Jeremi Ochab, Jerzy Szwed, Katarzyna Oleś i współpracownicy; publikacja w PLOS ONE
Po 7 dniach odpoczynku po 10-dniowym okresie niedoboru snu, szybkość reakcji uczestników niewielkiego badania wróciła do normy, ale nie doszli oni do siebie w pełni pod względem żadnych innych miar funkcjonowania.
Wiadomo, że niedobór snu negatywnie wpływa na funkcjonowanie człowieka, ale nie jest jasne, ile czasu potrzeba, aby w pełni dojść do siebie po jego dłuższych okresach. Aby rzucić więcej światła na ten temat, przeprowadziliśmy badanie na zdrowych dorosłych, którzy przeszli 10 dni ograniczenia snu, a następnie 7 dni snu nieograniczonego. Uczestnicy spędzali badanie w swoim codziennym środowisku, nosząc na ręce czujniki monitorujące ich codzienne wzorce aktywności. Codziennie badano ich aktywność mózgową elektroencefalografem (EEG), nastrój i senność, oraz mierzono ich czas reakcji i poprawność odpowiedzi w wymagającym dużej uwagi zadaniu. Po tygodniu nienormowanego snu uczestnicy nie powrócili do stanu sprzed ograniczenia snu w większości miar. Obejmowały one kilka miar aktywności EEG, wzorce odpoczynku i aktywności uchwycone przez czujniki ruchu oraz poprawność wykonywania zadań. Tylko czasy reakcji wróciły do poziomu wyjściowego.
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Nick Manton, Katarzyna Oleś, Tomasz Romańczukiewicz oraz Andrzej Wereszczyński; publikacja w Physical Review Letters
Two collective coordinates capture the fractal dynamics of kink-antikink collisions.
In the recent paper published in Physical Review Letters we show that the complicated dynamics of kink-antikink collisions in φ4 field theory, in one space dimension, can be described using a simplified model. We truncate the field theory dynamics to the field configurations proposed by Sugiyama, which are simple superpositions of kinks and their oscillatory shape modes. Assuming reflection symmetry, just two coordinates parametrize the kink locations and shape mode amplitudes. One coordinate is a variant of the naive amplitude, chosen to avoid a singularity at zero kink-antikink separation. (This resolution of a long-standing technical difficulty with Sugiyama's scheme we published in 2020.) The truncated dynamics takes place on a smooth curved surface, with an explicit metric and potential that are derived from the field theory. In collisions at small velocity the kink and antikink annihilate, although slowly; at high velocity they bounce and escape. In between, there is fractal dependence on velocity, with annihilation intervals separated by nested intervals of multiple bounces. The initial data incorporates our observation that a non-zero shape mode amplitude accurately describes the Lorentz contraction of a moving kink. The truncated dynamics qualitatively reproduces the fractal pattern seen in the field theory simulations, despite ignoring radiation. These ideas should extend to solitons and localized structures in other field theories.
Arkadiusz Bochniak, Błażej Ruba, Jacek Wosiek, Adam Wyrzykowski; wyróżnienie w Journal Club for Condensed Matter Physics
Despite being less known, local bosonizations of fermionic systems exist in spatial dimensions higher than one.
Interestingly, the dual bosonic systems are subject to local constraints, as in theories with gauge freedom. These constraints effectively implement long distance exchange interactions. In this work we study in detail one such system, proposed a long time ago. Properties of the constraints are elaborated for two-dimensional, rectangular lattices of arbitrary sizes. For several small systems the constraints are solved analytically. It is checked that spectra of reduced spin hamiltonians agree with the original fermionic ones. The equivalence is extended to fermions in presence of background Wegner Z2 fields coupled to fermionic parity. This is illustrated by an explicit calculation for a particular configuration of Wegner's variables. Finally, a possible connection with the recently proposed web of dualities is discussed.
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Andrzej Wereszczyński; grant OPUS 20
OPUS 20 • "Geometryczne modele materii barionowej - od jąder atomowych do zderzeń gwiazd neutronowych" (2021-07-12 – 2024-07-11)
Although all phenomena of nuclear physics should, in principle, be describable by the fundamental theory of strong interactions, Quantum Chromodynamics (QCD), this is practically unfeasible owing to the complexity of nuclear systems (nuclei and nuclear matter). Instead, phenomenological models, usually based on nonrelativistic quantum mechanics, are employed for the modeling of nuclear properties, where the interactions introduced in these models are typically fitted to experimental data rather than derived from a more fundamental theory. It is the main aim of this project to bridge the gap between fundamental theory and nuclear phenomena by developing a QCD-based effective field theory (EFT) regarding the relevant physical fields (mesons and baryons) and applying it to a reliable and quantitatively precise calculation of nuclear properties at all scales.
The aim of the project is to identify the correct solitonic (Skyrme) EFT of the fundamental theory of strong interaction and provide a unified description of baryonic (nuclear) matter at all scales. The Skyrme model is an example of an EFT with the additional fascinating property that, while mesons are introduced as the fundamental degrees of freedom, baryons, nuclei and nuclear matter emerge as collective nonlinear excitations (topological solitons).
Identification of an EFT which covers baryonic phenomena on all scales is important not only from theoretical point of view (showing a possible road to the original quantum theory) or as a tool allowing for an explanation of the existing experimental data (e.g., excitation bands of nuclei, the maximal mass of neutron stars) but can be essential for identification of new phenomena e.g., possibly observed in neutron stars mergers (properties of ultra-dense nuclear matter or searching for imprints of generalized theories of gravity).
Kamil Korzekwa and Matteo Lostaglio; publikacja w Physical Review X
For the past three decades, scientists have been harnessing the quantum features of nature to challenge the best-known classical methods of computing, metrology, and cryptography. In all these cases, quantum superposition allows one to perform certain tasks faster, more precisely, or more securely.
For the past three decades, scientists have been harnessing the quantum features of nature to challenge the best-known classical methods of computing, metrology, and cryptography. In all these cases, quantum superposition allows one to perform certain tasks faster, more precisely, or more securely. In a recent paper published in Physical Review X, Kamil Korzekwa and Matteo Lostaglio report a novel quantum advantage that reduces the amount of memory and time needed to implement certain dynamical processes, such as thermodynamic cooling or information processing. In their work, they introduce a unifying framework to theoretically analyze memory and time costs from a mathematical, computational, and thermodynamical point of view, and apply it to study three distinct scenarios where quantum advantages arise. First, they show that there exist stochastic processes that cannot be simulated classically without memory but can be implemented “quantumly” in a memoryless fashion. Second, they prove that for processes that require memory even in the quantum regime, there is an improvement over classical computers in the number of times the memory must be accessed or in its size. Third, they demonstrate that memoryless quantum processes allow for much better control of the system’s state than their classical counterparts. Their findings show that quantum mechanics provides powerful models to simulate stochastic processes and pave the way to the investigation of practical advantages for quantum information processing.
• Patryk Mach, Andrzej Odrzywołek; publikacja w Physical Review Letters
How fast does a moving black hole accrete dark matter?
In a recent paper published in Physical Review Letters Patryk Mach and Andrzej Odrzywołek give the answer to this question. In their work dark matter is modelled as a Vlasov gas of collisionless particles, interacting gravitationally with the black hole. The answer turns out to be quite surprising---the accretion rate (the rate at which the matter falls into the black hole) depends both on the black hole velocity and the temperature of the dark matter. For hot dark matter the accretion rate grows with the black hole speed. The accretion rate of cold dark matter attains a minimum value at some finite black hole velocity. While the accretion of dark matter on black holes is presently rather inefficient (under reasonable assumptions on the black hole mass, its velocity, and the density of the dark matter medium), it could have led to a significant growth of black holes in early cosmological epochs.
Yi-Fu Cai, Chunshan Lin, Bo Wang, Sheng-Feng Yan; publikacja w Physical Review Letters
The hot big bang expansion of our universe was probably triggered by the cosmic epoch called “reheating” in which a scalar field oscillated about the minimum of potential and decayed into matter and radiation that we observed nowadays.
In a recent paper published in Physical Review Letters Chunshan Lin and his collaborators pointed out that for a large class of modified gravity theories, this cosmic epoch gives rise to a novel sound speed resonance phenomenon on the cosmological stochastic gravitational waves background. The primary signal of this phenomenon is a sharp peak on the stochastic gravitational waves spectrum, which may reach the sensitivity of present and forthcoming gravitational waves experiments. This mechanism provides a promising observational window to test modified gravity. It bridges gravitational wave astronomy with new physics beyond general relativity at high energy scales.