6062 research outputs found
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MODELLING STAR FORMATION AND AGN FEEDBACK IN COSMOLOGICAL SIMULATIONS
No full text<p>Invited talk at a conference.</p>
Cosmology and fundamental physics with the ELT-ANDES spectrograph
No full textState-of-the-art 19th century spectroscopy led to the discovery of quantum mechanics, and 20th century spectroscopy led to the confirmation of quantum electrodynamics. State-of-the-art 21st century astrophysical spectrographs, especially ANDES at ESO's ELT, have another opportunity to play a key role in the search for, and characterization of, the new physics which is known to be out there, waiting to be discovered. We rely on detailed simulations and forecast techniques to discuss four important examples of this point: big bang nucleosynthesis, the evolution of the cosmic microwave background temperature, tests of the universality of physical laws, and a real-time model-independent mapping of the expansion history of the universe (also known as the redshift drift). The last two are among the flagship science drivers for the ELT. We also highlight what is required for the ESO community to be able to play a meaningful role in 2030s fundamental cosmology and show that, even if ANDES only provides null results, such 'minimum guaranteed science' will be in the form of constraints on key cosmological paradigms: these are independent from, and can be competitive with, those obtained from traditional cosmological probes
Origin of the spectral features observed in the cosmic-ray spectrum
No full textContext. Recent measurements reveal the presence of several features in the cosmic-ray (CR) spectrum. In particular, the proton and helium spectra exhibit a spectral hardening at ≈300 GV and a spectral steepening at ≈15 TV, followed by the well-known knee-like feature at ≈3 PV. The spectra of heavier nuclei also harden at ≈300 GV, while no claim can be currently made about the presence of the ≈15 TV softening, due to low statistics. In addition, the B/C ratio also exhibits a hardening at ≈100 GeV/n and seems to be rather shallow at ≈1 TeV/nAims. We propose a possible explanation of the observed spectral features in the framework of a composite diffusion scenario and considering different classes of sources.Methods. The proposed scenario is based on two assumptions. First, in the Galactic disk, where magnetic field lines are mainly oriented along the Galactic plane, particle scattering is assumed to be very inefficient. Therefore, the transport of CRs from the disk to the halo is set by the magnetic field line random walk induced by large-scale turbulence. Second, we propose that the spectral steepening at ≈15 TV is related to the typical maximum rigidity reached in the acceleration of CRs by the majority of supernova remnants, while we assume that only a fraction of sources, contributing to ≈10 − 20% of the CR population, can accelerate particles up to ∼PV rigidities.Results. Within this framework we show that it is possible to reproduce the proton and helium spectra from GV to multi-PV; the p/He ratio; the spectra of CRs from lithium to iron; the p̄ flux and the p̄/p ratio; and the abundance ratios B/C, B/O, C/O, Be/C, Be/O, and Be/B. We also discuss the 10Be/9Be ratio in view of the recent AMS02 preliminary measurements.Key words: diffusion / cosmic rays / Galaxy: disk / Galaxy: hal
A quantum k-nearest neighbors algorithm based on the Euclidean distance estimation
No full textThe k-nearest neighbors (k-NN) is a basic machine learning (ML) algorithm, and several quantum versions of it, employing different distance metrics, have been presented in the last few years. Although the Euclidean distance is one of the most widely used distance metrics in ML, it has not received much consideration in the development of these quantum variants. In this article, a novel quantum k-NN algorithm based on the Euclidean distance is introduced. Specifically, the algorithm is characterized by a quantum encoding requiring a low number of qubits and a simple quantum circuit not involving oracles, aspects that favor its realization. In addition to the mathematical formulation and some complexity observations, a detailed empirical evaluation with simulations is presented. In particular, the results have shown the correctness of the formulation, a drop in the performance of the algorithm when the number of measurements is limited, the competitiveness with respect to some classical baseline methods in the ideal case, and the possibility of improving the performance by increasing the number of measurements
Effective action approach to the dynamical map
No full textThe dynamical map represents a fundamental concept in quantum field theory, providing a solution of the field equations in the Fock space of asymptotic fields. In this paper, we show how to express the dynamical map of a scalar field in the language of quantum effective action. This grants us new insights into the study of topological defects in quantum field theory by showing a connection between the usual least-action principle and Umezawa's boson transformation method
Robust bounds on ALP dark matter from dwarf spheroidal galaxies in the optical MUSE-Faint survey
No full textNearby dwarf spheroidal galaxies are ideal targets in the search for indirect dark matter (DM) signals.In this work, we analyze MUSE spectroscopic observations of a sample of five galaxies, composed of both classical and ultra-faint dwarf spheroidals. The goal is to search for radiative decays of axion-like particles (ALPs) in the mass range of 2.7–5.3 eV. After taking into account the uncertainties associated with the DM spatial distribution in the galaxies, we derive robust bounds on the effective ALP-two-photon coupling.They lie well below the QCD axion band and are significantly more constraining than limits from other probes, in the relevant mass range.We also test the possible presence of a positive signal, concluding that none of the wavelength channels selected for this analysis, i.e., not affected by large background contamination, is exhibiting such evidence
The design and technology development of the JUNO central detector
No full textThe Jiangmen Underground Neutrino Observatory (JUNO) is a large-scale neutrino experiment with multiple physics goals including determining the neutrino mass hierarchy, the accurate measurement of neutrino oscillation parameters, the neutrino detection from supernovae, the Sun, and the Earth, etc. JUNO puts forward physically and technologically stringent requirements for its central detector (CD), including a large volume and target mass (20 kt liquid scintillator, LS), a high-energy resolution (3% at 1 MeV), a high light transmittance, the largest possible photomultiplier (PMT) coverage, the lowest possible radioactive background, etc. The CD design, using a spherical acrylic vessel with a diameter of 35.4 m to contain the LS and a stainless steel structure to support the acrylic vessel and PMTs, was chosen and optimized. The acrylic vessel and the stainless steel structure will be immersed in pure water to shield the radioactive background and bear great buoyancy. The challenging requirements of the acrylic sphere have been achieved, such as a low intrinsic radioactivity and high transmittance of the manufactured acrylic panels, the tensile and compressive acrylic node design with embedded stainless steel pad, and one-time polymerization for multiple bonding lines. Moreover, several technical challenges of the stainless steel structure have been solved: the production of low radioactivity stainless steel material, the deformation and precision control during production and assembly, and the usage of high-strength stainless steel rivet bolt and of high friction efficient linkage plate. Finally, the design of the ancillary equipment such as the LS filling, overflowing, and circulating system was done
Prospects for open heavy-flavour and quarkonium measurements with NA60+
No full textThe high-intensity beams provided by the CERN SPS in a large range of energies offer a unique opportunity to investigate the region of the QCD phase diagram at high baryochemical potential.The NA60+ experiment, proposed for taking data with heavy-ion collisions at the SPS in the next years, is in an ideal position to provide new insights into the QCD phase diagram, measuring rare probes via a Pb-Pb and p-A beam-energy scan, in the collisions energy interval = 6-17 GeV.NA60+ plans to measure the production of hidden and open charm hadrons and prospects on these measurements will be discussed.Open charm hadrons will be measured from their decays into charged hadrons, reconstructed from the tracks in the silicon detectors of the vertex telescope.This will enable high-precision measurements of the yield of D, D, and D mesons, and of baryons, thus allowing us to constrain the transport properties of the QGP and the charm-quark hadronisation.Charmonium states, J/ and (2S), will be measured through dimuon decays reconstructed with the muon spectrometer.Hence, by measuring the charmonium yield in p-A and Pb-Pb collisions at different collision energies, NA60+ will have a unique opportunity to study the threshold energy for the onset of deconfinement
Novel Planetary Signatures from the Dark Universe
No full text"Dunkle Materie" (DM) came from unexpected cosmological observations. Nowadays within our solar system, diverse observations also defy conventional explanations, like the main physical process(es) underlying the heating of the different solar atmospheric layers. Streaming DM offers a viable common scenario following gravitational focusing by the solar system bodies. This fits as the underlying process behind the solar cycle, which was the first signature suggesting a planetary dependency. The challenge, since 1859, is to find a remote planetary impact, beyond the extremely feeble planetary tidal force. We stress the possible involvement of an external impact by some overlooked "streaming invisible matter", which reconciles all investigated mysterious observations mimicking a not extant remote planetary force. Unexpected planetary relationships exist for both the dynamic Sun and Earth, reflecting multiple signatures for streaming DM. The local reasoning à la Zwicky is also suggestive for searches including puzzling biomedical phenomena. Favourite DM candidates are anti-quark-nuggets, magnetic monopoles, dark photons, or the composite "pearls". Then, anomalies within the solar system are the manifestation of the dark Universe. The tentative streaming DM scenario enhances spatiotemporally the DM flu
Gravitational waves induced by scalar-tensor mixing
No full textThis paper explores the physics of second-order gravitational waves (GWs) induced by scalar-tensor perturbation interactions in the radiation-dominated Universe. We investigate the distinctive signatures of these GWs and their detectability compared to scalar-induced GWs. Unlike scalar-scalar induced GWs, scalar-tensor induced GWs do not present resonances or a logarithmic running in the low frequency tail in the case of peaked primordial spectra. But, interestingly, they partly inherit any primordial parity violation of tensor modes. We find that chirality in primordial GWs can lead to distinguishing effects in scalar-tensor induced GWs in the ultraviolet (UV) region. We also address a potential divergence in our GWs and explore possible solutions. This study contributes to our understanding of GWs in the early Universe and their implications for cosmology and GWs detection