Three-body forces and proton-rich nuclei

We present the first study of three-nucleon (3N) forces for proton-rich nuclei along the N=8 and N=20 isotones. Our results for the ground-state energies and proton separation energies are in very good agreement with experiment where available, and with the empirical isobaric multiplet mass equation. We predict the spectra for all N=8 and N=20 isotones to the proton dripline, which agree well with experiment for 18Ne, 19Na, 20Mg and 42Ti. In all other cases, we provide first predictions based on nuclear forces. Our results are also very promising for studying isospin symmetry breaking in medium-mass nuclei based on chiral effective field theory.Comment: 5 pages, 4 figures, minor changes, published versio

Two-neutrino double electron capture on 124^{124}Xe based on an effective theory and the nuclear shell model

We study the two-neutrino double electron capture on $^{124}$Xe based on an effective theory (ET) and large-scale shell model calculations, two modern nuclear structure approaches that have been tested against Gamow-Teller and double-beta decay data. In the ET, the low-energy constants are fit to electron capture and $\beta^{-}$ transitions around xenon. For the nuclear shell model, we use an interaction in a large configuration space that reproduces the spectroscopy of nuclei in this mass region. For the dominant transition to the $^{124}$Te ground state, we find half-lives $T^{2\nu{\rm ECEC}}_{1/2}=(1.3-18)\times 10^{22}$ y for the ET and $T^{2\nu{\rm ECEC}}_{1/2} = (0.43-2.9)\times 10^{22}$ y for the shell model. The ET uncertainty leads to a half-life almost entirely consistent with present experimental limits and largely within the reach of ongoing experiments. The shell model half-life range overlaps with the ET, but extends less beyond current limits. Our findings thus suggest that the two-neutrino double electron capture on $^{124}$Xe has a good chance to be discovered by ongoing or future experiments. In addition, we present results for the two-neutrino double electron capture to excited states of $^{124}$Te.Comment: 5 pages, 2 figure

Uncertainties in constraining low-energy constants from 3^3H β\beta decay

We discuss the uncertainties in constraining low-energy constants of chiral effective field theory from $^3$H $\beta$ decay. The half-life is very precisely known, so that the Gamow-Teller matrix element has been used to fit the coupling $c_D$ of the axial-vector current to a short-range two-nucleon pair. Because the same coupling also describes the leading one-pion-exchange three-nucleon force, this in principle provides a very constraining fit, uncorrelated with the $^3$H binding energy fit used to constrain another low-energy coupling in three-nucleon forces. However, so far such $^3$H half-life fits have only been performed at a fixed cutoff value. We show that the cutoff dependence due to the regulators in the axial-vector two-body current can significantly affect the Gamow-Teller matrix elements and consequently also the extracted values for the $c_D$ coupling constant. The degree of the cutoff dependence is correlated with the softness of the employed NN interaction. As a result, present three-nucleon forces based on a fit to $^3$H $\beta$ decay underestimate the uncertainty in $c_D$. We explore a range of $c_D$ values that is compatible within cutoff variation with the experimental $^3$H half-life and estimate the resulting uncertainties for many-body systems by performing calculations of symmetric nuclear matter.Comment: 9 pages, 11 figures, published version, includes Erratum, which corrects Figs. 2-6 due to the incorrect c_D relation between 3N forces and two-body currents use

Coexistence of spherical states with deformed and superdeformed bands in doubly magic 40-Ca; A shell model challenge

Large scale shell model calculations, with dimensions reaching 10**9, are carried out to describe the recently observed deformed (ND) and superdeformed (SD) bands based on the first and second excited 0+ states of 40-Ca at 3.35-MeV and 5.21-MeV respectively. A valence space comprising two major oscillator shells, sd and pf, can accommodate most of the relevant degrees of freedom of this problem. The ND band is dominated by configurations with four particles promoted to the pf-shell (4p-4h in short). The SD band by 8p-8h configurations. The ground state of 40-Ca is strongly correlated, but the closed shell still amounts to 65%. The energies of the bands are very well reproduced by the calculations. The out-band transitions connecting the SD band with other states are very small and depend on the details of the mixing among the different np-nh configurations, in spite of that, the calculation describes them reasonably. For the in-band transition probabilities along the SD band, we predict a fairly constant transition quadrupole moment Q_0(t)~170 e fm**2 up to J=10, that decreases toward the higher spins. We submit also that the J=8 states of the deformed and superdeformed band are maximally mixed.Comment: 12 pages, 9 figure

Microwave-assisted CO2 reforming of coke oven gas: An exception to the general rule?

It has been previously reported that the dry reforming of methane can be enhanced by means of microwave heating. In this article, this technology is applied to the CO2 reforming of coke oven gas (COG). The results obtained were opposite to those reported in the CO2 reforming of CH4, since in the case of the COG, microwave heating only slightly enhanced the conversions when an activated carbon was used as catalyst, whereas the results achieved when mixtures of activated carbon and Ni/Al 2O3 were employed as catalyst were even worse than those obtained in a conventional oven. Several hypotheses were considered in order to find an explanation for these poor results, the nature of the microplasmas formed during the process being the most likely factor. The high proportions of H2 present in the reactor when the dry reforming of coke oven gas is carried out may give rise to microplasmas of higher temperature than in the dry reforming of CH4. This will cause the Ni particles to sinter significantly, leading to a decrease in the conversions

Microwave-assisted CO2 reforming of coke oven gas: An exception to the general rule?

It has been previously reported that the dry reforming of methane can be enhanced by means of microwave heating. In this article, this technology is applied to the CO2 reforming of coke oven gas (COG). The results obtained were opposite to those reported in the CO2 reforming of CH4, since in the case of the COG, microwave heating only slightly enhanced the conversions when an activated carbon was used as catalyst, whereas the results achieved when mixtures of activated carbon and Ni/Al 2O3 were employed as catalyst were even worse than those obtained in a conventional oven. Several hypotheses were considered in order to find an explanation for these poor results, the nature of the microplasmas formed during the process being the most likely factor. The high proportions of H2 present in the reactor when the dry reforming of coke oven gas is carried out may give rise to microplasmas of higher temperature than in the dry reforming of CH4. This will cause the Ni particles to sinter significantly, leading to a decrease in the conversions

Coherent elastic neutrino-nucleus scattering: EFT analysis and nuclear responses

The cross section for coherent elastic neutrino-nucleus scattering (CEνNS) depends on the response of the target nucleus to the external current, in the Standard Model (SM) mediated by the exchange of a Z boson. This is typically subsumed into an object called the weak form factor of the nucleus. Here, we provide results for this form factor calculated using the large-scale nuclear shell model for a wide range of nuclei of relevance for current CEνNS experiments, including cesium, iodine, argon, fluorine, sodium, germanium, and xenon. In addition, we provide the responses needed to capture the axial-vector part of the cross section, which does not scale coherently with the number of neutrons, but may become relevant for the SM prediction of CEνNS on target nuclei with nonzero spin. We then generalize the formalism allowing for contributions beyond the SM. In particular, we stress that in this case, even for vector and axial-vector operators, the standard weak form factor does not apply anymore, but needs to be replaced by the appropriate combination of the underlying nuclear structure factors. We provide the corresponding expressions for vector, axial-vector, but also (pseudo)scalar, tensor, and dipole effective operators, including two-body-current effects as predicted from chiral effective field theory (EFT). Finally, we update the spin-dependent structure factors for dark matter scattering off nuclei according to our improved treatment of the axial-vector responses

Microwave-assisted CO2 reforming of coke oven gas: An exception to the general rule?

It has been previously reported that the dry reforming of methane can be enhanced by means of microwave heating. In this article, this technology is applied to the CO2 reforming of coke oven gas (COG). The results obtained were opposite to those reported in the CO2 reforming of CH4, since in the case of the COG, microwave heating only slightly enhanced the conversions when an activated carbon was used as catalyst, whereas the results achieved when mixtures of activated carbon and Ni/Al 2O3 were employed as catalyst were even worse than those obtained in a conventional oven. Several hypotheses were considered in order to find an explanation for these poor results, the nature of the microplasmas formed during the process being the most likely factor. The high proportionsof H2 present in the reactor when the dry reforming of coke oven gas is carried out may give rise to microplasmas of higher temperature than in the dry reforming of CH4. This will cause the Ni particles to sinter significantly, leading to a decrease in the conversions

Picking on the family: disrupting android malware triage by forcing misclassification

Machine learning classification algorithms are widely applied to different malware analysis problems because of their proven abilities to learn from examples and perform relatively well with little human input. Use cases include the labelling of malicious samples according to families during triage of suspected malware. However, automated algorithms are vulnerable to attacks. An attacker could carefully manipulate the sample to force the algorithm to produce a particular output. In this paper we discuss one such attack on Android malware classifiers. We design and implement a prototype tool, called IagoDroid, that takes as input a malware sample and a target family, and modifies the sample to cause it to be classified as belonging to this family while preserving its original semantics. Our technique relies on a search process that generates variants of the original sample without modifying their semantics. We tested IagoDroid against RevealDroid, a recent, open source, Android malware classifier based on a variety of static features. IagoDroid successfully forces misclassification for 28 of the 29 representative malware families present in the DREBIN dataset. Remarkably, it does so by modifying just a single feature of the original malware. On average, it finds the first evasive sample in the first search iteration, and converges to a 100% evasive population within 4 iterations. Finally, we introduce RevealDroid*, a more robust classifier that implements several techniques proposed in other adversarial learning domains. Our experiments suggest that RevealDroid* can correctly detect up to 99% of the variants generated by IagoDroid

Shape coexistence and superdeformation in 28^{28}Si

We study the shape coexistence of differently deformed states within $^{28}$Si using shell-model and beyond-mean-field techniques. Experimentally, $^{28}$Si exhibits shape coexistence between an oblate ground state and an excited prolate structure. The oblate rotational band is described well within the $sd$ shell using the USDB interaction. However, for the prolate band, a modification of this interaction is required, lowering the single-particle energy of the $1d_{3/2}$ orbit. Furthermore, we explore the possibility of a superdeformed configuration in $^{28}$Si. Our calculations, spanning both the $sd$ and $pf$ shells, rule out the existence of a superdeformed $0^+$ bandhead within an excitation energy range of 10-20 MeV.Comment: 6 pages, 4 figures. To be published in XXXVII Mazurian Lakes Conference Proceeding