1. 
 Avetisyan, A., et al.
(författare)

Preface
 2019

Ingår i: APSSE 2019 Actual Problems of System and Software Engineering.  : CEURWS. ; , s. 12

Konferensbidrag (refereegranskat)


2. 
 Karelina, L. N., et al.
(författare)

Scalable memory elements based on rectangular SIsFS junctions
 2021

Ingår i: Journal of Applied Physics.  : AIP Publishing.  00218979 . 10897550. ; 130:17

Tidskriftsartikel (refereegranskat)abstract
 We explore the concept of the Josephson magnetic memory element based on a multilayer twobarrier SIsFS Josephson junction storing the digital state by means of the orientation of magnetization in the Flayer. A diluted PdFe alloy with 1% magnetic atoms is used as a ferromagnet (F), and a tunnel A1Ox layer (I) ensures a high voltage in the resistive state. We have studied two junctions of a rectangular shape in which two digital states are defined by the orientation of the residual Flayer magnetization set along or across the junction in the plane of the ferromagnetic barrier. Implementations of both binary and ternary logic elements are demonstrated. A scalability of rectangular memory elements is analyzed using micromagnetic modeling.


3. 
 Eremeev, S. V., et al.
(författare)

Insight into the electronic structure of the centrosymmetric skyrmion magnet GdRu 2 Si 2
 2023

Ingår i: Nanoscale Advances.  25160230. ; 5:23, s. 66786687

Tidskriftsartikel (refereegranskat)abstract
 The discovery of a square magneticskyrmion lattice in GdRu2Si2, with the smallest so far found skyrmion size and without a geometrically frustrated lattice, has attracted significant attention. In this work, we present a comprehensive study of surface and bulk electronic structures of GdRu2Si2 by utilizing momentumresolved photoemission (ARPES) measurements and firstprinciples calculations. We show how the electronic structure evolves during the antiferromagnetic transition when a peculiar helical order of 4f magnetic moments within the Gd layers sets in. A nice agreement of the ARPESderived electronic structure with the calculated one has allowed us to characterize the features of the Fermi surface (FS), unveil the nested region along kz at the corner of the 3D FS, and reveal their orbital compositions. Our findings suggest that the RudermanKittelKasuyaYosida interaction plays a decisive role in stabilizing the spirallike order of Gd 4f moments responsible for the skyrmion physics in GdRu2Si2. Our results provide a deeper understanding of electronic and magnetic properties of this material, which is crucial for predicting and developing novel skyrmionbased systems.


4. 
 Ade, P. A. R., et al.
(författare)

Planck 2015 results XIV. Dark energy and modified gravity
 2016

Ingår i: Astronomy and Astrophysics.  : EDP Sciences.  00046361 . 14320746. ; 594

Tidskriftsartikel (refereegranskat)abstract
 We study the implications of Planck data for models of dark energy (DE) and modified gravity (MG) beyond the standard cosmological constant scenario. We start with cases where the DE only directly affects the background evolution, considering Taylor expansions of the equation of state w(a), as well as principal component analysis and parameterizations related to the potential of a minimally coupled DE scalar field. When estimating the density of DE at early times, we significantly improve present constraints and find that it has to be below similar to 2% (at 95% confidence) of the critical density, even when forced to play a role for z < 50 only. We then move to general parameterizations of the DE or MG perturbations that encompass both effective field theories and the phenomenology of gravitational potentials in MG models. Lastly, we test a range of specific models, such as kessence, f(R) theories, and coupled DE. In addition to the latest Planck data, for our main analyses, we use background constraints from baryonic acoustic oscillations, typeIa supernovae, and local measurements of the Hubble constant. We further show the impact of measurements of the cosmological perturbations, such as redshiftspace distortions and weak gravitational lensing. These additional probes are important tools for testing MG models and for breaking degeneracies that are still present in the combination of Planck and background data sets. All results that include only background parameterizations (expansion of the equation of state, early DE, general potentials in minimallycoupled scalar fields or principal component analysis) are in agreement with ACDM. When testing models that also change perturbations (even when the background is fixed to ACDM), some tensions appear in a few scenarios: the maximum one found is similar to 2 sigma for Planck TT + lowP when parameterizing observables related to the gravitational potentials with a chosen time dependence; the tension increases to, at most, 3 sigma when external data sets are included. It however disappears when including CMB lensing.


5. 
 Ade, P. A. R., et al.
(författare)

Planck 2015 results XVII. Constraints on primordial nonGaussianity
 2016

Ingår i: Astronomy and Astrophysics.  : EDP Sciences.  00046361 . 14320746. ; 594

Tidskriftsartikel (refereegranskat)abstract
 The Planck full mission cosmic microwave background (CMB) temperature and Emode polarization maps are analysed to obtain constraints on primordial nonGaussianity (NG). Using three classes of optimal bispectrum estimators  separable templatefitting (KSW), binned, and modal we obtain consistent values for the primordial local, equilateral, and orthogonal bispectrum amplitudes, quoting as our final result from temperature alone f(NL)(local) = 2.5 +/ 5.7, f(NL)(equil) = 16 +/ 70, and f(NL)(ortho) = 34 +/ 33 (68% CL, statistical). Combining temperature and polarization data we obtain f(NL)(local) = 0.8 +/ 5.0, f(NL)(equil) = 4 +/ 43, and f(NL)(ortho) = 26 +/ 21 (68% CL, statistical). The results are based on comprehensive crossvalidation of these estimators on Gaussian and nonGaussian simulations, are stable across component separation techniques, pass an extensive suite of tests, and are consistent with estimators based on measuring the Minkowski functionals of the CMB. The effect of timedomain deglitching systematics on the bispectrum is negligible. In spite of these test outcomes we conservatively label the results including polarization data as preliminary, owing to a known mismatch of the noise model in simulations and the data. Beyond estimates of individual shape amplitudes, we present modelindependent, threedimensional reconstructions of the Planck CMB bispectrum and derive constraints on early universe scenarios that generate primordial NG, including general singlefield models of inflation, axion inflation, initial state modifications, models producing parityviolating tensor bispectra, and directionally dependent vector models. We present a wide survey of scaledependent feature and resonance models, accounting for the look elsewhere effect in estimating the statistical significance of features. We also look for isocurvature NG, and find no signal, but we obtain constraints that improve significantly with the inclusion of polarization. The primordial trispectrum amplitude in the local model is constrained to be g(NL)(local) = (9.0 +/ 7.7) x 10(4) (68% CL statistical), and we perform an analysis of trispectrum shapes beyond the local case. The global picture that emerges is one of consistency with the premises of the Lambda CDM cosmology, namely that the structure we observe today was sourced by adiabatic, passive, Gaussian, and primordial seed perturbations.


6. 
 Ade, P. A. R., et al.
(författare)

Planck 2015 results XVIII. Background geometry and topology of the Universe
 2016

Ingår i: Astronomy and Astrophysics.  : EDP Sciences.  00046361 . 14320746. ; 594

Tidskriftsartikel (refereegranskat)abstract
 Maps of cosmic microwave background (CMB) temperature and polarization from the 2015 release of Planck data provide the highest quality fullsky view of the surface of last scattering available to date. This enables us to detect possible departures from a globally isotropic cosmology. We present the first searches using CMB polarization for correlations induced by a possible nontrivial topology with a fundamental domain that intersects, or nearly intersects, the lastscattering surface (at comoving distance chi(rec)), both via a direct scan for matched circular patterns at the intersections and by an optimal likelihood calculation for specific topologies. We specialize to flat spaces with cubic toroidal (T3) and slab (T1) topologies, finding that explicit searches for the latter are sensitive to other topologies with antipodal symmetry. These searches yield no detection of a compact topology with a scale below the diameter of the lastscattering surface. The limits on the radius Ri of the largest sphere inscribed in the fundamental domain (at loglikelihood ratio Delta ln L > 5 relative to a simplyconnected flat Planck bestfit model) are: Ri > 0.97 chi(rec) for the T3 cubic torus; and Ri > 0.56 chi(rec) for the T1 slab. The limit for the T3 cubic torus from the matchedcircles search is numerically equivalent, Ri > 0.97 chi(rec) at 99% confidence level from polarization data alone. We also perform a Bayesian search for an anisotropic global Bianchi VIIh geometry. In the nonphysical setting, where the Bianchi cosmology is decoupled from the standard cosmology, Planck temperature data favour the inclusion of a Bianchi component with a Bayes factor of at least 2.3 units of logevidence. However, the cosmological parameters that generate this pattern are in strong disagreement with those found from CMB anisotropy data alone. Fitting the induced polarization pattern for this model to the Planck data requires an amplitude of 0.10 +/ 0.04 compared to the value of + 1 if the model were to be correct. In the physically motivated setting, where the Bianchi parameters are coupled and fitted simultaneously with the standard cosmological parameters, we find no evidence for a Bianchi VIIh cosmology and constrain the vorticity of such models to (omega/H)(0) < 7.6 x 10(10) (95% CL).


7. 
 Ade, P. A. R., et al.
(författare)

Planck 2015 results XX. Constraints on inflation
 2016

Ingår i: Astronomy and Astrophysics.  : EDP Sciences.  00046361 . 14320746. ; 594

Tidskriftsartikel (refereegranskat)abstract
 We present the implications for cosmic inflation of the Planck measurements of the cosmic microwave background (CMB) anisotropies in both temperature and polarization based on the full Planck survey, which includes more than twice the integration time of the nominal survey used for the 2013 release papers. The Planck full mission temperature data and a first release of polarization data on large angular scales measure the spectral index of curvature perturbations to be n(s) = 0.968 +/ 0.006 and tightly constrain its scale dependence to dn(s)/dln k = 0.003 +/ 0.007 when combined with the Planck lensing likelihood. When the Planck highl polarization data are included, the results are consistent and uncertainties are further reduced. The upper bound on the tensortoscalar ratio is r(0).(002) < 0.11 (95% CL). This upper limit is consistent with the Bmode polarization constraint r < 0.12 (95% CL) obtained from a joint analysis of the BICEP2/Keck Array and Planck data. These results imply that V(phi) proportional to phi(2) and natural inflation are now disfavoured compared to models predicting a smaller tensortoscalar ratio, such as R2 inflation. We search for several physically motivated deviations from a simple powerlaw spectrum of curvature perturbations, including those motivated by a reconstruction of the inflaton potential not relying on the slowroll approximation. We find that such models are not preferred, either according to a Bayesian model comparison or according to a frequentist simulationbased analysis. Three independent methods reconstructing the primordial power spectrum consistently recover a featureless and smooth PR (k) over the range of scales 0.008 Mpc(1) less than or similar to k less than or similar to 0.1 Mpc(1). At large scales, each method finds deviations from a power law, connected to a deficit at multipoles l approximate to 2040 in the temperature power spectrum, but at an uncompelling statistical significance owing to the large cosmic variance present at these multipoles. By combining power spectrum and nonGaussianity bounds, we constrain models with generalized Lagrangians, including Galileon models and axion monodromy models. The Planck data are consistent with adiabatic primordial perturbations, and the estimated values for the parameters of the base Lambda cold dark matter (Lambda CDM) model are not significantly altered when more general initial conditions are admitted. In correlated mixed adiabatic and isocurvature models, the 95% CL upper bound for the nonadiabatic contribution to the observed CMB temperature variance is vertical bar alpha(nonadi)vertical bar < 1.9%, 4.0%, and 2.9% for CDM, neutrino density, and neutrino velocity isocurvature modes, respectively. We have tested inflationary models producing an anisotropic modulation of the primordial curvature power spectrum finding that the dipolar modulation in the CMB temperature field induced by a CDM isocurvature perturbation is not preferred at a statistically significant level. We also establish tight constraints on a possible quadrupolar modulation of the curvature perturbation. These results are consistent with the Planck 2013 analysis based on the nominal mission data and further constrain slowroll singlefield inflationary models, as expected from the increased precision of Planck data using the full set of observations.


8. 
 Aghanim, N., et al.
(författare)

Planck 2015 results XI. CMB power spectra, likelihoods, and robustness of parameters
 2016

Ingår i: Astronomy and Astrophysics.  : EDP Sciences.  00046361 . 14320746. ; 594

Tidskriftsartikel (refereegranskat)abstract
 This paper presents the Planck 2015 likelihoods, statistical descriptions of the 2point correlation functions of the cosmic microwave background (CMB) temperature and polarization fluctuations that account for relevant uncertainties, both instrumental and astrophysical in nature. They are based on the same hybrid approach used for the previous release, i.e., a pixelbased likelihood at low multipoles (l < 30) and a Gaussian approximation to the distribution of crosspower spectra at higher multipoles. The main improvements are the use of more and better processed data and of Planck polarization information, along with more detailed models of foregrounds and instrumental uncertainties. The increased redundancy brought by more than doubling the amount of data analysed enables further consistency checks and enhanced immunity to systematic effects. It also improves the constraining power of Planck, in particular with regard to smallscale foreground properties. Progress in the modelling of foreground emission enables the retention of a larger fraction of the sky to determine the properties of the CMB, which also contributes to the enhanced precision of the spectra. Improvements in data processing and instrumental modelling further reduce uncertainties. Extensive tests establish the robustness and accuracy of the likelihood results, from temperature alone, from polarization alone, and from their combination. For temperature, we also perform a full likelihood analysis of realistic endtoend simulations of the instrumental response to the sky, which were fed into the actual data processing pipeline; this does not reveal biases from residual lowlevel instrumental systematics. Even with the increase in precision and robustness, the Lambda CDM cosmological model continues to offer a very good fit to the Planck data. The slope of the primordial scalar fluctuations, n(s), is confirmed smaller than unity at more than 5 sigma from Planck alone. We further validate the robustness of the likelihood results against specific extensions to the baseline cosmology, which are particularly sensitive to data at high multipoles. For instance, the effective number of neutrino species remains compatible with the canonical value of 3.046. For this first detailed analysis of Planck polarization spectra, we concentrate at high multipoles on the E modes, leaving the analysis of the weaker B modes to future work. At low multipoles we use temperature maps at all Planck frequencies along with a subset of polarization data. These data take advantage of Planck's wide frequency coverage to improve the separation of CMB and foreground emission. Within the baseline Lambda CDM cosmology this requires tau = 0.078 +/ 0.019 for the reionization optical depth, which is significantly lower than estimates without the use of highfrequency data for explicit monitoring of dust emission. At high multipoles we detect residual systematic errors in E polarization, typically at the mu K2 level; we therefore choose to retain temperature information alone for high multipoles as the recommended baseline, in particular for testing nonminimal models. Nevertheless, the highmultipole polarization spectra from Planck are already good enough to enable a separate highprecision determination of the parameters of the Lambda CDM model, showing consistency with those established independently from temperature information alone.


9. 
 Adam, R., et al.
(författare)

Planck 2015 results IX. Diffuse component separation : CMB maps
 2016

Ingår i: Astronomy and Astrophysics.  : EDP Sciences.  00046361 . 14320746. ; 594

Tidskriftsartikel (refereegranskat)abstract
 We present foregroundreduced cosmic microwave background (CMB) maps derived from the full Planck data set in both temperature and polarization. Compared to the corresponding Planck 2013 temperature sky maps, the total data volume is larger by a factor of 3.2 for frequencies between 30 and 70 GHz, and by 1.9 for frequencies between 100 and 857 GHz. In addition, systematic errors in the forms of temperaturetopolarization leakage, analoguetodigital conversion uncertainties, and very long time constant errors have been dramatically reduced, to the extent that the cosmological polarization signal may now be robustly recovered on angular scales l greater than or similar to 40. On the very largest scales, instrumental systematic residuals are still nonnegligible compared to the expected cosmological signal, and modes with l < 20 are accordingly suppressed in the current polarization maps by highpass filtering. As in 2013, four different CMB component separation algorithms are applied to these observations, providing a measure of stability with respect to algorithmic and modelling choices. The resulting polarization maps have rms instrumental noise ranging between 0.21 and 0.27 mu K averaged over 55' pixels, and between 4.5 and 6.1 mu K averaged over 3.'4 pixels. The cosmological parameters derived from the analysis of temperature power spectra are in agreement at the 1 sigma level with the Planck 2015 likelihood. Unresolved mismatches between the noise properties of the data and simulations prevent a satisfactory description of the higherorder statistical properties of the polarization maps. Thus, the primary applications of these polarization maps are those that do not require massive simulations for accurate estimation of uncertainties, for instance estimation of crossspectra and crosscorrelations, or stacking analyses. However, the amplitude of primordial nonGaussianity is consistent with zero within 2 sigma for all local, equilateral, and orthogonal configurations of the bispectrum, including for polarization Emodes. Moreover, excellent agreement is found regarding the lensing Bmode power spectrum, both internally among the various component separation codes and with the bestfit Planck 2015 Lambda cold dark matter model.


10. 
 Adam, R., et al.
(författare)

Planck 2015 results X. Diffuse component separation : Foreground maps
 2016

Ingår i: Astronomy and Astrophysics.  : EDP Sciences.  00046361 . 14320746. ; 594

Tidskriftsartikel (refereegranskat)abstract
 Planck has mapped the microwave sky in temperature over nine frequency bands between 30 and 857 GHz and in polarization over seven frequency bands between 30 and 353 GHz in polarization. In this paper we consider the problem of diffuse astrophysical component separation, and process these maps within a Bayesian framework to derive an internally consistent set of fullsky astrophysical component maps. Component separation dedicated to cosmic microwave background (CMB) reconstruction is described in a companion paper. For the temperature analysis, we combine the Planck observations with the 9yr Wilkinson Microwave Anisotropy Probe (WMAP) sky maps and the Haslam et al. 408 MHz map, to derive a joint model of CMB, synchrotron, freefree, spinning dust, CO, line emission in the 94 and 100 GHz channels, and thermal dust emission. Fullsky maps are provided for each component, with an angular resolution varying between 7: 5 and 1 degrees. Global parameters (monopoles, dipoles, relative calibration, and bandpass errors) are fitted jointly with the sky model, and bestfit values are tabulated. For polarization, the model includes CMB, synchrotron, and thermal dust emission. These models provide excellent fits to the observed data, with rms temperature residuals smaller than 4pK over 93% of the sky for all Planck frequencies up to 353 GHz, and fractional errors smaller than 1% in the remaining 7% of the sky. The main limitations of the temperature model at the lower frequencies are internal degeneracies among the spinning dust, freefree, and synchrotron components; additional observations from external lowfrequency experiments will be essential to break these degeneracies. The main limitations of the temperature model at the higher frequencies are uncertainties in the 545 and 857 GHz calibration and zeropoints. For polarization, the main outstanding issues are instrumental systematics in the 100353 GHz bands on large angular scales in the form of temperaturetopolarization leakage, uncertainties in the analoguetodigital conversion, and corrections for the very long time constant of the bolometer detectors, all of which are expected to improve in the near future.

