Disentangling phase transitions and critical points in the proton-neutron interacting boson model by catastrophe theory

We introduce the basic concepts of catastrophe theory needed to derive analytically the phase diagram of the proton-neutron interacting boson model (IBM-2). Previous studies [1-3] were based on numerical solutions. We here explain the whole IBM-2 phase diagram including the precise order of the phase transitions in terms of the cusp catastrophe. © 2014 The Authors.This work was partially supported by the Spanish Ministerio de Econom´ıa y Competitividad and the European regional development fund (FEDER) under Project Nos. FIS2011-28738-C02-01, FIS2011-28738-C02-02, FIS2012-34479, and by Junta de Andaluc´ıa under Project Nos. FQM160, P11-FQM-7632 and FQM318, as well as by Spanish Consolider-Ingenio 2010 (CPANCSD2007-00042).Peer Reviewe

Decoherence due to an excited-state quantum phase transition in a two-level boson model

10 págs.; 8 figs.; 2 tabs.; PACS number s : 03.65.Yz, 05.70.Fh, 64.70.TgThe decoherence induced on a single qubit by its interaction with the environment is studied. The environment is modeled as a scalar two-level boson system that can go through either first-order or continuous-excited-state quantum phase transitions, depending on the values of the control parameters. A mean-field method based on the Tamm-Damkoff approximation is worked out in order to understand the observed behavior of the decoherence. Only the continuous-excited-state phase transition produces a noticeable effect in the decoherence of the qubit. This is maximal when the system-environment coupling brings the environment to the critical point for the continuous phase transition. In this situation, the decoherence factor (or the fidelity) goes to zero with a finite-size scaling power law. © 2009 The American Physical Society.This work has been partially supported by the Spanish Ministerio de Educación y Ciencia and by the European regional development fund FEDER under Projects No. FIS2008-04189, No. FIS2006-12783-C03-01, No. FPA2006- 13807-C02-02, and No. FPA2007-63074, by CPAN-Ingenio, by Comunidad de Madrid under Project No. 200650M012, CSIC, and by Junta de Analucía under Projects No. FQM160, No. FQM318, No. P05-FQM437, and No. P07- FQM-02962. A.R. is supported by the Spanish program “Juan de la Cierva” and P. P-F. is supported by a FPU grant of the Spanish Ministerio de Educación y Ciencia.Peer Reviewe

Continuous unitary transformations in two-level boson systems

17 págs.; 16 figs.; 1 tab.; 3 apéndices ; PACS number(s): 21.60.Fw, 21.10.Re, 05.10.Cc, 75.40.CxTwo-level boson systems displaying a quantum phase transition from a spherical (symmetric) to a deformed (broken) phase are studied. A formalism to diagonalize Hamiltonians with O(2L+1) symmetry for large number of bosons is worked out. Analytical results beyond the simple mean-field treatment are deduced by using the continuous unitary transformations technique. In this scheme, a 1/N expansion for different observables is proposed and allows one to compute the finite-size scaling exponents at the critical point. Analytical and numerical results are compared and reveal the power of the present approach to compute the finite-size corrections in such a context. © 2005 The American Physical Society.S. Dusuel gratefully acknowledges financial support of the DFG in SP1073. This work has been partially supported by the Spanish DGI under projects FIS2005-01105, BFM2003-05316-C02-02, BFM2003-05316, and FPA2003-05958.Peer Reviewe

New results on q-positivity

In this paper we discuss symmetrically self-dual spaces, which are simply real vector spaces with a symmetric bilinear form. Certain subsets of the space will be called q-positive, where q is the quadratic form induced by the original bilinear form. The notion of q-positivity generalizes the classical notion of the monotonicity of a subset of a product of a Banach space and its dual. Maximal q-positivity then generalizes maximal monotonicity. We discuss concepts generalizing the representations of monotone sets by convex functions, as well as the number of maximally q-positive extensions of a q-positive set. We also discuss symmetrically self-dual Banach spaces, in which we add a Banach space structure, giving new characterizations of maximal q-positivity. The paper finishes with two new examples.Comment: 18 page

Two-neutron separation energies, binding energies and phase transitions in the interacting boson model

In the framework of the interacting boson model the three transitional regions (rotational-vibrational, rotational-$\gamma$-unstable and, vibrational-$\gamma$-unstable transitions) are reanalyzed. A new kind of plot is presented for studying phase transitions in finite systems such as atomic nuclei. The importance of analyzing binding energies and not only energy spectra and electromagnetic transitions, describing transitional regions is emphasized. We finally discuss a number of realistic examples.Comment: 34 pages, TeX (ReVTeX). 12 ps figures. 3 tables. Submitted to Nucl. Phys.

The Pt isotopes: comparing the Interacting Boson Model with Configuration Mixing and the Extended Consistent-Q formalism

The role of intruder configurations in the description of energy spectra and B(E2) values in the Pt region is analyzed. In particular, we study the differences between Interacting Boson Model calculations with or without the inclusion of intruder states in the even Pt nuclei $^{172-194}$Pt. As a result, it shows that for the description of a subset of the existing experimental data, i.e., energy spectra and absolute B(E2) values up to an excitation energy of about 1.5 MeV, both approaches seem to be equally valid. We explain these similarities between both model spaces through an appropriate mapping. We point out the need for a more extensive comparison, encompassing a data set as broad (and complete) as possible to confront with both theoretical approaches in order to test the detailed structure of the nuclear wave functions.Comment: To be published in NP

alpha-particle production in the scattering of 6He by 208Pb at energies around the Coulomb barrier

New experimental data from the scattering of 6He+208Pb at energies around and below the Coulomb barrier are presented. The yield of breakup products coming from projectile fragmentation is dominated by a strong group of $\alpha$ particles. The energy and angular distributions of this group have been analyzed and compared with theoretical calculations. This analysis indicates that the $\alpha$ particles emitted at backward angles in this reaction are mainly due to two-neutron transfer to weakly bound states of the final nucleus.Comment: 20 pages, 5 figures. Nuclear Physics A792 (2007) 2-1

Correction to: A Phase II Study Evaluating Combined Neoadjuvant Cetuximab and Chemotherapy Followed by Chemoradiotherapy and Concomitant Cetuximab in Locoregional Oesophageal Cancer Patients

Errors were subsequently identified in the article and the following corrections should be note

Theoretical uncertainties on quasielastic charged-current neutrino-nucleus cross sections

We estimate the theoretical uncertainties of the model developed in [J. Nieves, J.E. Amaro, M. Valverde, Phys. Rev. C 70 (2004) 055503] for inclusive quasielastic charged-current neutrino-nucleus reactions at intermediate energies. Besides we quantify the deviations of the predictions of this many body framework from those obtained within a simple Fermi gas model. A special attention has been paid to the ratio sigma(mu)/sigma(e) of interest for experiments on atmospheric neutrinos. We show that uncertainties affecting this ratio are likely smaller than 5%