Hasil untuk "Nuclear and particle physics. Atomic energy. Radioactivity"

Giulio Salvatori

Abstract How to turn the flip of a coin into a random variable whose expected value equals a scattering amplitude? We answer this question by constructing a numerical algorithm to evaluate curve integrals — a novel formulation of scattering amplitudes — by a Monte Carlo strategy. To achieve a satisfactory accuracy we take advantage of tropical importance sampling. The crucial result is that the sampling procedure can be realized as a stochastic process on surfaces which can be simulated efficiently on a computer. The key insight is to let go of the Feynman-bias that amplitudes should be presented as a sum over diagrams, and instead re-arrange the sum as suggested by a dual decomposition of curve integrals. We attach an implementation of this algorithm as an ancillary file, which we have used to evaluate amplitudes for the massive Tr(ϕ)3 theory in D = 2 space-time dimensions, up to 10-loops. Interestingly, we observe experimentally that the number of sample points required to achieve a fixed accuracy remains significantly smaller than what the number of diagrams would suggest. Finally we propose an extension of our method which is inspired by ideas from artificial intelligence. We use the stochastic process to define a parametrization for a space of distributions, where we formulate importance sampling for an arbitrary curve integrand as a convex optimization problem.

Matthias Heinz

Renormalization group methods generate low-resolution Hamiltonians that are more diagonal and easier to solve. This chapter reviews the similarity renormalization group for nuclear Hamiltonians, which is a popular method for generating low-resolution nuclear forces. It presents the similarity renormalization group flow equations, analyzes how the similarity renormalization group drives the Hamiltonian towards the diagonal, and studies the effect of induced many-body interactions. It concludes by highlighting the progress in first-principles calculations of nuclei driven by low-resolution nuclear Hamiltonians.

L. E. Sinclair, D. A. McCormack

Canada, a Tier 1 nuclear nation involved in uranium mining and refining, operating nuclear power reactors, and with a Small Modular Reactor action plan, maintains a rigorous nuclear security infrastructure. The Nuclear Emergency Response team at Natural Resources Canada fulfills federal mandates in high-sensitivity air- and ground-based mobile survey for prevention, detection and response. A robust operational framework exists for deployment of traditional large-volume NaI(Tl)-based detection suites. At the same time, a research arm examines emerging non-nuclear technologies which can enhance the capabilities of the operational team. Herein, the potential for uncrewed mobile systems in nuclear security and emergency response operations is discussed. The impact of new technologies such as silicon photomultipliers, gamma imagers and self-shielding directional detectors is presented, and the use of high-performance computing in modelling of system response functions is discussed. Finally, a capability to extrapolate to the location of a source some distance away from a survey trajectory is shown. The extrapolation method includes propagation of the measurement error to the extrapolated region, essential information for nuclear response operators to know if a region is actually clear of radioactivity or not.

Tadashi Togashi, Shigeki Owada, Toshinori Yabuuchi et al.

We have developed a timing control system to stabilize the long-term timing drift between X-ray free-electron laser (XFEL) and optical laser pulses using an out-of-loop balanced optical-microwave phase detector and an arrival-timing monitor for pump–probe experiments at the SPring-8 Ångstrom Compact free-electron LAser (SACLA). The timing jitter and drift between the XFEL and the optical laser pulses have been reduced to less than 50 fs (RMS) over ∼49 h. The performance of the timing stabilization system was investigated by measuring the correlation of the long-term simultaneous timing monitoring on two branches of BL3 over 8 h. A linear correlation was observed with an RMS error of 8.6 fs.

Antonella Cid, Israel Obreque

Abstract We perform a dynamical system analysis and a Bayesian model selection for a new set of interacting scenarios in the framework of modified holographic Ricci dark energy (MHR-IDE) models. The dynamical analysis shows a modified radiation epoch and a late-time attractor corresponding to an accelerated phase of holographic dark energy. In the Bayesian comparison, we use a combination of background data including type Ia supernovae, cosmic chronometers, the local value of the Hubble constant, baryon acoustic oscillations, and cosmic microwave background data. We find evidence against all the MHR-IDE scenarios studied in comparison with the $$\varLambda $$ Λ CDM when the full joint analysis is considered.

Manosh T. Manoharan

Abstract In holographic dark energy (HDE) models, infrared cut-offs with derivatives of the Hubble parameter, such as the Granda–Oliveros cut-off, offer a coherent explanation for late-time acceleration while ensuring causal consistency. We show that such HDE will inevitably mimic the dominant energy forms unless we forcefully calibrate the free parameters. This feature reveals the dependency between the model’s ability to explain the late-time acceleration and the integration constant, highlighting that one cannot arbitrarily set this constant to zero. We see that the origins of HDE and the Friedmann equations from the first law of horizon thermodynamics offer a natural explanation for this behaviour. Thus, the holographic principle naturally extends to all energy components, diverging from the prevalent notion in HDE models. The model also allows dark energy to transit from an early negative energy to a present positive value, with a singular dark energy equation of state parameter, which can relax the tension in the BAO Lyman- $$\alpha $$ α observations. Furthermore, we present observational constraints utilizing Pantheon $$^+,$$ + , OHD, CMB Shift parameter, QSO and BAO data, indicating the presence of early negative energy as an unavoidable consequence. Upon using the SH0ES prior, we see that the model accounts for the Hubble parameter at the cost of affecting the matter density while simultaneously relaxing the tensions in BAO Lyman- $$\alpha $$ α observations and the age estimations. This study also underscores notable features stemming from the comprehensive utilization of the covariance matrix within cosmic chronometers, BAO and CMB distance prior and clarifies the implications of negative dark energy density derived from the high redshift Pantheon $$^+$$ + sample. Additionally, we provide a brief overview of the theoretical framework surrounding linear perturbation within the wGOHDE model.

Bruno Berganholi, Gláuber C. Dorsch, Beatriz M. D. Sena et al.

We present a concise pedagogic introduction to group representation theory motivated by the historical developments surrounding the advent of the Eightfold Way. Abstract definitions of groups and representations are avoided in favour of the physical intuition of symmetries of the nuclear interaction. The concept of nuclear isospin is used as a physical motivation to introduce SU(2) and discuss the main techniques of representation theory. The discovery of strange particles motivates extending the symmetry group to SU(3), at first in the context of the Sakata model. We highlight the successes in fitting mesons in the SU(3) octet, discuss the drawbacks of the Sakata model for baryonic classifications, and how the Eightfold Way finally led to the quark model. This approach has two major advantages: (i) the main concepts of the theory of Lie groups are introduced and discussed without ever losing touch with its applications in particle physics; (ii) it allows the beginner to study group theory while also becoming acquainted with the historical developments of particle physics that led to the concept of quarks. In particular, in this pedagogical path the quarks appear as yet another class of particles predicted from symmetry principles, rather than being introduced ad hoc for postulating an SU(3) symmetry, as usually done in the literature.

Michele Arzano, Alessandra D’Alise, Domenico Frattulillo

Abstract We consider sets of states in conformal quantum mechanics associated to generators of time evolution whose orbits cover different regions of the time domain. States labelled by a continuous global time variable define the two-point correlation functions of the theory seen as a one-dimensional conformal field theory. Such states exhibit the structure of a thermofield double built on bipartite eigenstates of generators of non-global time evolution. In terms of the correspondence between radial conformal symmetries in Minkowski space-time and time evolution in conformal quantum mechanics proposed in [1, 2] these generators coincide with conformal Killing vectors tangent to worldlines of Milne and diamond observers at constant radius. The temperature of the thermofield double states in conformal quantum mechanics reproduces the temperatures perceived by such diamond and Milne observers. We calculate the entanglement entropy associated to the thermofield double states and obtain a UV divergent logarithmic behaviour analogous to known results in two-dimensional conformal field theory in which the entangling boundary is point-like.

А.В. Павлов, А.М. Жилкашинова, С.С. Герт et al.

In the present paper the research results of influence of nanoparticles TiO2 additions in the range 0,1 — 2,0 wt. % on electrophysical properties of oxide-beryllium ceramics (BeO + TiO2) made of micropowders are presented. The electrophysical characteristics of synthesized ceramics modified with 30 wt. % TiO2 microand nanoparticles in the electric current frequency range of 100 Hz — 100 MHz were studied by the total complex resistance method (impedance). It is known that the introduction of TiO2 addition to the BeOceramics after heat treatment in a reducing atmosphere is accompanied by a significant increase in electrical conductivity and the ability to absorb electromagnetic radiation in a wide range of frequencies. According to the results of the studies it was found that the addition of nanoparticles TiO2 into the (BeO + TiO2)-ceramics significantly reduces its static electrical resistance in comparison with the serial sample, and the specific conductivity of such ceramics significantly increases at high frequencies ~ 107 Hz. The addition of TiO2 nanoparticles significantly increases the dielectric losses of the sample sintered in the temperature range 1530 — 1550 °C. The values of real and imaginary parts of dielectric permittivity of such ceramics and the tangent of the angle of dielectric loss are two times higher compared to the serial sample — BT-30 (B — beryllium, T — titanium). The obtained results are unique in their kind, due to the experiment with a rare and strategically important material — beryllium oxide and the possibility of synthesizing new nanostructures based on it.

Hyun-Sik Jeong, Matteo Baggioli, Keun-Young Kim et al.

Abstract The holographic superconductor is one of the most popular models in the context of applied holography. Despite what its name suggests, it does not describe a superconductor. On the contrary, the low temperature phase of its dual field theory is a superfluid with a spontaneously broken U(1) global symmetry. As already observed in the previous literature, a bona fide holographic superconductor can be constructed using mixed boundary conditions for the bulk gauge field. By exploiting this prescription, we study the near-equilibrium collective dynamics in the Higgs phase and reveal the characteristic features of the Anderson-Higgs mechanism. We show that second sound disappears from the spectrum and the gauge field acquires a finite energy gap of the order of the plasma frequency. We observe an overdamped to underdamped crossover for the Higgs mode which acquires a finite energy gap below ≈ T c /2, with T c the superconducting critical temperature. Interestingly, the energy gap of the Higgs mode at low temperature is significantly smaller than 2∆, with ∆ the superconducting energy gap. Finally, we interpret our results using Ginzburg-Landau theory and we confirm the validity of previously derived perturbative analytic expressions.

Chen Zhang, Chaofeng Sang, Yuqiang Tao et al.

The new lower tungsten divertor of EAST uses a right-angle shape consisted by horizontal and vertical targets, which has the capacity of increasing the divertor closure. The strike point (SP) sweeping experiment is carried out to (1) avoid long-term deposition of particle and heat flux at the same location, thus protecting the target, (2) study the dependence of power control capability on the SP location. The particle and energy flux densities to the target depends strongly on their decay width. Therefore, it is important to know how the SP location influences the outer target (OT) particle parallel λ _js _,OT and OT parallel heat flux decay widths λ _q _,OT . In this work, SOLPS-ITER simulations combined with SP sweeping experiment are applied to study this issue. Four cases, which are taken from different time during SP sweeping (including both horizontal and vertical divertor) in L-mode experiment with high heating power, are selected for investigation. The simulation result is in satisfactory agreement with experiment data, suggesting the simulation is valid. The results indicate that the SP location can affect neutral particles accumulation and ionization positions, thus affecting λ _js _,OT and λ _q _,OT . (1) When SP is located in horizontal target, the higher neutral particle ionization in common flux region leads to wider λ _js _,OT than those of vertical target. (2) When SP is located on horizontal target, the divertor power radiation is higher than that of vertical target, resulting in wider λ _q _,OT . (3) Increasing upstream plasma density can effectively broaden λ _q _,OT , while λ _js _,OT remains almost unchanged. This study improves the understanding of the influence of divertor shape on λ _js _,OT and λ _q _,OT , and can be applied to heat flux control during long-pulse high-power discharges on EAST.

Igor R. Klebanov, Vladimir Narovlansky, Zimo Sun et al.

Abstract A pair of the 2D non-unitary minimal models M(2, 5) is known to be equivalent to a variant of the M(3, 10) minimal model. We discuss the RG flow from this model to another non-unitary minimal model, M(3, 8). This provides new evidence for its previously proposed Ginzburg-Landau description, which is a ℤ2 symmetric theory of two scalar fields with cubic interactions. We also point out that M(3, 8) is equivalent to the (2, 8) superconformal minimal model with the diagonal modular invariant. Using the 5-loop results for theories of scalar fields with cubic interactions, we exhibit the 6 − ϵ expansions of the dimensions of various operators. Their extrapolations are in quite good agreement with the exact results in 2D. We also use them to approximate the scaling dimensions in d = 3, 4, 5 for the theories in the M(3, 8) universality class.

Gordon Arrowsmith-Kron, Michail Athanasakis-Kaklamanakis, Mia Au et al.

Molecules containing short-lived, radioactive nuclei are uniquely positioned to enable a wide range of scientific discoveries in the areas of fundamental symmetries, astrophysics, nuclear structure, and chemistry. Recent advances in the ability to create, cool, and control complex molecules down to the quantum level, along with recent and upcoming advances in radioactive species production at several facilities around the world, create a compelling opportunity to coordinate and combine these efforts to bring precision measurement and control to molecules containing extreme nuclei. In this manuscript, we review the scientific case for studying radioactive molecules, discuss recent atomic, molecular, nuclear, astrophysical, and chemical advances which provide the foundation for their study, describe the facilities where these species are and will be produced, and provide an outlook for the future of this nascent field.

Yan Liu, Hong-Da Lyu

Abstract We study the interior structure of five dimensional neutral helical black holes in Einstein gravity and charged helical black holes in Einstein-Maxwell gravity. Inside the neutral helical black holes, the systems evolve to a stable spacelike Kasner singularity. The metric field related to the helical deformation strength exhibits oscillation behavior close to the horizon at low temperature and small helical deformation strength. Inside the charged helical black holes, we show that the inner Cauchy horizon can not exist. The systems also evolve from the horizon to a stable Kasner singularity. We find that the oscillations can exist and there is a special feature that the oscillations occur near the horizon and before the collapse of the Einstein-Rosen bridge for the charged helical black holes.

Dongxia Feng, Meichen Ji, Haiqing Liao et al.

Anthropogenic radionuclides of plutonium and 137Cs in the environment were usually applied for tracing the environmental impact of nuclear activities as well as establishing the chronology of recent lake sediment. In this study, the vertical distribution and spatial differentiation of plutonium and 137Cs in lake sediments of China were systematically contrastive analyzed to elucidate the regional influence by the local fallout from Chinese nuclear tests. The results demonstrated that the inventory of 137Cs and 239,240Pu, and their isotopic composition in lake sediments in northwestern China were obviously different from other regions, indicating that a portion of radionuclides in lakes in northwest China were originated from the Chinese Lop Nor Nuclear Test site (CNTs), and radionuclides in lakes of other regions may be completely originated from global fallout. Usually, the anthropogenic radionuclides recorded in lake sediments showed a single peak corresponding to the maximum deposition of 1964. However, two or three accumulation peaks of radionuclides were also observed in a few lakes. For the application of radionuclides on the dating of recent sediment, the accumulative peak of 239,240Pu and 137Cs signed to the period of 1963–1964 is the only practicable time marker for lake sediments in other regions of China. Isotopic information, such as 240Pu/239Pu ratio and 239,240Pu/137Cs activity ratio, may be useful for accurate sediment chronology, as well as used as a fingerprint to identify the source of the associated radioactive substance in the environment.

Enrico Bothmann, Andy Buckley, Ilektra A. Christidi et al.

Abstract Poor computing efficiency of precision event generators for LHC physics has become a bottleneck for Monte-Carlo event simulation campaigns. We provide solutions to this problem by focusing on two major components of general-purpose event generators: The PDF evaluator and the matrix-element generator. For a typical production setup in the ATLAS experiment, we show that the two can consume about 80% of the total runtime. Using NLO simulations of $$pp\rightarrow \ell ^+\ell ^-+\text {jets}$$ p p → ℓ + ℓ - + jets and $$pp\rightarrow t\bar{t}+\text {jets}$$ p p → t t ¯ + jets as an example, we demonstrate that the computing footprint of Lhapdf and Sherpa can be reduced by factors of order 10, while maintaining the formal accuracy of the event sample. The improved codes are made publicly available.

Jiangyong Jia, Giuliano Giacalone, Chunjian Zhang

Bulk nuclear structure properties, such as radii and deformations, leave distinct signatures in the final state of relativistic heavy-ion collisions. Isobaric collisions offer an easy route to establish explicit connections between the colliding nuclei's structure and the observable outcomes. Here, we investigate the effects of nuclear skin thickness and nuclear deformations on the elliptic flow ($v_2$) and its fluctuations in high-energy $^{96}$Ru+$^{96}$Ru and $^{96}$Zr+$^{96}$Zr collisions. Our findings reveal that the difference in skin thickness between these isobars only influences the inherent ellipticity of the collision systems, $v_2^{\mathrm{rp}}$. In contrast, differences in nuclear deformations solely impact the fluctuations of $v_2$ around $v_2^{\mathrm{rp}}$. Hence, we have identified a data-driven method to disentangle the effects of nuclear skin and nuclear deformations, marking a significant step toward assessing the consistency of nuclear phenomena across energy scales.

M. Raineri, M. Gallardo, J. Reyna Almandos et al.

A capillary pulsed-discharge and a theta-pinch were used to record Kr spectra in the region of 330–4800 Å. A set of 168 transitions of these spectra were classified for the first time. We extended the analysis to twenty-five new energy levels belonging to 3s²3p²4d, 3s²3p²5d even configurations. We calculated weighted transition probabilities (gA) for all of the experimentally observed lines and lifetimes for new energy levels using a relativistic Hartree–Fock method, including core-polarization effects.

Djuna Croon, Gilly Elor, Rebecca K. Leane et al.

Abstract New light particles produced in supernovae can lead to additional energy loss and a consequent deficit in neutrino production in conflict with the neutrinos observed from Supernova 1987A (SN1987A). Contrary to the majority of previous SN1987A studies, we examine the impact of Z′ bosons, axions, and axion-like particles (ALPs) interacting with the muons produced in SN1987A. For the first time, we find constraints on generic Z′ bosons coupled to muons, and apply our results to particle models including gauged L μ −L τ number, U 1 L μ − L τ $$ \mathrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$ , and gauged B − L number, U(1) B−L . We constrain Z′ bosons with masses up to about 250 − 500 MeV, and down to about 10 −9 in Z′-muon coupling. We also extend previous work on axion-muon couplings by examining the importance of loop-level interactions, as well as performing calculations over a wider range of axion masses. We constrain muon-coupled axions from arbitrarily low masses up to about 200 − 500 MeV, with bounds extending down to axion-muon couplings of approximately 10 −8 GeV −1. We conclude that supernovae broadly provide a sensitive probe of new lightly-coupled particles interacting with muons.