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The mass of the axion, a particle that is central to many dark-matter theories, is calculated via the equation of state of the Universe and the temperature dependence of the so-called topological susceptibility of quantum chromodynamics. Weighing up axions as a window on dark matter Calculations that need to consider the theory of quantum chromodynamics, which describes how the strong interaction holds quarks together, are daunting because of the nonlinearity of the strong force. Despite the numerical difficulties, Szabolcs Borsanyi et al . have managed to perform an accurate calculation of the mass of an axion. These particles are at the heart of many dark-matter theories. Key in this paper is the ability to calculate the equation of state and the so-called topological susceptibility of quantum chromodynamics over a very wide temperature range. With their determination of the axion mass, the authors make important predictions about the evolution of the Universe that will help to test dark-matter theories involving axions in the near future. Unlike the electroweak sector of the standard model of particle physics, quantum chromodynamics (QCD) is surprisingly symmetric under time reversal. As there is no obvious reason for QCD being so symmetric, this phenomenon poses a theoretical problem, often referred to as the strong CP problem. The most attractive solution for this 1 requires the existence of a new particle, the axion 2 , 3 —a promising dark-matter candidate. Here we determine the axion mass using lattice QCD, assuming that these particles are the dominant component of dark matter. The key quantities of the calculation are the equation of state of the Universe and the temperature dependence of the topological susceptibility of QCD, a quantity that is notoriously difficult to calculate 4 , 5 , 6 , 7 , 8 , especially in the most relevant high-temperature region (up to several gigaelectronvolts). But by splitting the vacuum into different sectors and re-defining the fermionic determinants, its controlled calculation becomes feasible. Thus, our twofold prediction helps most cosmological calculations 9 to describe the evolution of the early Universe by using the equation of state, and may be decisive for guiding experiments looking for dark-matter axions. In the next couple of years, it should be possible to confirm or rule out post-inflation axions experimentally, depending on whether the axion mass is found to be as predicted here. Alternatively, in a pre-inflation scenario, our calculation determines the universal axionic angle that corresponds to the initial condition of our Universe.

The existence and stability of atoms rely on the fact that neutrons are more massive than protons. The measured mass difference is only 0.14% of the average of the two masses. A slightly smaller or larger value would have led to a dramatically different universe. Here, we show that this difference results from the competition between electromagnetic and mass isospin breaking effects. We performed lattice quantum-chromodynamics and quantum-electrodynamics computations with four nondegenerate Wilson fermion flavors and computed the neutron-proton mass-splitting with an accuracy of 300 kilo–electron volts, which is greater than 0 by 5 standard deviations. We also determine the splittings in the Σ, Ξ, D, and Ξcc isospin multiplets, exceeding in some cases the precision of experimental measurements.

The standard model of particle physics describes the vast majority of experiments and observations involving elementary particles. Any deviation from its predictions would be a sign of new, fundamental physics. One long-standing discrepancy concerns the anomalous magnetic moment of the muon, a measure of the magnetic field surrounding that particle. Standard-model predictions 1 exhibit disagreement with measurements 2 that is tightly scattered around 3.7 standard deviations. Today, theoretical and measurement errors are comparable; however, ongoing and planned experiments aim to reduce the measurement error by a factor of four. Theoretically, the dominant source of error is the leading-order hadronic vacuum polarization (LO-HVP) contribution. For the upcoming measurements, it is essential to evaluate the prediction for this contribution with independent methods and to reduce its uncertainties. The most precise, model-independent determinations so far rely on dispersive techniques, combined with measurements of the cross-section of electron–positron annihilation into hadrons 3 – 6 . To eliminate our reliance on these experiments, here we use ab initio quantum chromodynamics (QCD) and quantum electrodynamics simulations to compute the LO-HVP contribution. We reach sufficient precision to discriminate between the measurement of the anomalous magnetic moment of the muon and the predictions of dispersive methods. Our result favours the experimentally measured value over those obtained using the dispersion relation. Moreover, the methods used and developed in this work will enable further increased precision as more powerful computers become available. A precise theoretical computation of the anomalous magnetic moment of the muon based on ab initio quantum chromodynamics and quantum electrodynamics calculations is presented, which favours the existing experimental values.

A bstract The effect of an external (electro)magnetic field on the finite temperature transition of QCD is studied. We generate configurations at various values of the quantized magnetic flux with N f  = 2 + 1 flavors of stout smeared staggered quarks, with physical masses. Thermodynamic observables including the chiral condensate and susceptibility, and the strange quark number susceptibility are measured as functions of the field strength. We perform the renormalization of the studied observables and extrapolate the results to the continuum limit using N t  = 6 , 8 and 10 lattices. We also check for finite volume effects using various lattice volumes. We find from all of our observables that the transition temperature T c significantly decreases with increasing magnetic field. This is in conflict with various model calculations that predict an increasing T c ( B ). From a finite volume scaling analysis we find that the analytic crossover that is present at B  = 0 persists up to our largest magnetic fields eB  ≈ 1 GeV 2 , and that the transition strength increases mildly up to this eB  ≈ 1 GeV 2 .

A bstract We present the equation of state (pressure, trace anomaly, energy density and entropy density) of the SU(3) gauge theory from lattice field theory in an unprecedented precision and temperature range. We control both finite size and cut-off effects. The studied temperature window (0.7…1000 T c ) stretches from the glueball dominated system into the perturbative regime, which allows us to discuss the range of validity of these approaches. We also determine the preferred renormalization scale of the Hard Thermal Loop scheme and we fit the unknown g 6 order perturbative coefficient at extreme high temperatures T >  100 T c . We furthermore quantify the nonperturbative contribution to the trace anomaly using a simple functional form. Our high precision data allows one to have a complete theoretical description of the equation of state from T  = 0 all the way to the phase transition, through the transition region into the perturbative regime up to the Stefan-Boltzmann limit. We will discuss this description, too.

A universal transition The standard model of particle physics predicts two phase transitions that are relevant for the evolution of the early Universe. One, the quantum chromodynamics transition, involves the strong force that binds quarks into protons and neutrons. Despite much theoretical effort, the nature of this transition remains ambiguous. Now Aoki et al . report computationally demanding calculations that suggest that there was no true phase transition. Instead, an analytic crossover took place, involving a rapid, continuous change with temperature as opposed to a jump. This means that it will be difficult to find experimental evidence of a transition from astronomical observations. The standard model of particle physics predicts two transitions that are relevant for the evolution of the early Universe. Computationally demanding calculations now reveal that a real phase transition did not occur, but rather an analytic crossover, involving a rapid change (as opposed to a jump) as the temperature varies. Quantum chromodynamics (QCD) is the theory of the strong interaction, explaining (for example) the binding of three almost massless quarks into a much heavier proton or neutron—and thus most of the mass of the visible Universe. The standard model of particle physics predicts a QCD-related transition that is relevant for the evolution of the early Universe. At low temperatures, the dominant degrees of freedom are colourless bound states of hadrons (such as protons and pions). However, QCD is asymptotically free, meaning that at high energies or temperatures the interaction gets weaker and weaker 1 , 2 , causing hadrons to break up. This behaviour underlies the predicted cosmological transition between the low-temperature hadronic phase and a high-temperature quark–gluon plasma phase (for simplicity, we use the word ‘phase’ to characterize regions with different dominant degrees of freedom). Despite enormous theoretical effort, the nature of this finite-temperature QCD transition (that is, first-order, second-order or analytic crossover) remains ambiguous. Here we determine the nature of the QCD transition using computationally demanding lattice calculations for physical quark masses. Susceptibilities are extrapolated to vanishing lattice spacing for three physical volumes, the smallest and largest of which differ by a factor of five. This ensures that a true transition should result in a dramatic increase of the susceptibilities. No such behaviour is observed: our finite-size scaling analysis shows that the finite-temperature QCD transition in the hot early Universe was not a real phase transition, but an analytic crossover (involving a rapid change, as opposed to a jump, as the temperature varied). As such, it will be difficult to find experimental evidence of this transition from astronomical observations.

More than 99% of the mass of the visible universe is made up of protons and neutrons. Both particles are much heavier than their quark and gluon constituents, and the Standard Model of particle physics should explain this difference. We present a full ab initio calculation of the masses of protons, neutrons, and other light hadrons, using lattice quantum chromodynamics. Pion masses down to 190 mega-electron volts are used to extrapolate to the physical point, with lattice sizes of approximately four times the inverse pion mass. Three lattice spacings are used for a continuum extrapolation. Our results completely agree with experimental observations and represent a quantitative confirmation of this aspect of the Standard Model with fully controlled uncertainties.

We determine the phase diagram of QCD on the μ − T plane for small to moderate chemical potentials. Two transition lines are defined with two quantities, the chiral condensate and the strange quark number susceptibility. The calculations are carried out on N t =6 , 8 and 10 lattices generated with a Symanzik improved gauge and stout-link improved 2+ 1 flavor staggered fermion action using physical quark masses. After carrying out the continuum extrapolation we find that both quantities result in a similar curvature of the transition line. Furthermore, our results indicate that in leading order the width of the transition region remains essentially the same as the chemical potential is increased.

IntroductionMagnocellular deficit in visual perception and impaired emotion recognition are core features of schizophrenia, however their relationship and the neurobiological underpinnings are still unclear.ObjectivesThe aim of our research was to investigate the oscillatory background of perception and emotion recognition in schizophrenia and to examine the relationship between these processes.MethodsThirty-nine subjects with schizophrenia and forty healthy controls subjects were enrolled in the study; the two study groups did not differ in age, gender and education. In the visual paradigm the participants viewed magnocellular biased low-spatial frequency (LSF) and parvocellular biased high-spatial frequency (HSF) Gabor-patches and in the second paradigm happy, sad and neutral faces were presented, while 128-channel EEG was recorded.ResultsSignificantly weaker theta (4-7 Hz) event related synchronisation (ERS) was observed in patients compared to controls in the LSF condition, whereas in the HSF condition there was no difference between the two groups. Event related changes in theta amplitude were also found to be significantly weaker in patients compared to healthy controls in the emotion recognition task, which difference was disappeared after correction for ERS to LSF condition. In the correlational analysis theta activity in the magnocellular biased stimuli correlated significantly with theta activity in the emotion recognition task, while theta to parvocellular biased stimuli showed no similar correlation with emotion recognition.ConclusionsIn schizophrenia, emotion recognition impairments are closely related to the dysfunction of the magnocellular system, which supports the bottom-up model of schizophrenia.DisclosureNo significant relationships.

IntroductionWhile decreased alpha-band functional connectivity (FC) and changes in network topology have been reported in Alzheimer’s disease, it is not yet entirely known whether these differences mark cognitive decline in the early stages of the disease.ObjectivesOur study aimed to analyze EEG FC and network differences in the alpha frequency band during visuospatial memory maintenance between Mild Cognitive Impairment (MCI) patients and healthy elderly with subjective memory complaints.MethodsFC and network structure of 17 MCI patients and 20 control participants were studied with 128-channel EEG during a visuospatial memory task. FC was measured by amplitude envelope correlation with leakage correction (AEC-c), while network analysis was performed by applying the Minimum Spanning Tree approach.ResultsIncreasing memory load enhanced the mean alpha-band FC in the control group. In contrast to that, after an initial increase, the MCI group showed significantly (p<0.05) diminished FC in the highest memory load condition. Mean alpha AEC-c correlated significantly with the size and mean diffusivity of medial temporal lobe structures in the entire sample. The network analysis revealed a rerouted network in the MCI group with a more centralized topology and a more unequal traffic load distribution compared to the control group.ConclusionsAlpha-band FC correlates with cognitive load-related modulation, with medial temporal lobe atrophy, and with the disruption of hippocampal fiber integrity in the earliest stages of cognitive decline. The more integrated network topology of the MCI group is in line with the “hub overload and failure” framework and might be part of a compensatory mechanism.DisclosureNo significant relationships.