Study Of Fundamental Interactions Research Articles

Optically Controlled Nano-Transducers Based on Cleaved Superlattices for Monitoring Gigahertz Surface Acoustic Vibrations.

Surface acoustic waves (SAWs) convey energy at subwavelength depths along surfaces. Using interdigital transducers (IDTs) and opto-acousto-optic transducers (OAOTs), researchers have harnessed coherent SAWs with nanosecond periods and micrometer localization depth for various applications. These applications include the sensing of small amount of materials deposited on surfaces, assessing surface roughness and defects, signal processing, light manipulation, charge carrier and exciton transportation, and the study of fundamental interactions with thermal phonons, photons, magnons, and more. However, the utilization of cutting-edge OAOTs produced through surface nanopatterning techniques has set the upper limit for coherent SAW frequencies below 100 GHz, constrained by factors such as the quality and pitch of the surface nanopattern, not to mention the electronic bandwidth limitations of the IDTs. In this context, unconventional optically controlled nanotransducers based on cleaved superlattices (SLs) are here presented as an alternative solution. To demonstrate their viability, we conducted proof-of-concept experiments using ultrafast lasers in a pump-probe configuration on SLs made of alternating AlxGa1-xAs and AlyGa1-yAs layers with approximately 70 nm periodicity and cleaved along their growth direction to produce a periodic nanostructured surface. The acoustic vibrations, generated and detected by laser beams incident on the cleaved surface, span a range from 40 to 70 GHz, corresponding to the generalized surface Rayleigh mode and bulk modes within the dispersion relation. This exploration shows that, in addition to SAWs, cleaved SLs offer the potential to observe surface-skimming longitudinal and transverse acoustic waves at GHz frequencies. This proof-of-concept demonstration below 100 GHz in nanoacoustics using such an unconventional platform might be useful for realizing sub-THz to THz coherent surface acoustic vibrations in the future, as SLs can be epitaxially grown with atomic-scale layer width and quality.

Isospin-Symmetry Breaking within the Nuclear Shell Model: Present Status and Developments

The paper reviews the recent progress in the description of isospin-symmetry breaking within the nuclear shell model and applications to actual problems related to the structure and decay of exotic neutron-deficient nuclei and nuclei along the N=Z line, where N is the neutron number and Z the atomic number. The review recalls the fundamentals of the isospin formalism for two-nucleon and many-nucleon systems, including quantum numbers, the spectrum’s structure and selection rules for weak and electromagnetic transitions; and at the end, summarizes experimental signatures of isospin-symmetry breaking effects, which motivated efforts towards the creation of a relevant theoretical framework to describe those phenomena. The main approaches to construct accurate isospin-nonconserving Hamiltonians within the shell model are briefly described and recent advances in the description of the structure and (isospin-forbidden) decay modes of neutron-deficient nuclei are highlighted. The paper reviews major implications of the developed theoretical tools to (i) the fundamental interaction studies on nuclear decays and (ii) the estimation of the rates of nuclear reactions that are important for nuclear astrophysics. The shell model is shown to be one of the most suitable approaches to describing isospin-symmetry breaking in nuclear states at low energies. Further efforts in extending and refining the description to larger model spaces, and in developing first-principle theories to deal with isospin-symmetry breaking in many-nucleon systems, seem to be indispensable steps towards our better understanding of nuclear properties in the precision era.

The Bulk van der Waals Layered Magnet CrSBr is a Quasi-1D Material.

Correlated quantum phenomena in one-dimensional (1D) systems that exhibit competing electronic and magnetic order are of strong interest for the study of fundamental interactions and excitations, such as Tomonaga-Luttinger liquids and topological orders and defects with properties completely different from the quasiparticles expected in their higher-dimensional counterparts. However, clean 1D electronic systems are difficult to realize experimentally, particularly for magnetically ordered systems. Here, we show that the van der Waals layered magnetic semiconductor CrSBr behaves like a quasi-1D material embedded in a magnetically ordered environment. The strong 1D electronic character originates from the Cr-S chains and the combination of weak interlayer hybridization and anisotropy in effective mass and dielectric screening, with an effective electron mass ratio of mXe/mYe ∼ 50. This extreme anisotropy experimentally manifests in strong electron-phonon and exciton-phonon interactions, a Peierls-like structural instability, and a Fano resonance from a van Hove singularity of similar strength to that of metallic carbon nanotubes. Moreover, because of the reduced dimensionality and interlayer coupling, CrSBr hosts spectrally narrow (1 meV) excitons of high binding energy and oscillator strength that inherit the 1D character. Overall, CrSBr is best understood as a stack of weakly hybridized monolayers and appears to be an experimentally attractive candidate for the study of exotic exciton and 1D-correlated many-body physics in the presence of magnetic order.

Microfluidic Microbial Bioelectrochemical Systems: An Integrated Investigation Platform for a More Fundamental Understanding of Electroactive Bacterial Biofilms.

It is the ambition of many researchers to finally be able to close in on the fundamental, coupled phenomena that occur during the formation and expression of electrocatalytic activity in electroactive biofilms. It is because of this desire to understand that bioelectrochemical systems (BESs) have been miniaturized into microBES by taking advantage of the worldwide development of microfluidics. Microfluidics tools applied to bioelectrochemistry permit even more fundamental studies of interactions and coupled phenomena occurring at the microscale, thanks, in particular, to the concomitant combination of electroanalysis, spectroscopic analytical techniques and real-time microscopy that is now possible. The analytical microsystem is therefore much better suited to the monitoring, not only of electroactive biofilm formation but also of the expression and disentangling of extracellular electron transfer (EET) catalytic mechanisms. This article reviews the details of the configurations of microfluidic BESs designed for selected objectives and their microfabrication techniques. Because the aim is to manipulate microvolumes and due to the high modularity of the experimental systems, the interfacial conditions between electrodes and electrolytes are perfectly controlled in terms of physicochemistry (pH, nutrients, chemical effectors, etc.) and hydrodynamics (shear, material transport, etc.). Most of the theoretical advances have been obtained thanks to work carried out using models of electroactive bacteria monocultures, mainly to simplify biological investigation systems. However, a huge virgin field of investigation still remains to be explored by taking advantage of the capacities of microfluidic BESs regarding the complexity and interactions of mixed electroactive biofilms.

X-ray pumping of the 229Th nuclear clock isomer.

The metastable first excited state of thorium-229, 229mTh, is just a few electronvolts above the nuclear ground state1-4 and is accessible by vacuum ultraviolet lasers. The ability to manipulate the 229Th nuclear states with the precision of atomic laser spectroscopy5 opens up several prospects6, from studies of fundamental interactions in physics7,8 to applications such as a compact and robust nuclear clock5,9,10. However, direct optical excitation of the isomer and its radiative decay to the ground state have not yet been observed, and several key nuclear structure parameters-such as the exact energies and half-lives of the low-lying nuclear levels of 229Th-remain unknown11. Here we present active optical pumping into 229mTh, achieved using narrow-band 29-kiloelectronvolt synchrotron radiation to resonantly excite the second excited state of 229Th, which then decays predominantly into the isomer. We determine the resonance energy with an accuracy of 0.07 electronvolts, measure a half-life of 82.2 picoseconds and an excitation linewidth of 1.70 nanoelectronvolts, and extract the branching ratio of the second excited state into the ground and isomeric state. These measurements allow us to constrain the 229mTh isomer energy by combining them with γ-spectroscopy data collected over the past 40 years.

Entanglement, holonomic constraints, and the quantization of fundamental interactions

We provide a proof for the necessity of quantizing fundamental interactions demonstrating that a quantum version is needed for any non trivial conservative interaction whose strength depends on the relative distance between two objects. Our proof is based on a consistency argument that in the presence of a classical field two interacting objects in a separable state could not develop entanglement. This requirement can be cast in the form of a holonomic constraint that cannot be satisfied by generic interparticle potentials. Extending this picture of local holonomic constraints, we design a protocol that allows to measure the terms of a multipole expansion of the interaction of two composite bodies. The results presented in this work can pave the way for a study of fundamental interactions based on the analysis of entanglement properties.

Neuroscience, Space and Time

The aim of the present article is to propose possible intersections between contemporary physics and neurosciences, in matters related to space-time. Such scope is of great significance both in “normal” and pathologic situations. In the latter, states like hypermnesia (enhanced capacity to evoke memories, with distortion of information stored in neural circuits) are described, which can be thought of – in a parallel with physics – as space-time scenarios with more than one time-type direction. Dimensions of such category – called Ataiyah-Ward space-time – have been considered in connection with systems of interest in the study of fundamental interactions, and, in macroscopic scale, in association with the issue of gravitational collapse. One has sought to understand physical phenomena in the presence of extra time to then use these studies to propose an attempt to modelling hypermnesia, through the concept that, in certain situations, neuronal system behaves as if immerse in a scenario with two time-type directions.

Top quark physics: A tool for discoveries

The top quark, the heaviest known elementary particle discovered at the Fermilab Tevatron almost twenty years ago, has taken a central role in the study of fundamental interactions. The top quark behaves differently from all other quarks due to its large mass and its correspondingly short lifetime. Its large mass suggests that it may play a special role in nature. The top quark decays before it hadronizes, passing its spin information on to its decay products. Therefore, it is possible to measure observables that depend on the top quark spin, providing a unique environment for tests of the standard model and for new physics searches. With approximately 10 fb−1 of luminosity delivered to each experiment at the Tevatron, and about 20 fb−1 collected by the ATLAS and CMS experiments at the Large Hadron Collider in the first three years of operation, top quark physics is at a turning point from first studies to precision measurements with sensitivity to new physics processes. This report summarizes the latest experimental measurements and studies of top quark properties and rare decays.

Gamma-ray spectroscopy at TRIUMF-ISAC: recent highlights and future plans

High-resolution gamma-ray spectroscopy is essential to fully exploit the unique scientific opportunities at the next generation radioactive beam facilities such as TRIUMF Isotope Separator and Accelerator (ISAC). At ISAC the 8π spectrometer and its associated auxiliary detectors is optimized for β-decay studies while TIGRESS, an array of segmented clover HPGe detectors has been designed for reaction studies with accelerated radioactive ion beams. This paper gives a brief overview of these facilities, recent results from the diverse program of nuclear structure and fundamental interaction studies they support and future plans.

PRENOSOLOGICAL NEURO-PSYCHIATRIC DISORDERS AMONG SCHOOLCHILDREN AND THEIR RELATIONSHIP TO ENVIRONMENTAL FACTORS

Environmental factor is one of the most accurate indicators of determining the health of the population, especially in childhood and adolescence. A significant increase in the amount of data on the status of school health and the environment are the most precise and correct, in view of causation, to evaluate an individual's health at prenosological level in the presence of a specialized database of automated systems. The aim of our study--the study of fundamental interactions and patterns of environmental factors in general and neuropsychiatric disease in schoolchildren of the city of Chelyabinsk. Revealed that among the multi-pollutant air Chelyabinsk first and second rank positions are occupied by selectively harmful to the central nervous system (lead, arsenic, manganese), or have complex adverse effects on the central nervous system, combined with damaging effects on the respiratory and cardio-vascular, urogenital system and blood forming organs, involving the immune mechanism (chromium compounds, lead, arsenic, carbon monoxide and manganese).

A novel method for fundamental interaction studies with an electrostatic ion beam trap

We present the first steps towards the realization of a novel experimental scheme to measure β-ν correlations in the β decay of 6He, for the purpose of Fundamental Interaction studies. Our method is based on a novel use of an ion trapping device, the Electrostatic Ion Beam Trap (EIBT) coupled to a d+t neutron generator. The EIBT which has not been previously considered for Fundamental Interaction studies, exhibits potentially very significant advantages over other state of the art experimental schemes aimed at precision measurements of the β–ν angular correlation coefficient.

REVIEW OF TOP QUARK PHYSICS RESULTS

As the heaviest known fundamental particle, the top quark has taken a central role in the study of fundamental interactions. Production of top quarks in pairs provides an important probe of strong interactions. The top quark mass is a key fundamental parameter which places a valuable constraint on the Higgs boson mass and electroweak symmetry breaking. Observations of the relative rates and kinematics of top quark final states constrain potential new physics. In many cases, the tests available with study of the top quark are both critical and unique. Large increases in data samples from the Fermilab Tevatron have been coupled with major improvements in experimental techniques to produce many new precision measurements of the top quark. The first direct evidence for electroweak production of top quarks has been obtained, with a resulting direct determination of Vtb. Several of the properties of the top quark have been measured. Progress has also been made in obtaining improved limits on potential anomalous production and decay mechanisms. This review presents an overview of recent theoretical and experimental developments in this field. We also provide a brief discussion of the implications for further efforts.

FeCo–Au core-shell nanocrystals

A one-step synthesis of heterostructured high magnetic moment FeCo–Au nanocrystals was demonstrated. The nanocrystals possess a cubic shape and have an average size of 30nm. Compositional analysis revealed the detailed distribution of each element within the nanocrystal. The crystalline structure of the components and their epitaxial relationship were determined by structural analysis. The heterostructured FeCo–Au nanocrystals are promising in biomedical applications as well as in fundamental studies of interactions in the nanoscale.

Francium sources and traps for fundamental interaction studies

Francium is one of the best candidates for atomic parity nonconservation (APNC) and for the search of permanent electric dipole moments (EDMs). APNC measurements test the weak force between electrons and nucleons at very low momentum transfers. They also represent a unique way to detect weak nucleon-nucleon interactions. EDMs are instead related to the time-reversal symmetry. Preliminary to these fundamental measurements are precision studies in atomic spectroscopy and the development of magneto-optical traps (MOT), which partially compensate for the lack of stable Fr isotopes. At LNL Legnaro, francium is produced by fusion of 100-MeV 18O with 197Au in a thick target, followed by evaporation of neutrons from the compound nucleus. Francium diffuses inside the hot target (1200 K) and is surface ionized for injection at 3 keV in an electrostatic beamline. Typically, we produce 1×106 (210Fr ions)/s for a primary flux of 1.5×1012 particles/s. We have studied Fr yields as a function of primary beam energy, intensity, and target temperature. Information on the efficiency of bulk diffusion, surface desorption and ionization is deduced. The beam then enters a Dryfilm-coated cell, where it is neutralized on a heated yttrium plate. The escape time of neutral Fr (diffusion + desorption) is approximately 20 s at 950 K, as measured with a dedicated setup. In the MOT, we use 6 orthogonal Ti:sapphire laser beams for the main pumping transition and 6 beams from a stabilized diode repumper. Fluorescence from trapped atoms is observed with a cooled CCD camera, in order to reach noise levels from stray light equivalent to approximately 50 atoms. Systematic tests are being done to improve the trapping efficiency. We plan to further develop Fr traps at LNL; in parallel, we will study APNC and EDM techniques and systematics with stable alkalis at Pisa, Siena, and Ferrara.

The TRIUMF nuclear structure program and TIGRESS

The isotope separator and accelerator (ISAC) facility located at the TRIUMF laboratory in Vancouver, Canada, is one of the world’s most advanced isotope separator on-line-type radioactive ion beam facilities. An extensive γ-ray spectroscopy programme at ISAC is centred around two major research facilities: (i) the 8π γ-ray spectrometer for β-delayed γ-ray spectroscopy experiments with the low-energy beams from ISAC-I, and (ii) the next generation TRIUMF-ISAC gamma-ray escape suppressed spectrometer (TIGRESS) for in-beam experiments with the accelerated radioactive-ion beams. An overview of these facilities and recent results from the diverse programme of nuclear structure and fundamental interaction studies they support is presented.

Raman scattering and tunable electron–phonon coupling in single layer graphene

Graphene, the two-dimensional hexagonal lattice of carbon atoms, is promising for future electronic devices and for studies of fundamental interactions. New behaviors are linked to the extreme reduction in dimensionality to the atomic level and to the presence of Dirac fermion charge carriers. Here we review our recent work on Raman scattering studies in single layer graphene in which carrier densities are gate-modulated by the electric-field-effect (EFE). The couplings of long wavelength optical phonons (the G -band) with Dirac fermions display remarkable changes in energy and line-width that are tunable by the EFE. In these studies Raman methods emerge as tools for studies of unique properties of charge carriers in graphene such as particle–hole symmetry of Dirac fermions and the impact of disorder.

Muonic atoms with vacant electron shells.

We show that the cascade in muonic atoms with $Z<20$ ejects sufficient atomic electrons to ionize an isolated muonic atom completely. In gases, the rates with which electrons refill the atomic shell can be accurately deduced from measured and calculated electron transfer cross sections. Thus, we can conclude that completely ionized muonic atoms can be prepared in gases, and that they remain isolated for long enough times at attainable pressures to facilitate studies of fundamental interactions in muonic atoms.

Perspectives of Fundamental Physics

Carlo Schaerf (ed) 1979 New York: Harwood Academic vii + 470 pp price $40.75 (paperback) This book arises from a conference held in Rome to celebrate some 50 years of work by the distinguished Italian physicist Edoardo Amaldi. The main aim of the conference was to review the state of present knowledge in the area of physics where Amaldi's contribution has been most significant, namely, the study of fundamental interactions.

A new tool for the study of fundamental interactions: Parity-odd correlations in quark fragmentation

Parity-odd correlations among the fragmentation products of quarks should reveal the longitudinal polarization of these quarks. Possible applications of this idea include a new way to determine the Weinberg angle from data on neutrino reactions, a sensitive test of the quark-antiquark creation picture in e +e − annihilation, a way to determine the weak coupling of hypothetical heavy particles to light quarks and a test for the parton-parton scattering model with elementary gluon exchange for high p⊥ events in nucleon-nucleon collisions.