IST Austria: PubRep (Institute of Science and Technology)
Not a member yet
6140 research outputs found
Sort by
Chiral phonons
No full textA rapidly increasing body of work reporting phenomena associated with lattice vibrations carrying angular momentum has led to the emergence of the field of chiral phonons. Some of these properties, such as the phonon magnetic moment, also occur in achiral phonons that are circularly or elliptically polarized, while the presence of chirality has additional implications for the types of interaction allowed between the phonons and light, electrons and other quasiparticles. In this Perspective we introduce a framework for classifying phonons with angular momentum, and provide illustrations of the different types using examples from the recent literature. Specifically, we suggest the term ‘axial phonon’ to encompass all phonons that carry angular momentum, real or pseudo, and reserve the term ‘chiral phonon’ for those phonons that break improper rotational symmetry. We hope that this scheme provides clarification on the matter of phonon chirality and will serve as a guide for future research
ISTA Thesis
No full textVerifiable Delay Functions (VDFs) introduced by Boneh et al. (CRYPTO'18) are functions that require a prescribed number of sequential steps T to evaluate, yet their output can be verified in time much faster than T. Since their introduction, VDFs have gained a lot of attention due to their applications in blockchain protocols, randomness beacons, timestamping and deniability. This thesis explores the theory and applications of VDFs, focusing on enhancing their soundness, efficiency and practicality.
The only practical VDFs known to date are based on repeated squaring in hidden order groups. Consider the function VDF(x,T)=x^(2^T).
The iterated squaring assumption states that, for a random group element x, the result of VDF cannot be computed significantly faster than performing T sequential squarings if the group order is unknown. To make the result verifiable a prover can compute a proof of exponentiation (PoE) \pi. Given \pi, the output of VDF can be verified in time much less than T.
We first present new constructions of statistically sound proofs of exponentiation, which are an important building block in the construction of SNARKs (Succinct Non-Interactive Argument of Knowledge). Statistical soundness means that the proofs remain secure against computationally unbounded adversaries, in particular, it remains secure even when the group order is known. We thereby address limitations in previous PoE protocols which either required (non-standard) hardness assumptions or a lot of parallel repetitions. Our construction significantly reduces the proof size of statistically sound PoEs that allow for a structured exponent, which leads to better efficiency of SNARKs and other applications.
Secondly, we introduce improved batching techniques for PoEs, which allow multiple proofs to be aggregated and verified with minimal overhead. These protocols optimize communication and computation complexity in large-scale blockchain environments and enable scalable remote benchmarking of parallel computation resources.
We then construct VDFs with enhanced properties such as zero-knowledge and watermarkability. It was shown by Arun, Bonneau and Clark (ASIACRYPT'22) that these features enable new cryptographic primitives called short-lived proofs and signatures. The validity of such proofs and signatures expires after a predefined amount of time T, i.e., they are deniable after time T. Our constructions improve upon the constructions by Arun, Bonneau and Clark in several dimensions (faster forging times, arguably weaker assumptions).
Finally, we apply PoEs in the realm of primality testing, providing cryptographically sound proofs of non-primality for large Proth numbers. This work gives a surprising application of VDFs in the area of computational number theory.
Together, our contributions advance both the theoretical foundations and the real-world usability of VDFs in general and in particular of PoEs, making them more adaptable and secure for current and emerging cryptographic applications
ISTA Thesis
No full textThis thesis is organized into two parts, each comprising two chapters: Chapter 1 and 2 offer models for the evolution of vaccine resistance in response to diverse vaccination strategies. Chapter 3 and 4 review the statistics of records, their connection to models of innovation and an application to the cultural evolution of sports.
In chapter 1 we present a modelling study from 2021 on the evolution of SARS-CoV-2. At that time the vaccine-resistant Omicron variant had not yet evolved. In our model we consider a population that is becoming vaccinated over time, while a pathogen is spreading in the population and eventually becoming resistant to the vaccine. We explore effective pharmaceutical and non-pharmaceutical interventions to prevent the emergence of vaccine resistance.
In chapter 2 we model a particular set of complex vaccination strategies, mosaic and pyramid vaccination, where an immunologically diverse portfolio of vaccines is considered. We find that a bet-hatching strategy, in which vaccine types are distributed in the population, is effective at hindering the evolution of vaccine resistance if mutation rates are high.
In chapter 3 we switch gears and present a review on the statistics of records. We highlight similarities and analogies to other models in the fields of statistical physics, evolution and innovation. This offers interesting complimentary perspectives on well-known models.
In chapter 4 we apply models of record statistics and innovation to study cultural evolution in sport. We propose a model of sport evolution that combines deterministic improvements in performance and stochastic bursts of improvements due to innovation
Motivic counting of rational curves with tangency conditions via universal torsors
No full textUsing the formalism of Cox rings and universal torsors, we prove a decomposition of the Grothendieck motive of the moduli space of morphisms from an arbitrary smooth projective curve to a Mori Dream Space (MDS).
For the simplest cases of MDS, that of toric varieties, we use this decomposition to prove an instance of the motivic Batyrev--Manin--Peyre principle for curves satisfying tangency conditions with respect to the boundary divisors, often called Campana curves
Tracing star formation across cosmic time at tens of parsec-scales in the lensing cluster field Abell 2744
No full textWe present a sample of 1956 individual stellar clumps at redshift 0.7 < z < 10, detected with JWST/NIRCam in 476 galaxies lensed by the galaxy cluster Abell2744. The lensed clumps present magnifications ranging between μ = 1.8 and μ = 300. We perform simultaneous size-photometry estimates in 20 JWST/NIRCam median and broad-band filters from 0.7 to 5 μm.
Spectral energy distribution (SED) fitting analyses enable us to recover the physical properties of the clumps. The majority of the clumps are spatially resolved and have effective radii in the range Reff = 10–700 pc. We restrict this first study to the 1751 post-reionization era clumps with redshift 3, reflecting the rapid increase towards the peak of the cosmic star formation history. We conclude that the results achieved over the studied redshift range are in agreement with expectation of in situ clump formation scenario from large-scale disc fragmentation
The MUSE eXtremely Deep Field: Classifying the spectral shapes of Ly α -emitting galaxies
No full textContext. The hydrogen Lyman-alpha (Lyα) line, the brightest rest-frame ultraviolet line of high-redshift galaxies, exhibits a large variety of shapes, which is due to factors at different scales, from the interstellar medium to the intergalactic medium (IGM).
Aims. The aim of this work is to provide a systematic inventory and classification of the spectral shapes of Lyα emission lines to better understand the general population of high-redshift Lyα emitting galaxies (LAEs).
Methods. Using the unprecedentedly deep data from the MUSE eXtremely Deep Field (MXDF; up to 140 hour exposure time), we selected 477 galaxies observed in the ∼2.8−6.6 redshift range, 15 of which have a systemic redshift from nebular lines. We developed a method to classify Lyα emission lines in four spectral and three spatial categories by combining a pure spectral analysis with a narrow-band image analysis. We measured spectral properties, such as the peak separation and the blue-to-total flux ratio for the double-peaked galaxies.
Results. To ensure a robust sample for statistical analysis, we define two unbiased subsets, inclusive and restrictive, by applying thresholds for signal-to-noise ratio, peak separation, and Lyα luminosity, yielding a final unbiased sample of 206 galaxies. Our analysis reveals that between 32% and 51% of the galaxies exhibit double-peaked profiles, with peak separations ranging from 150 km s−1 to nearly 1600 km s−1. The fraction of double-peaked galaxies seems to evolve dependently with the Lyα luminosity, while we do not see a severe decrease in this fraction with redshift, which is expected given the IGM attenuation at high redshift. An artificial increase in the number of double-peaked galaxies at the highest redshifts may cause the observation of a plateau instead of a decrease. A notable number of these double-peaked profiles show blue-dominated spectra, suggesting unique gas dynamics and inflow characteristics in some high-redshift galaxies. The consequent fraction of blue-dominated spectra needs to be confirmed by obtaining new systemic redshift measurements. Among the double-peaked galaxies, 4% are spurious detections, that is, the blue and red peaks do not come from the same spatial location. Around 20% out of the 477 sources of the parent sample lie in a complex environment, meaning there are other clumps or galaxies at the same redshift within a distance of 30 kpc.
Conclusions. Our results suggest that the double-peaked LAE fraction may trace the evolution of IGM attenuation, but the faintest galaxies must be observed at high redshift. We also need more data to confirm the trend seen at low redshift. In addition, it is crucial to obtain secure systemic redshifts for LAEs to better constrain the nature of the Lyα double-peaked lines. Statistical samples of double-peaked and triple-peaked galaxies are a promising probe of the evolution of the physical properties of galaxies across cosmic time
Asymptotic series for low-energy excitations of the Fröhlich polaron at strong coupling
No full textWe consider the confined Fröhlich polaron and establish an asymptotic series for the low-energy eigenvalues in negative powers of the coupling constant. The coefficients of the series are derived through a two-fold perturbation approach, involving expansions around the electron Pekar minimizer and the excitations of the quantum field
BMP-dependent patterning of ectoderm tissue material properties modulates lateral mesendoderm cell migration during early zebrafish gastrulation
No full textCell migration is a fundamental process during embryonic development. Most studies in vivo have focused on the migration of cells using the extracellular matrix (ECM) as their substrate for migration. In contrast, much less is known about how cells migrate on other cells, as found in early embryos when the ECM has not yet formed. Here, we show that lateral mesendoderm (LME) cells in the early zebrafish gastrula use the ectoderm as their substrate for migration. We show that the lateral ectoderm is permissive for the animal-pole-directed migration of LME cells, while the ectoderm at the animal pole halts it. These differences in permissiveness depend on the lateral ectoderm being more cohesive than the animal ectoderm, a property controlled by bone morphogenetic protein (BMP) signaling within the ectoderm. Collectively, these findings identify ectoderm tissue cohesion as one critical factor in regulating LME migration during zebrafish gastrulation
Exchange anisotropies in microwave-driven singlet-triplet qubits
No full textThis .zip file contains the data to reproduce the figures and supplementary figures of "Exchange anisotropies in microwave-driven singlet-triplet qubits" by Jaime Saez-Mollejo et al
