We present an extensive study of nuclear matrix elements (NME) for the neutrinoless double-beta decay of the nuclei 48Ca, 76Ge, 82Se, 96Zr, 100Mo, 116Cd, 124Sn, 128Te, 130Te, 136Xe, and 150Nd based on state-of-the-art energy density functional methods using the Gogny D1S functional. Beyond-mean-field effects are included within the generating coordinate method with particle number and angular momentum projection for both initial and final ground states. We obtain a rather constant value for the NMEs around 4.7 with the exception of 48Ca and 150Nd, where smaller values are found. We analyze the role of deformation and pairing in the evaluation of the NME and present detailed results for the decay of 150Nd.

We present the first implementation in the (β, γ) plane of the generator coordinate method with full triaxial angular momentum and particle number projected wave functions using the Gogny force. Technical details about the performance of the method and the convergence of the results both in the symmetry restoration and the configuration mixing parts are discussed in detail. We apply the method to the study of 24 Mg, the calculated energies of excited states as well as the transition probabilities are compared to the available experimental data showing a good overall agreement. In addition, we present the RVAMPIR approach which provides a good description of the ground and gamma bands in the absence of strong mixing.

We propose a method for mapping the composition of a surface by using an amplitude modulation atomic force microscope operated without tip-surface mechanical contact. The method consists in exciting the first two modes of the microcantilever. The nonlinear dynamics of the tip motion, the coupling of its first two modes, and the sensitivity of the second mode to long-range attractive forces allows us to use this mode to probe compositional changes while the signal from the first mode is used to image the sample surface. We demonstrate that the second mode has a sensitivity to surface force variations below 10−11 N.

Nuclear matrix elements (NME) for the most promising candidates to detect neutrinoless double beta decay have been computed with energy density functional methods including deformation and pairing fluctuations explicitly on the same footing. The method preserves particle number and angular momentum symmetries and can be applied to any decay without additional fine tunings. The finite range density dependent Gogny force is used in the calculations. An increase of 10%-40% in the NME with respect to the ones found without the inclusion of pairing fluctuations is obtained, reducing the predicted half-lives of these isotopes. The possible detection of lepton number violating processes such as neutrinoless double beta decay (0νββ) is one of the current main goals for particle and nuclear physics research. In this process, an atomic nucleus decays into its neighbor with two neutron less and two proton more emitting only two electrons. Fundamental questions about the nature of the neutrino such as its Dirac or Majorana character, its absolute mass scale as well as its mass hierarchy can be determined if this process is eventually measured [1]. On the one hand, searching for 0νββ decays represents an extremely difficult experimental task because an ultra low background is required to distinguish the predicted scarce events from the noise. Recently, the controversial claim of detection in 76 Ge by the Heidelberg-Moscow (HdM) collaboration [2] has been overruled by the latest data released by . Nevertheless, these results are challenging the experiments that are already running or in an advanced stage of development to detect directly this process [3,[6][7][8][9][10][11][12][13][14]. On the other hand, in the most probable electroweak mechanism to produce 0νββ, namely, the exchange of light Majorana neutrinos [1,15], the half-life of this process is inversely proportional to the effective Majorana neutrino mass m ν , a kinematic phase space factor G 01 and the nuclear matrix elements M 0ν (NME):where m e is the electron mass and m ν = | k U 2 ek m k | is the combination of the neutrino masses m k provided by the neutrino mixing matrix U . The kinematic phase space factor can be determined precisely from the charge, mass and the energy available in the decay [16] while the nuclear matrix elements must be calculated using nuclear structure methods. The most commonly used ones are the quasiparticle random phase approximation [17][18][19][20][21] (QRPA), large scale shell model [22][23][24] (LSSM), interacting boson model [25,26] (IBM), projected HartreeFock-Bogoliubov [27] (PHFB) and energy density functional [28][29][30] (EDF). In recent years, most of the basic nuclear structure aspects of the NMEs have been understood within these different frameworks. In particular, the decay is favored when the initial and final nuclear states have similar intrinsic deformation [28,30,31]. Indications [18,21,23,28,30] about the strong sensitivity of the transition operator to pairing correlations suggest that fluctuations in this degree ...

Working with Hamiltonians from chiral effective field theory, we develop a novel framework for describing arbitrary deformed medium-mass nuclei by combining the in-medium similarity renormalization group with the generator coordinate method. The approach leverages the ability of the first method to capture dynamic correlations and the second to include collective correlations without violating symmetries. We use our scheme to compute the matrix element that governs the neutrinoless double beta decay of 48 Ca to 48 Ti, and find it to have the value 0.61, near or below the predictions of most phenomenological methods. The result opens the door to ab initio calculations of the matrix elements for the decay of heavier nuclei such as 76 Ge, 130 Te, and 136 Xe.

We present the first calculations of a symmetry conserving configuration mixing method (SCCM) using time-reversal symmetry breaking Hartree-Fock-Bogoliubov (HFB) states with the Gogny D1S interaction. The method includes particle number and tridimensional angular momentum symmetry restorations as well as configuration mixing within the generator coordinate method (GCM) framework. The nucleus 32Mg is chosen to show the performance and reliability of the calculations. Additionally, 01+, 21+ and 41+ states are computed for the magnesium isotopic chain, where a noticeable compression of the spectrum is obtained by including cranked states, leading to a very good agreement with the known experimental dataThis work was supported by the Ministerio de Economía y Competitividad under contracts FPA2011-29854-C04-04, BES-2012-059405 and Programa Ramón y Cajal 2012 number 1142

Shape coexistence near the neutron number N= 20: First identification of the E0 decay from the deformed 0 + 2 state in 30 Mg

We present a novel nuclear energy density functional method to calculate spectroscopic properties of atomic nuclei. Intrinsic nuclear quadrupole deformations and rotational frequencies are considered simultaneously as the degrees of freedom within a symmetry conserving configuration mixing framework. The present method allows the study of nuclear states with collective and single-particle character. We calculate the fascinating structure of the semimagic ^{44}S nucleus as a first application of the method, obtaining an excellent quantitative agreement both with the available experimental data and with state-of-the-art shell model calculations.