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We compute the binding energy of neutron-rich oxygen isotopes and employ the coupled-cluster method and chiral nucleon-nucleon interactions at next-to-next-to-next-to-leading order with two different cutoffs. We obtain rather well-converged results in model spaces consisting of up to 21 oscillator shells. For interactions with a momentum cutoff of 500 MeV, we find that 28O is stable with respect to 24O, while calculations with a momentum cutoff of 600 MeV result in a slightly unbound 28O. The theoretical error estimates due to the omission of the three-nucleon forces and the truncation of excitations beyond three-particle-three-hole clusters indicate that the stability of 28O cannot be ruled out from ab-initio calculations, and that three-nucleon forces and continuum effects play the dominant role in deciding this question., Comment: 5 pages + eps, 3 figures

The single-particle spectral function of 56Ni has been computed within the framework of self-consistent Green's functions theory. The Faddeev random phase approximation method and the G-matrix technique are used to account for the effects of long- and short-range physics on the spectral distribution. Large scale calculations have been performed in spaces including up to ten oscillator shells. The chiral N3LO interaction is used together with a monopole correction that accounts for eventual missing three-nucleon forces. The single-particle energies associated with nucleon transfer to valence 1p0f orbits are found to be almost converged with respect to both the size of the model space and the oscillator frequency. The results support that 56Ni is a good doubly magic nucleus. The absolute spectroscopic factors to the valence states on A=55,57 are also obtained. For the transition between the ground states of 57Ni and 56Ni, the calculations nicely agree with heavy-ion knockout experiments., Comment: Minor comments and references added, accepted for publication on Phys. Rev. C

We compute the binding energies, radii, and densities for selected medium-mass nuclei within coupled-cluster theory and employ the "bare" chiral nucleon-nucleon interaction at order N3LO. We find rather well-converged results in model spaces consisting of 15 oscillator shells, and the doubly magic nuclei 40Ca, 48Ca, and the exotic 48Ni are underbound by about 1 MeV per nucleon within the CCSD approximation. The binding-energy difference between the mirror nuclei 48Ca and 48Ni is close to theoretical mass table evaluations. Our computation of the one-body density matrices and the corresponding natural orbitals and occupation numbers provides a first step to a microscopic foundation of the nuclear shell model., Comment: 5 pages, 5 figures

In a recent Letter [Phys. Rev. Lett. 99, 092501 (2007)], Roth and Navratil present an importance-truncation scheme for the no-core shell model. The authors claim that their truncation scheme leads to converged results for the ground state of 40-Ca. We believe that this conclusion cannot be drawn from the results presented in the Letter. Furthermore, the claimed convergence is at variance with expectations of many-body theory. In particular, coupled-cluster calculations indicate that a significant fraction of the correlation energy is missing., Comment: 1 page, comment on arXiv:0705.4069 (PRL 99, 092501 (2007))

We present ab-initio calculations for 3H, 4He, 16O, and 40Ca based on two-nucleon low-momentum interactions Vlowk within coupled-cluster theory. For 3H and 4He, our results are within 70 keV and 10 keV of the corresponding Faddeev and Faddeev-Yakubovsky energies. We study in detail the convergence with respect to the size of the model space and the single-particle basis. For the heavier nuclei, we report practically converged binding energies and compare with other approaches., Comment: 8 pages, 13 figures

We show in detail how the Jordan-Wigner transformation can be used to simulate any fermionic many-body Hamiltonian on a quantum computer. We develop an algorithm based on appropriate qubit gates that takes a general fermionic Hamiltonian, written as products of a given number of creation and annihilation operators, as input. To demonstrate the applicability of the algorithm, we calculate eigenvalues and eigenvectors of two model Hamiltonians, the well-known Hubbard model and a generalized pairing Hamiltonian. Extensions to other systems are discussed., Comment: 16 pages, 10 figures, revtex style

The development of new techniques to quantitatively measure gene expression in cells has shed light on a number of systems that display oscillations in protein concentration. Here we review the different mechanisms which can produce oscillations in gene expression or protein concentration, using a framework of simple mathematical models. We focus on three eukaryotic genetic regulatory networks which show "ultradian" oscillations, with time period of the order of hours, and involve, respectively, proteins important for development (Hes1), apoptosis (p53) and immune response (NFkB). We argue that underlying all three is a common design consisting of a negative feedback loop with time delay which is responsible for the oscillatory behaviour.

Rare isotope beams of neutron-deficient $^{106,108,110}$Sn nuclei from the fragmentation of $^{124}$Xe were employed in an intermediate-energy Coulomb excitation experiment yielding $B(E2, 0^+_1 \to 2^+_1)$ transition strengths. The results indicate that these $B(E2,0^+_1 \to 2^+_1)$ values are much larger than predicted by current state-of-the-art shell model calculations. This discrepancy can be explained if protons from within the Z = 50 shell are contributing to the structure of low-energy excited states in this region. Such contributions imply a breaking of the doubly-magic $^{100}$Sn core in the light Sn isotopes., Comment: 4 pages, 4 figures

We develop ab-initio coupled-cluster theory to describe resonant and weakly bound states along the neutron drip line. We compute the ground states of the helium chain 3-10He within coupled-cluster theory in singles and doubles (CCSD) approximation. We employ a spherical Gamow-Hartree-Fock basis generated from the low-momentum N3LO nucleon-nucleon interaction. This basis treats bound, resonant, and continuum states on equal footing, and is therefore optimal for the description of properties of drip line nuclei where continuum features play an essential role. Within this formalism, we present an ab-initio calculation of energies and decay widths of unstable nuclei starting from realistic interactions., Comment: 4 pages, revtex4

We present results from large-scale shell-model calculations of even and odd tin isotopes from 134Sn to 142}Sn with a shell-model space defined by the 1f7/2,2p3/2,0h9/2,2p1/2,1f5/2,0i13/2 single-particle orbits. An effective two-body interaction based on modern nucleon-nucleon interactions is employed. The shell-model results are in turn analyzed for their pairing content using a generalized seniority approach. Our results indicate that a pairing-model picture captures a great deal of the structure and the correlations of the lowest lying states for even and odd isotopes., Comment: 7 pages, revtex latex style, submitted to PRC

The surface structure of Bi(110) has been investigated by low-energy electron diffraction (LEED) intensity analysis and by first-principles calculations. Diffraction patterns at a sample temperature of 110 K and normal incidence reveal a bulk truncated (1$\times$1) surface without indication of any structural reconstruction despite the presence of dangling bonds on the surface layer. Good agreement is obtained between the calculated and measured diffraction intensities for this complex, low-symmetry surface containing only one mirror-plane symmetry element. No significant interlayer spacing relaxations are found. The Debye temperature for the surface layer is found to be lower than in the bulk, which is indicative of larger vibrational atomic amplitudes at the surface. Meanwhile, the second layer shows a Debye temperature close to the bulk value. The experimental results for the relaxations agree well with those of our first-principles calculation.

In the context of scalar-tensor models of dark energy and inflation, the dynamics of vacuum scalar-tensor cosmology are analysed without specifying the coupling function or the scalar field potential. A conformal transformation to the Einstein frame is used and the dynamics of general relativity with a minimally coupled scalar field are derived for a generic potential. It is shown that the dynamics are non-chaotic, thus settling an existing debate., Comment: 20 pages, LaTeX, to appear in Class. Quantum Grav

We present a new and efficient method to obtain a Gamow shell-model basis and matrix elements generated by realistic nucleon-nucleon interactions. We derive a self-consistent Hartree-Fock potential from the renormalized N3LO interaction model. The corresponding Gamow one-body eigenstates are generated in a plane wave basis in order to build a Gamow shell-model set of basis states for the closed shell nuclei 4He and 16O. We address also the problem of representing a realistic nucleon-nucleon interaction in a two-particle Berggren basis in the laboratory frame. To achieve this, an expansion of matrix elements of the residual nucleon-nucleon interaction in a finite set of harmonic oscillator wave functions is used. We show that all loosely bound and narrow resonant states converge surprisingly fast. Even broad resonances in these two-particle valence systems converge within a reasonable number of harmonic oscillator functions. Examples of 6He and 18O Gamow shell-model calculations using 4He and 16}O as closed shell cores are presented. This procedure allows Gamow shell-model calculations to be performed with all realistic nucleon-nucleon interactions and with either momentum or position space representations for the Gamow basis. The possibility to remove the center of mass spuriosity of Gamow shell-model nuclear states with this method is also discussed. Perspectives for nuclear structure calculations of dripline nuclei are outlined., Comment: 17 pages, revtex. Revised manuscript. Physical Review C, in press

The inverse statistics is the distribution of waiting times needed to achieve a predefined level of return obtained from (detrended) historic asset prices \cite{optihori,gainloss}. Such a distribution typically goes through a maximum at a time coined the {\em optimal investment horizon}, $\tau^*_\rho$, which defines the most likely waiting time for obtaining a given return $\rho$. By considering equal positive and negative levels of return, we reported in \cite{gainloss} on a quantitative gain/loss asymmetry most pronounced for short horizons. In the present paper, the inverse statistics for 2/3 of the individual stocks presently in the DJIA is investigated. We show that this gain/loss asymmetry established for the DJIA surprisingly is {\em not} present in the time series of the individual stocks nor their average. This observation points towards some kind of collective movement of the stocks of the index (synchronization)., Comment: Subm. to Physica A as Conference Proceedings of Econophysics Colloquium, ANU Canberra, 13-17 Nov. 2005. 6 pages including figures

In recent publications, the authors have considered inverse statistics of the Dow Jones Industrial Averaged (DJIA) [1-3]. Specifically, we argued that the natural candidate for such statistics is the investment horizons distribution. This is the distribution of waiting times needed to achieve a predefined level of return obtained from detrended historic asset prices. Such a distribution typically goes through a maximum at a time coined the {\em optimal investment horizon}, $\tau^*_\rho$, which defines the most likely waiting time for obtaining a given return $\rho$. By considering equal positive and negative levels of return, we reported in [2,3] on a quantitative gain/loss asymmetry most pronounced for short horizons. In the present paper, this gain/loss asymmetry is re-visited for 2/3 of the individual stocks presently in the DJIA. We show that this gain/loss asymmetry established for the DJIA surprisingly is {\em not} present in the time series of the individual stocks. The most reasonable explanation for this fact is that the gain/loss asymmetry observed in the DJIA as well as in the SP500 and Nasdaq are due to movements in the market as a whole, {\it i.e.}, cooperative cascade processes (or ``synchronization'') which disappear in the inverse statistics of the individual stocks., Comment: Revtex 13 pages, including 15 figures

We report calculations for electronic ground states of parabolically confined quantum dots for up to 30 electrons based on the quantum Monte Carlo method. Effects of the electron-electron interaction and the response to a magnetic field are exposed. The wavefunctions and the ground state energies are compared with purely classical calculations performed with a comprehensive Molecular Dynamics code. For the chosen well parameters a close correspondence in the overall shape of electron density distribution is found even for small number of electrons, while the detailed radial distributions show the effects of Pauli principle in the quantal case., Comment: 6 pages, submitted to PRB

We briefly discuss recent experiments on quantum information processing using trapped ions at NIST. A central theme of this work has been to increase our capabilities in terms of quantum computing protocols, but we have also applied the same concepts to improved metrology, particularly in the area of frequency standards and atomic clocks. Such work may eventually shed light on more fundamental issues, such as the quantum measurement problem., Comment: Proceedings of the International Conference on Laser Spectroscopy (ICOLS), 10 pages, 5 figures

We study the ground and low-lying excited states of O-15, O-17, N-15, and F-17 using modern two-body nucleon-nucleon interactions and the suitably designed variants of the ab initio equation-of-motion coupled-cluster theory aimed at an accurate description of systems with valence particles and holes. A number of properties of O-15, O-17, N-15, and F-17, including ways the energies of ground and excited states of valence systems around O-16 change as functions of the number of nucleons, are correctly reproduced by the equation-of-motion coupled-cluster calculations. Within a harmonic oscillator basis and large effective model spaces, our results are converged for the chosen two-body Hamiltonians. Thus, all disagreements with experiment are, most likely, due to the degrees of freedom such as three-body interactions not accounted for in our effective two-body Hamiltonians. In particular, the calculated binding energies of O-15/N-15 and O-17/F-17 enable us to rationalize the discrepancy between the experimental and recently published [Phys. Rev. Lett. 94, 212501 (2005)] equation-of-motion coupled-cluster excitation energies for the Jpi=3- state of O-16. The results demonstrate the feasibility of the equation-of-motion coupled-cluster methods to deal with valence systems around closed-shell nuclei and to provide precise results for systems beyond A=16.

The $g$ factor of the $4_1^+$ state in $^{68}$Zn has been remeasured with improved energy resolution of the detectors used. The value obtained is consistent with the previous result of a negative $g$ factor thus confirming the dominant $0g_{9/2}$ neutron nature of the $4_1^+$ state. In addition, the accuracy of the $g$ factors of the $2_1^+$, $2_2^+$ and $3_1^-$ states has been improved an d their lifetimes were well reproduced. New large-scale shell model calculations based on a $^{56}$Ni core and an $0f_{5/2}1pg_{9/2}$ model space yield a theoretical value, $g(4_1^+) = +0.008$. Although the calculated value is small, it cannot fully explain the experimental value, $g(4_1^+) = -0.37(17)$. The magnitude of the deduced B(E2) of the $4_1^+$ and $2_1^+$ transition is, however, rather well described. These results demonstrate again the importance of $g$ factor measurements for nuclear structure determination s due to their specific sensitivity to detailed proton and neutron components in the nuclear wave functions., Comment: 7 pages, 3 figs, submitted to PLB

During the last decade we have witnessed an impressive development in so-called interpreted languages and computational environments such as Maple, Mathematica, IDL, Matlab etc. Problems which until recently were typically solved on mainframe machines and written in computing languages such as Fortran or C/C++, can now easily be solved on standard PCs with the bonus of immediate visualizations of the results. In our undergraduate programs an often posed question is how to incorporate and exploit efficiently these advances in the standard physics and mathematics curriculum, without detracting the attention from the classical and basic theoretical and experimental topics to be covered. Furthermore, if students are trained to use such tools at early stages in their education, do such tools really enhance and improve the learning environment? And, perhaps even more important, does it lead to a better physics understanding? Here we present one possible approach, where computational topics are gradually baked into our undergraduate curriculum in Mathematics and Physics, Astronomy and Meteorology. We focus on training our students to use general programming tools in solving physics problems, in addition to the classical analytic problems. By this approach, the students gain an expertise that they can build upon in their future studies and careers. We use mainly Java, Matlab and Maple as computational environments. Our students are now capable of handling at an early stage in their education more realistic physics problems than before. We believe firmly that, in addition to educating modern scientists, this promotes a better physics understanding for a majority of the students., Comment: Talk by Arnt Inge Vistnes at MPTL 9, 9th Workshop on Multimedia in Physics Teaching and Learning, Graz, Austria 9-11 September 2004. 7 pages

In this work we compare the results of the Gross-Pitaevskii and modified Gross-Pitaevskii equations with ab initio variational Monte Carlo calculations for Bose-Einstein condensates of atoms in axially symmetric traps. We examine both the ground state and excited states having a vortex line along the z-axis at high values of the gas parameter and demonstrate an excellent agreement between the modified Gross-Pitaevskii and ab initio Monte Carlo methods, both for the ground and vortex states., Comment: To appear in Phys Rev A 71

We report converged results for the ground and excited states and matter density of 16-O using realistic two-body nucleon-nucleon interactions and coupled-cluster methods and formalism developed in quantum chemistry. Most of the binding is obtained with the coupled-cluster singles and doubles approach. Additional binding due to three-body clusters (triples) is minimal. The coupled-cluster method with singles and doubles provides a good description of the matter density, charge radius, charge form factor, and excited states of a 1-particle-1-hole nature, but it cannot describe the first excited 0+ state. Incorporation of triples has no effect on the latter finding., Comment: 4 pages 2 figures

Development of neutron-rich radioactive beams at the HRIBF facility has stimulated experimental and theoretical activity in heavy Sn and Te isotopes. Recently, the g-factor of the first 2$^+$ state in $^{132}$Te has been measured. We report here new shell-model calculation of magnetic moments for selected Sn and Te isotopes. The residual interaction is based on the CD-Bonn renormalized $ G $-matrix. Single-particle spin and orbital effective g-factors are evaluated microscopically including core polarization and meson exchange currents effects., Comment: 7 pages, revtex4, submitted to PRC

We propose a scheme for extracting an effective three-body interaction originating from a two-nucleon interaction. This is based on the Q-box method of Kuo and collaborators, where folded diagrams are obtained by differentiating a sum of non-folded diagrams with respect to the starting energy. To gain insight we have studied several examples using the Lipkin model where the perturbative approach can be compared with exact results. Numerically the three-body interactions can be significant and in a matrix example good accuracy was not obtained simultaneously for both eigenvalues with two-body interactions alone., Comment: 9 pages, Revtex4, 7 figs, submitted to PRC