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

F. E. A. de Souza, M. O. Tahim, R.I. de Oliveira Junior et al.

Abstract In this work we discuss the issue of localization of $$N=2$$ N = 2 spinning particles. More specifically, we show that we can not confine the spinning particle within the Randall–Sundrum scenario. We argue that this result directly affects studies related to localization of p-form fields. We show that, due to the non confinement of the superparticle, we can not localize p-forms on the membrane.

S. F. Sosnina

A review of epidemiological research of the effects of preconception (prior to conception) radiation exposure to a mother’s body was presented. The anatomical and physiological characteristics that affect radiosensitivity and radioresistance of female reproductive system were reported. Biological prerequisites accounting for different effects of radiation exposure to animals and humans were indicated. The results that were published in open access on epidemiological assessments of the effects of preconception exposure of mothers to the health of their offspring were described based on various cohorts as examples. Analysis of the research work was performed for the cohort of the offspring of atomic bomb survivors in Japan, among the offspring of the individuals affected by radiation accidents and nuclear weapon tests, among the population of the sites with high natural level of radiation. The results of research work among the offspring of female patients exposed to diagnostic and therapeutical radiation and of the offspring of the mothers who were in contact with ionizing radiation sources at workplaces were presented. A special attention was paid to specifics of standardization of occupational exposure of female personnel according to national and international approaches. Generally, it was demonstrated that despite a wide range of epidemiological research works there is still no clear understanding of the effects of preconception exposure of mothers to their offspring. The total results of the analysis of the effects of maternal exposure in preconception period are quite controversial and usually involve a range of uncertainties. In the course of such sort of epidemiological research the following difficulties are indicated: poor verification of medical outcomes, primary data based on questionnaire surveys, lack of detailed information on individual exposure parameters, low statistical power of research works and too short period of follow up of the cohort under research. For this reason, the necessity of further analysis of the effects of exposure of female body was indicated involving detailed risk coefficients of unfavorable reproductive outcomes. Prospective trends for epidemiological analysis of preconception exposure of mothers were indicated. Feasibility of assessment of long-term preconception radiation exposure was described based on the cohort of female workers of Mayak Production Association that is the leading atomic enterprise in the national history.

Rebeca Cabral Gonçalves, Geovana Carvalho Silva, Fernando Lage Araújo Schweizer et al.

This work aims to qualify the use of porous zones for representing fuel assemblies of a proposed SMR reactor in numerical models in other to reduce the computational demand required to study these structures. It employs computational fluid dynamics (CFD) methods to calculate the conservation equations of mass, momentum, and energy within a control volume. Initially, a detailed geometry of the fuel assembly was created and used for isothermal simulations. Based on the results of pressure drop and velocity, equations were used to calculate the coefficients of porosity and pressure drop of the system. These were then utilized to configure a second geometry, consisting of hexahedros divided into thirteen sub-regions according to their cross-sectional area, each having different porosities and pressure drop coefficents. Finally, the results of the two simulations were compared to verify their convergence to allow the use of the porous geometry. The outcomes suggests that, for models with a control volume significantly larger than a single fuel assembly, such as a complete nuclear reactor vessel, the use of porous zones is advantageous, as the variations in average velocity and pressure drop along the length of the structure are small, with the maximum axial velocity variation of -10.99%. However, if the objective is to conduct a more detailed analysis of the entire assembly, this strategy is not recommended, since some specific aspects of fluid behavior are not well capturated, such as radial velocity differences. 

Chunjian Zhang

Sándor Frey, Judit Fogasy, Krisztina Perger et al.

The prominent radio quasar PKS 2215+020 (J2217+0220) was once labelled as a new laboratory for core–jet physics at redshift <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>z</mi><mo>=</mo><mn>3.572</mn></mrow></semantics></math></inline-formula> because of its exceptionally extended jet structure traceable with very long baseline interferometric (VLBI) observations up to a ∼600 pc projected distance from the compact core and a hint of an arcsec-scale radio and an X-ray jet. While the presence of an X-ray jet could not be confirmed later, this active galactic nucleus is still unique at high redshift with its long VLBI jet. Here, we analyse archival multi-epoch VLBI imaging data at five frequency bands from <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>1.7</mn></mrow></semantics></math></inline-formula> to <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>15.4</mn></mrow></semantics></math></inline-formula> GHz covering a period of more than 25 years from 1995 to 2020. We constrain apparent proper motions of jet components in PKS 2215+020 for the first time. Brightness distribution modeling at 8 GHz reveals a nearly <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>0.02</mn></mrow></semantics></math></inline-formula> mas yr⁻¹ proper motion (moderately superluminal with apparently two times the speed of light), and provides <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>δ</mi><mo>=</mo><mn>11.5</mn></mrow></semantics></math></inline-formula> for the Doppler-boosting factor in the inner relativistic jet that is inclined within <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mn>2</mn><mo>∘</mo></msup></semantics></math></inline-formula> to the line of sight and has a <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi mathvariant="sans-serif">Γ</mi><mo>=</mo><mn>6</mn></mrow></semantics></math></inline-formula> bulk Lorentz factor. These values qualify PKS 2215+020 as a blazar, with rather typical jet properties in a small sample of only about 20 objects at <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>z</mi><mo>></mo><mn>3.5</mn></mrow></semantics></math></inline-formula> that have similar measurements to date. According to the 2-GHz VLBI data, the diffuse and extended outer emission feature at ∼60 mas from the core, probably a place where the jet interacts with and decelerated by the ambient galactic medium, is consistent with being stationary, albeit slow motion cannot be excluded based on the presently available data.

R. Garg

V. G. Kupriyanov, M. A. Kurkov, P. Vitale

Abstract We consider gauge theories on Poisson manifolds emerging as semiclassical approximations of noncommutative spacetime with Lie algebra type noncommutativity. We prove an important identity, which allows to obtain simple and manifestly gauge-covariant expressions for the Euler-Lagrange equations of motion, the Bianchi and the Noether identities. We discuss the non-Lagrangian equations of motion, and apply our findings to the κ-Minkowski case. We construct a family of exact solutions of the deformed Maxwell equations in the vacuum. In the classical limit, these solutions recover plane waves with left-handed and right-handed circular polarization, being classical counterparts of photons. The deformed dispersion relation appears to be nontrivial.

Thomas W. Grimm, Erik Plauschinn, Damian van de Heisteeg

Abstract We present a novel strategy to systematically study complex-structure moduli stabilization in Type IIB and F-theory flux compactifications. In particular, we determine vacua in any asymptotic regime of the complex-structure moduli space by exploiting powerful tools of asymptotic Hodge theory. In a leading approximation the moduli dependence of the vacuum conditions are shown to be polynomial with a dependence given by sl(2)-weights of the fluxes. This simple algebraic dependence can be extracted in any asymptotic regime, even though in nearly all asymptotic regimes essential exponential corrections have to be present for consistency. We give a pedagogical introduction to the sl(2)-approximation as well as a detailed step-by-step procedure for constructing the corresponding Hodge star operator. To exemplify the construction, we present a detailed analysis of several Calabi-Yau three- and fourfold examples. For these examples we illustrate that the vacua in the sl(2)-approximation match the vacua obtained with all polynomial and essential exponential corrections rather well, and we determine the behaviour of the tadpole contribution of the fluxes. Finally, we discuss the structure of vacuum loci and their relations to several swampland conjectures. In particular, we comment on the realization of the so-called linear scenario in view of the tadpole conjecture.

Jiale Gu, Shafqat Riaz, Askar B. Abdikamalov et al.

Abstract Bumblebee gravity is one of the simplest gravity theories with spontaneous Lorentz symmetry breaking. Since we know a rotating black hole solution in bumblebee gravity, we can potentially test this model with the available astrophysical observations of black holes. In this work, we construct a reflection model in bumblebee gravity and we use our model to analyze the reflection features of a NuSTAR spectrum of the Galactic black hole EXO 1846-031 in order to constrain the Lorentz-violating parameter $$\ell $$ ℓ . We find that the analysis of the reflection features in the spectrum of EXO 1846-031 cannot constrain the parameter $$\ell $$ ℓ because of a very strong degeneracy between the estimates of $$\ell $$ ℓ and of the black hole spin parameter $$a_*$$ a ∗ . Such a degeneracy may be broken by combining other observations.

Alexei Bazavov, Johannes Heinrich Weber

Spyridon Vossos, Elias Vossos, Christos G. Massouros

This paper shows that gravitational results of general relativity (GR) can be reached by using special relativity (SR) via a SR Lagrangian that derives from the corresponding GR time dilation and vice versa. It also presents a new SR gravitational central scalar generalized potential <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>V</mi><mo>=</mo><mi>V</mi><mo stretchy="false">(</mo><mi>r</mi><mo>,</mo><mover><mi>r</mi><mo>.</mo></mover><mo>,</mo><mover><mi>ϕ</mi><mo>.</mo></mover><mo stretchy="false">)</mo></mrow></semantics></math></inline-formula>, where <i>r</i> is the distance from the center of gravity and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover><mi>r</mi><mo>.</mo></mover><msub><mo>,</mo><mrow></mrow></msub><mover><mi>ϕ</mi><mo>.</mo></mover></mrow></semantics></math></inline-formula> are the radial and angular velocity, respectively. This is associated with the Schwarzschild GR time dilation from where a SR scalar generalized potential is obtained, which is exactly equivalent to the Schwarzschild metric. Thus, the Precession of Mercury’s Perihelion, the Gravitational Deflection of Light, the Shapiro time delay, the Gravitational Red Shift, etc., are explained with the use of SR only. The techniques used in this paper can be applied to any GR spacetime metric, Teleparallel Gravity, etc., in order to obtain the corresponding SR gravitational scalar generalized potential and vice versa. Thus, the case study of Newtonian Gravitational Potential according to SR leads to the corresponding non-Riemannian metric of GR. Finally, it is shown that the mainstream consideration of the Gravitational Red Shift contains two approximations, which are valid in weak gravitational fields only.

Osvaldo L. Santos-Pereira, Everton M. C. Abreu, Marcelo B. Ribeiro

Abstract The Alcubierre warp drive metric is a spacetime geometry featuring a spacetime distortion, called a warp bubble, where a massive particle inside it acquires global superluminal velocities, or warp speeds. This work presents solutions of the Einstein equations for the Alcubierre metric having fluid matter as gravity source. The energy–momentum tensor considered has two fluid contents, the perfect fluid and the parametrized perfect fluid (PPF), a tentative more flexible model whose aim is to explore the possibilities of warp drive solutions with positive matter density content. Santos-Pereira et al. (Eur Phys J C 80:786, 2020) already showed that the Alcubierre metric having dust as source connects this geometry to the Burgers equation, which describes shock waves moving through an inviscid fluid, but led the solutions back to vacuum. The same happened for two out of four solutions subcases for the perfect fluid. Other solutions for the perfect fluid indicate the possibility of warp drive with positive matter density, but at the cost of a complex solution for the warp drive regulating function. Regarding the PPF, solutions were also obtained indicating that warp speeds could be created with positive matter density. Weak, dominant, strong and null energy conditions were calculated for all studied subcases, being satisfied for the perfect fluid and creating constraints in the PPF quantities such that a positive matter density is also possible for creating a warp bubble. Summing up all results, energy–momentum tensors describing more complex forms of matter or field distributions generate solutions for the Einstein equations with the warp drive metric where a negative matter density might not be a strict precondition for attaining warp speeds.

H. Fonvieille, B. Pasquini, N. Sparveris

Christian Drischler, Wick Haxton, Kenneth McElvain et al.

Fernando E. Serna, Roberto Correa da Silveira, J. J. Cobos-Martínez et al.

Abstract The ladder kernel of the Bethe–Salpeter equation is amended by introducing a different flavor dependence of the dressing functions in the heavy-quark sector. Compared with earlier work this allows for the simultaneous calculation of the mass spectrum and leptonic decay constants of light pseudoscalar mesons, the $$D_u$$ D u , $$D_s$$ D s , $$B_u$$ B u , $$B_s$$ B s and $$B_c$$ B c mesons and the heavy quarkonia $$\eta _c$$ η c and $$\eta _b$$ η b within the same framework at a physical pion mass. The corresponding Bethe–Salpeter amplitudes are projected onto the light front and we reconstruct the distribution amplitudes of the mesons in the full theory. A comparison with the first inverse moment of the heavy meson distribution amplitude in heavy quark effective theory is made.

The CMS collaboration, A. M. Sirunyan, A. Tumasyan et al.

Abstract A search for dark matter (DM) particles is performed using events with a Higgs boson candidate and large missing transverse momentum. The analysis is based on proton- proton collision data at a center-of-mass energy of 13 TeV collected by the CMS experiment at the LHC in 2016, corresponding to an integrated luminosity of 35.9 fb −1. The search is performed in five Higgs boson decay channels: h → b b ¯ $$ \mathrm{h}\to \mathrm{b}\overline{\mathrm{b}} $$ , γγ, τ + τ − , W+W − , and ZZ. The results from the individual channels are combined to maximize the sensitivity of the analysis. No significant excess over the expected standard model background is observed in any of the five channels or in their combination. Limits are set on DM production in the context of two simplified models. The results are also interpreted in terms of a spin-independent DM-nucleon scattering cross section and compared to those from direct-detection DM experiments. This is the first search for DM particles produced in association with a Higgs boson decaying to a pair of W or Z bosons, and the first statistical combination based on five Higgs boson decay channels.

The CMS collaboration, A. M. Sirunyan, A. Tumasyan et al.

Abstract A search is presented for the associated production of a standard model Higgs boson with a top quark-antiquark pair ( t t ¯ H $$ \mathrm{t}\overline{\mathrm{t}}\mathrm{H} $$ ), in which the Higgs boson decays into a b quark-antiquark pair, in proton-proton collisions at a centre-of-mass energy s = 13 $$ \sqrt{s}=13 $$ TeV. The data correspond to an integrated luminosity of 35.9 fb−1 recorded with the CMS detector at the CERN LHC. Candidate t t ¯ H $$ \mathrm{t}\overline{\mathrm{t}}\mathrm{H} $$ events are selected that contain either one or two electrons or muons from the t t ¯ $$ \mathrm{t}\overline{\mathrm{t}} $$ decays and are categorised according to the number of jets. Multivariate techniques are employed to further classify the events and eventually discriminate between signal and background. The results are characterised by an observed t t ¯ H $$ \mathrm{t}\overline{\mathrm{t}}\mathrm{H} $$ signal strength relative to the standard model cross section, μ = σ/σ SM, under the assumption of a Higgs boson mass of 125 GeV. A combined fit of multivariate discriminant distributions in all categories results in an observed (expected) upper limit on μ of 1.5 (0.9) at 95% confidence level, and a best fit value of 0.72 ± 0.24(stat) ± 0.38(syst), corresponding to an observed (expected) signal significance of 1.6 (2.2) standard deviations above the background-only hypothesis.

Neil Lambert, Miles Owen

Abstract We study M5-branes wrapped on a multi-centred Taub-NUT space. Reducing to String Theory on the S 1 fibration leads to D4-branes intersecting with D6-branes. D-braneology shows that there are additional charged chiral fermions from the open strings which stretch between the D4-branes and D6-branes. From the M-theory point of view the appearance of these charged states is mysterious as the M5-branes are wrapped on a smooth manifold. In this paper we show how these states arise in the M5-brane worldvolume theory and argue that are governed by a WZWN-like model where the topological term is five-dimensional.

Andreas Helset, Michael Trott

Abstract We discuss interference in the limit m^W2/s→0 $$ {\widehat{m}}_W^2/s\to 0 $$ in the Standard Model Effective Field Theory (SMEFT). Dimension six operators that contribute to ψ¯ψ→ψ¯′1ψ′2ψ¯′3ψ′4 $$ \overline{\psi}\psi \to \overline{\psi}{\prime}_1\psi {\prime}_2\overline{\psi}{\prime}_3\psi {\prime}_4 $$ scattering events can experience a suppression of interference effects with the Standard Model in this limit. This occurs for subsets of phase space in some helicity configurations. We show that approximating these scattering events by 2 → 2 on-shell scattering results for intermediate unstable gauge bosons, and using the narrow width approximation, can miss interference terms present in the full phase space. Such interference terms can be uncovered using off-shell calculations as we explicitly show and calculate. We also study the commutation relation between the SMEFT expansion and the narrow width approximation, and discuss some phenomenological implications of these results.

Naoto Yokoi, Eiji Saitoh

Abstract We discuss a possible principle for detecting dark matter axions in galactic halos. If axions constitute a condensate in the Milky Way, stimulated emissions of the axions from a type of excitation in condensed matter can be detectable. We provide general mechanism for the dark matter emission, and, as a concrete example, an emission of dark matter axions from magnetic vortex strings in a type II superconductor is investigated along with possible experimental signatures.