Quantum Phase Transitions in the Interacting Boson Model: Integrability, level repulsion and level crossing

We study the quantum phase transition mechanisms that arise in the Interacting Boson Model. We show that the second-order nature of the phase transition from U(5) to O(6) may be attributed to quantum integrability, whereas all the first-order phase transitions of the model are due to level repulsion with one singular point of level crossing. We propose a model Hamiltonian with a true first-order phase transition for finite systems due to level crossings.Comment: Accepted in PR

Thermal diagnostic of the Optical Window on board LISA Pathfinder

Vacuum conditions inside the LTP Gravitational Reference Sensor must comply with rather demanding requirements. The Optical Window (OW) is an interface which seals the vacuum enclosure and, at the same time, lets the laser beam go through for interferometric Metrology with the test masses. The OW is a plane-parallel plate clamped in a Titanium flange, and is considerably sensitive to thermal and stress fluctuations. It is critical for the required precision measurements, hence its temperature will be carefully monitored in flight. This paper reports on the results of a series of OW characterisation laboratory runs, intended to study its response to selected thermal signals, as well as their fit to numerical models, and the meaning of the latter. We find that a single pole ARMA transfer function provides a consistent approximation to the OW response to thermal excitations, and derive a relationship with the physical processes taking place in the OW. We also show how system noise reduction can be accomplished by means of that transfer function.Comment: 20 pages, 14 figures; accepted for publication in Class. Quantum Gra

Mean field study of structural changes in Pt isotopes with the Gogny interaction

The evolution of the nuclear shapes along the triaxial landscape is studied in the Pt isotopic chain using the selfconsistent Hartree-Fock-Bogoliubov approximation based on the Gogny interaction. In addition to the parametrization D1S, the new incarnations D1N and D1M of this force are also included in our analysis to asses to which extent the predictions are independent of details of the effective interaction. The considered range of neutron numbers 88<N<26 includes prolate, triaxial, oblate and spherical ground state shapes and serves for a detailed comparison of the predictions obtained with the new sets D1N and D1M against the ones provided by the standard parametrization Gogny-D1S in a region of the nuclear landscape for which experimental and theoretical fingerprints of shape transitions have been found. Structural evolution along the Pt chain is discussed in terms of the deformation dependence of single particle energies.Comment: 18 pages, 10 figures. Accepted for publication in Phys. Rev.

Hallazgos electromiográficos y electroneurográficos en el pie cavo esencial

La etiología del pie cavo cuando ésta es conocida, suele ser debida a un trastorno de tipo neurológico o miopático, aunque en determinados casos nos encontramos con pacientes que padecen esta deformidad en el pie, en los cuales no podemos descubrir ningún antecedente de este tipo, por lo que lo calificamos de pie cavo «esencial». A un grupo de estos pacientes con pie cavo «esencial», en los que no hemos encontrado ningún tipo de antecedente neurológico, lo hemos sometido a una exploración electroneurográfica, encontrando que la mitad de ellos padecían algún trastorno neuropático/miopático, que no había sido detectado en la exploración clínica inicial.Neurological or myopathic diseases are frequently involved in the etiology of flat foot. In some cases, no antecedents of disease can be found and therefore these flat foots are classified as «essential». We have undertaken an electrophysiologic study in a series of patients with «essential» flat food in order to explore unsuspected neurological disorders. In half of the patients, neuropathic and myopathic electroneurographic patterns of different severity were detected

Two-neutron transfer reactions as a tool to study the interplay between shape coexistence and quantum phase transitions

The goal of this study is to find an observable that could distinguish between both phenomena, shape coexistence and quantum phase transitions. The selected observable to be analyzed is the two-neutron transfer intensity between the 0+ states in the parent and daughter nuclei. The framework in which the study is done is the Interacting Boson Model (IBM), including its version with configuration mixing (IBM-CM). In order to generate the wave functions of the isotope chains of interest, needed for calculating transfer intensities, previous systematic studies with IBM and IBM-CM are taken without changing the parameters. Results for two-neutron transfer intensities are presented for Zr, Hg and Pt isotopic chains using IBM-CM and, moreover, the same is done for Zr, Pt and Sm isotopic chains using IBM with just a single configuration, i.e., without using configuration mixing. In the case of Zr, the two-neutron transfer intensities between the ground states provide a clear observable indicating that normal and intruder configurations coexist in the low-lying spectrum and that they cross at A=98->100, and this could allow to disentangle whether or not shape coexistence is inducing a given QPT. In the case of Pt, where shape coexistence is present and the regular and the intruder configurations cross for the ground state, there is almost no influence in the value of the two-neutron transfer, neither in the case of Hg where the ground state always has regular nature. For the Sm isotope chain that is one of the quantum phase transition paradigms, the value of the two-neutron transfer is strongly affected.Comment: To be published in the Chinese Physics

Relationship between X(5)-models and the interacting boson model

The connections between the X(5)-models (the original X(5) using an infinite square well, X(5)-$\beta^8$, X(5)-$\beta^6$, X(5)-$\beta^4$, and X(5)-$\beta^2$), based on particular solutions of the geometrical Bohr Hamiltonian with harmonic potential in the $\gamma$ degree of freedom, and the interacting boson model (IBM) are explored. This work is the natural extension of the work presented in [1] for the E(5)-models. For that purpose, a quite general one- and two-body IBM Hamiltonian is used and a numerical fit to the different X(5)-models energies is performed, later on the obtained wave functions are used to calculate B(E2) transition rates. It is shown that within the IBM one can reproduce well the results for energies and B(E2) transition rates obtained with all these X(5)-models, although the agreement is not so impressive as for the E(5)-models. From the fitted IBM parameters the corresponding energy surface can be extracted and it is obtained that, surprisingly, only the X(5) case corresponds in the moderate large N limit to an energy surface very close to the one expected for a critical point, while the rest of models seat a little farther.Comment: Accepted in Physical Review

On the relation between E(5)−E(5)-models and the interacting boson model

The connections between the $E(5)-$models (the original E(5) using an infinite square well, $E(5)-\beta^4$, $E(5)-\beta^6$ and $E(5)-\beta^8$), based on particular solutions of the geometrical Bohr Hamiltonian with $\gamma$-unstable potentials, and the interacting boson model (IBM) are explored. For that purpose, the general IBM Hamiltonian for the $U(5)-O(6)$ transition line is used and a numerical fit to the different $E(5)-$models energies is performed, later on the obtained wavefunctions are used to calculate B(E2) transition rates. It is shown that within the IBM one can reproduce very well all these $E(5)-$models. The agreement is the best for $E(5)-\beta^4$ and reduces when passing through $E(5)-\beta^6$, $E(5)-\beta^8$ and E(5), where the worst agreement is obtained (although still very good for a restricted set of lowest lying states). The fitted IBM Hamiltonians correspond to energy surfaces close to those expected for the critical point. A phenomenon similar to the quasidynamical symmetry is observed

The nuclear and extended infrared emission of the Seyfert galaxy NGC 2992 and the interacting system Arp 245

We present subarcsecond resolution infrared (IR) imaging and mid-IR spectroscopic observations of the Seyfert 1.9 galaxy NGC 2992, obtained with the Gemini North Telescope and the Gran Telescopio CANARIAS (GTC). The N-band image reveals faint extended emission out to ~3 kpc, and the PAH features detected in the GTC/CanariCam 7.5-13 micron spectrum indicate that the bulk of this extended emission is dust heated by star formation. We also report arcsecond resolution MIR and far-IR imaging of the interacting system Arp 245, taken with the Spitzer Space Telescope and the Herschel Space Observatory. Using these data, we obtain nuclear fluxes using different methods and find that we can only recover the nuclear fluxes obtained from the subarcsecond data at 20-25 micron, where the AGN emission dominates. We fitted the nuclear IR spectral energy distribution of NGC 2992, including the GTC/CanariCam nuclear spectrum (~50 pc), with clumpy torus models. We then used the best-fitting torus model to decompose the Spitzer/IRS 5-30 spectrum (~630 pc) in AGN and starburst components, using different starburst templates. We find that, whereas at shorter mid-IR wavelengths the starburst component dominates (64% at 6 micron), the AGN component reaches 90% at 20 micron. We finally obtained dust masses, temperatures and star formation rates for the different components of the Arp 245 system and find similar values for NGC 2992 and NGC 2993. These measurements are within those reported for other interacting systems in the first stages of the interaction.Comment: 20 pages, 12 figures, accepted by MNRA

Finite-size scaling exponents in the interacting boson model

We investigate the finite-size scaling exponents for the critical point at the shape phase transition from U(5) (spherical) to O(6) (deformed $\gamma$-unstable) dynamical symmetries of the Interacting Boson Model, making use of the Holstein-Primakoff boson expansion and the continuous unitary transformation technique. We compute exactly the leading order correction to the ground state energy, the gap, the expectation value of the $d$-boson number in the ground state and the $E2$ transition probability from the ground state to the first excited state, and determine the corresponding finite-size scaling exponents.Comment: 4 pages, 3 figures, published versio

Phase diagram for a Cubic Consistent-Q Interacting Boson Model Hamiltonian: signs of triaxiality

An extension of the Consistent-Q formalism for the Interacting Boson Model that includes the cubic QxQxQ term is proposed. The potential energy surface for the cubic quadrupole interaction is explicitly calculated within the coherent state formalism using the complete chi-dependent expression for the quadrupole operator. The Q-cubic term is found to depend on the asymmetry deformation parameter gamma as a linear combination of cos(3gamma) and cos^2(3\gamma) terms, thereby allowing for triaxiality. The phase diagram of the model in the large N limit is explored, it is described the order of the phase transition surfaces that define the phase diagram, and moreover, the possible nuclear equilibrium shapes are established. It is found that, contrary to expectations, there is only a very tiny region of triaxiality in the model, and that the transition from prolate to oblate shapes is so fast that, in most cases, the onset of triaxiality might go unnoticed.Comment: 18 pages, 19 figure