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Alberto Escuderos

Publications and source records attributed to Alberto Escuderos.

13 recordsLinked to original sources
arXiv2017

Equally Spaced Levels with T=1 two-body Matrix elements

If one examines two-body matrix elements from experiment one notices that not only J=0 T=1 lies low but also J=1T=0 and J=J_{max} =2j T=0. It is sometimes thought that one needs both T=1 and T=0 two-body matrix elements to get equally spaced spectra of even I states i.e. vibraitonal spectra. We here attempt to get equally spaced levels with only those that have T=1 (even J).As an example we perform single-j calculations (f_{7/2}) in ^{44} T and ^{46} Ti. We then shift gears and decide to play around with the input two particle matrix, elements (not worrying about experiment) to generate interesting spectra e.g. rotaional spectra with and then without T=0 two-body matrix element. Of special interest is a new partial dynamical symmetry found when the "123", the "1234" etc.,interactions are used.

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arXiv2016

Degeneracies with the Q.Q interaction in a single j shell

Previously [1] it was shown that for a configuration of 2 protons and 2 neutrons in the g_{9/2}shell there is a certain degeneracy that occurs when the quadrupole-quadrupole interaction (Q.Q) is used to to obtain the wave functions.. We here show 3 other examples of such degenerate pairs, all, as before, involving T=0 and T=2 states. . More important we discuss an unusual peculiarity of the original example. Also we point out that degeneracies can be confusing and steps can be taken to remove them.

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arXiv2016

Partial Conservation Law in a Schematic Single j Shell Model

We report the discovery of a partial conservation law obeyed by a schematic Hamiltonian of two protons and two neutrons in a j shell. In our Hamiltonian the interaction matrix element of two nucleons with combined angular momentum J is linear in J for even J and constant for odd J. It turns out that in some stationary states the sum J_p + J_n of the angular momenta J_p and J_n of the proton and neutron pairs is conserved. The energies of these states are given by a linear function of J_p + J_n. The systematics of their occurrence is described and explained.

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arXiv2013

The large j limit for certain 9-j symbols-power law behaviour

In a previous work certain unitary9-j symbols were shown to go asymptotically to zero in the large j limit. In this work we examine this inmore detail. We find an approximate power law for the behaviour of ccertain U9-j's in the large j limit and exponential decreased for others.

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arXiv2013

Isobaric analog states in the f_{7/2} and g_{9/2} shells

Calculations are performed for energies of isobaric analog states with isospins T=2 and T=3 in regions where they have been found experimentally e.g. f-p shell, and regions where they have not yet been found e.g. g_{9/2} near Z=50,N=50. We consider two approaches--one using binding energy formulas and Coulomb energies contained therein and the other using shell model calculations. It is noted that some (but not all) calculations yield very low excitation energies for the J=0^{+} T=2 isobaric analog state in ^{96} Ag.

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arXiv2013

Isobaric Analog State in ^{96} Ag

Preiviously, in a single j-shell calculation (j=g_{9/2}), we obtained the excitation energy of the T=2 J=0+ isobaric analog state in ^{96} Ag to be a bit below 1 MeV relative to the J=8+ T=1 ground state . We here use binding energy data and Coulomb energy estimates to obtain this same excitation energy and to see if the 2 approaches are consistent.

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arXiv2012

The (2j-1) rule with other interactions

We recently formulated a rule for isomeric states for a system of 4 nucleons with isospin T=1, namely that if the nucleons are in a single j shell then states with angular momenta J=2 and J=(2j-1) are either isomeric or ground states [ze12]. To show that this is a robust result, we here consider a new interaction from the literature that was used to discuss even-even and odd-even nuclei. We here apply it to an odd-odd nucleus.

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arXiv2012

Single j-shell studies of cross-conjugate nuclei and isomerism

It is noted that in a calculation with 4 nucleons with isospin 1 in a single j shell (f_{7/2}, g_{9/2}, h_{11/2}) the state with median angular momentum J = (J_{max}+1)/2 lies very low in energy becoming either an isomeric state or a ground state. Also states with J = J_{max} are isomeric for the orbits g_{9/2} and h_{11/2}. Comparisons with experiment are made. A hybrid mixture of shell model and rotational model arguments are used to explain the (J_{max} +1)/2 rule.

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arXiv2010

Contributions of different neutron pairs in different approaches for neutrinoless double beta decay

The methods used till now to calculate the neutrinoless double beta decay matrix elements are: the Quasiparticle Random Phase Approximation (QRPA), the Shell Model (SM), the angular momentum projected Hartee-Fock-Bogoliubov approach (HFB) and the Interacting Boson Model (IBM). The different approaches are compared specifically concerning the the angular momenta and parities of the neutron pairs, which are changed into two protons by the $0νββ$ decay. The QRPA and SM involve about the same angular momentum and parity neutron pairs, while the HFB is restricted to $0^{+}, 2^{+}, 4^{+}, ...$, and IBM to $0^{+}$ and $2^{+}$ nucleon pairs. The differences in the seniority contributions for the QRPA and the SM are discussed.

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arXiv2006

New Relations for Coefficients of Fractional Parentage--the Redmond Recursion Formula with Seniority

We find a relationship between coefficients of fractional parentage (cfp) obtained on the one hand from the principal parent method and on the other hand from a seniority classification. We apply this to the Redmond recursion formula which relates $n \to n+1$ cfp's to $n-1 \to n$ cfp's where the principal parent classification is used. We transform this to the seniority scheme. Our formula differs from the Redmond formula inasmuch as we have a sum over the possible seniorities for the $n \to n+1$ cfp's, whereas Redmond has only one term.

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arXiv2005

Unfolding the Effects of the T=0 and T=1 Parts of the Two-Body Interaction on Nuclear Collectivity in the f-p Shell

Calculations of the spectra of various even-even nuclei in the fp shell ({44}Ti, {46}Ti, {48}Ti, {48}Cr and {50}Cr) are performed with two sets of two-body interaction matrix elements. The first set consists of the matrix elements of the FPD6 interaction. The second set has the same T=1 two-body matrix elements as the FPD6 interaction, but all the T=0 two-body matrix elements are set equal to zero (T0FPD6). Surprisingly, the T0FPD6 interaction gives a semi-reasonable spectrum (or else this method would make no sense). A consistent feature for even-even nuclei, e.g. {44,46,48}Ti and {48,50}Cr, is that the reintroduction of T=0 matrix elements makes the spectrum look more rotational than when the T=0 matrix elements are set equal to zero. A common characteristic of the results is that, for high spin states, the excitation energies are too high for the full FPD6 interaction and too low for T0FPD6, as compared with experiment. The odd-even nucleus {43}Ti and the odd-odd nucleus {46}V are also discussed. For {43}Sc the T=0 matrix elements are responsible for staggering of the high spin states. In general, but not always, the inclusion of T=0 two-body matrix elements enhances the B(E2) rates.

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arXiv2004

Companion problems in quasispin and isospin

We note that the same mathematical results apply to problems involving quasispin and isospin, but the problems per se are different. In the quasispin case, one deals with a system of identical fermions (e.g. neutrons) and address the problem of how many seniority conserving interactions there are. In the isospin case, one deals with a system of both neutrons and protons and the problem in question is the number of neutron-proton pairs with a given total angular momentum. Other companion problems are also discussed.

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