappearance of the Arctic ice are meter-sized melt ponds that form on the ice’s surface during summer and absorb significant amounts of solar radiation. During the summer, these ponds evolve in a complicated manner that we do not yet fully understand. In this talk, we will show how the critical point of a connectivity transition – the percolation threshold – controls the melt pond evolution. The ponds evolve by draining through large holes that open over the summer on the ice’s surface so that above the percolation threshold, they can drain easily, while below the threshold, their drainage is impaired. In this way, the percolation threshold is an approximate upper bound on the pond coverage fraction. In fact, in a manner typical for critical phenomena, pond drainage is universal. This universality enables us to write an equation for their evolution below the threshold that compares well with field and satellite observations over most of the summer. Our work, thus, might help resolve some of the uncertainty present in the large-scale climate models and help better predict the fate of the Arctic ice.

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Meeting ID: 845 0021 3601
Passcode: 019682

У оквиру семинара Групе за гравитацију, честице и поља Института за физику у Београду, у петак, 29. априла 2022. године у 11 часова путем BigBlueButton платформе, Михаило Ђорђевић (Институт за физику у Београду), одржаће предавање:

Coleman-Mandula theorem

САЖЕТАК:

Coleman-Mandula theorem is a no-go theorem in theoretical physics. It states that space-time symmetries and internal symmetries cannot be combined in any but a trivial way. The main consequence of the theorem is impossibility of finding functional dependence between parameters of irreducible representations of the Poincare group (mass and spin), and parameters of irreducible representations of internal symmetry group (charge, color etc.). Finding a „loophole“ of the theorem would give a new insight into the relations between properties of elementary particles, and by doing that, it would also reduce the number of fundamental constants of the theory. In this seminar, we will give a precise formulation of the theorem, show its detailed proof based on very general physical assumptions and talk about possible ways of the generalization of the theorem and of „loopholing“ it.

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У оквиру дуплог семинара Центра за изучавање комплексних система Института за физику у Београду, у четвртак, 21. априла 2022. године у 14 часова путем Zoom платформе, др Марија Вранић (GoLP/Институт за плазму и нуклеарну фузију, Високи технички институт, Универзитет у Лисабону), одржаће предавање:

Sources of electrons, positrons, and gamma-rays from lasers within plasma channels

САЖЕТАК:

The recent rise in laser intensities accompanied by the ongoing construction of new laser facilities such as ELI, the Vulcan 10 PW, and APOLLON will place intensities above 10^23 W/cm^2 within reach. While propagating through a pre-formed plasma channel, a laser of such intensity allows for direct laser acceleration (DLA) of leptons in the radiation reaction dominated regime. The DLA scheme has already been demonstrated to provide high-charge electron beams (at a nC level) with moderate laser intensities  (10^20 W/cm^2). In this talk we will show what can be accomplished with near-future laser facilities. We find that increasing the laser power is bound to augment the charge content even further. The field structure formed due to electron beam loading allows for accelerating positrons. What is more, the interaction in the radiation dominated regime will provide a high flux of emitted photons, in hard x-ray and gamma-ray range. These photons can then be used as a seed for electron-positron pair creation, as well as a radiation source for applications.

Након тога др Томас Грисмајер (GoLP/Институт за плазму и нуклеарну фузију, Високи технички институт, Универзитет у Лисабону), одржаће предавање:

Electron-positron-photon cascades in ultrastrong electromagnetic fields

САЖЕТАК:

Electron-positron pair plasmas are tightly related to extreme astrophysical objects such as pulsar magnetospheres or gamma-ray bursts. Due to the inherent difficulties of studying these remote objects, it is desirable to study dense pair plasmas in the laboratory, both for fundamental purposes and astrophysical applications. The magnitude of the laser fields expected in the next generation of laboratories overlaps with the estimated fields of milliseconds pulsars. Producing pair plasmas in ultrastrong fields may demonstrate that we can mimic the conditions appropriate to these astrophysical environments in laboratories. The pair creation in such energy density environments is caused by the decay of gamma rays in intense fields. As pulsars efficiently convert the large-scale Poynting flux to gamma rays, the laboratory analog of a pulsar isexpected to efficiently convert optical laser light into gamma rays. This process usually leads to quantum electrodynamics (QED) cascades, as the pairs created re-emit hard photons that decay anew in pairs, eventually resulting in electron-positron-photon plasmas. In this talk we will present the QED cascades in the laboratory where the electromagnetic trap is comprised of colliding lasers, and in Pulsar magnetospheres.

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Meeting ID: 827 0093 8432
Passcode: 008340