arXiv subjects

Peter O. Hess

Publications and source records attributed to Peter O. Hess.

36 records · Page 2Linked to original sources

arXiv2015

Vacuum fluctuation inside a star and their consequences for neutron stars, a simple model

Applying semi-classical Quantum Mechanics, the vacuum fluctuations within a star are determined, assuming a constant mass density and applying a monopole approximation. It is found that the density for the vacuum fluctuations does not only depend linearly on the mass density, as assumed in a former publication, where neutron stars up to 6 solar masses were obtained. This is used to propose a simple model on the dependence of the dark energy to the mass density, as a function of the radial distance r. It is shown that stars with up to 200 solar masses can, in principle, be obtained. Though, we use a simple model, it shows that in the presence of vacuum fluctuations stars with large masses can be stabilized and probably stars up to any mass can exist, which usually are identified as black holes.

gr-qc↗

arXiv2014

A proposal of Quantization in flat space-time with a minimal length present

The 4-dimensional space-time is extended to pseudo-complex coordinates. Proposing the standard quantization rules in this extended space, the ones for the 4-dimensional sub-space acquire, as one solution, the commutation relations with non-commuting coordinates. This demonstrates that the algebraic extension keeps the simple structure of Quantum Mechanics, while it also introduces an effective quite involved structure in the 4-dimensional sub-space. The similarities to H. S. Snyder's work, a former proposal to include the effects of a minimal length, are exposed. The first steps to pseudo-complex Quantum Mechanics in 1-dimension are outlined, awaiting still the interpretation of some new emerging structures. As an example, two waves, out of phase by 90 degrees, are added which classically annihilate each other, while in the pseudo-complex description there is a non-zero amplitude.

gr-qc↗

arXiv2012

Experimental tests of pseudo-complex General Relativity

Based on previous publications exploring pseudo-complex General Relativity (pc-GR) we present a selection of observable consequences of pc-GR and possible ways to experimentally access them. Whenever possible we compare the results to Einstein's GR and differences are worked out in detail. We propose experimental tests to check the predictions of pc-GR for the orbital frequency of test particles, the gravitational redshift effect and the last stable orbit. We will show that the orbital frequency of test particles at a given radius in pc-GR is in general lower compared to standard GR. Also the effect of frame dragging is modified (weakened) in pc-GR. Concerning the gravitational redshift of a radiation emitting object we find that it is also lower in pc-GR than in standard GR. Eventually the classical concept of a last stable orbit has to be modified in pc-GR.

gr-qc↗

arXiv2010

The Robertson-Walker Metric in a Pseudo-Complex General Relativity

We investigate the consequences of the pseudo-complex General Relativity within a pseudo-complexified Roberston-Walker metric. A contribution to the energy-momentum tensor arises, which corresponds to a dark energy and may change with the radius of the universe, i.e., time. Only when the Hubble function $H$ does not change in time, the solution is consistent with a constant $Λ$.

gr-qc↗

arXiv2009

A Solvable Model for Many Quark Systems in QCD Hamiltonians

Motivated by a canonical, QCD Hamiltonian we propose an effective Hamiltonian to represent an arbitrary number of quarks in hadronic bags. The structure of the effective Hamiltonian is discussed and the BCS-type solutions that may represent constituent quarks are presented. The single particle orbitals are chosen as 3-dimensional harmonic oscillators and we discuss a class of exact solutions that can be obtained when a subset of single-particle basis states is restricted to include a certain number of orbital excitations. The general problem, which includes all possible orbital states, can also be solved by combining analytical and numerical methods.

nucl-th↗

arXiv2008

Pseudo-complex General Relativity

An extension of the theory of General Relativity is proposed, based on pseudo-complex space-time coordinates. The new theory corresponds to the introduction of two, in general different, metrics which are connected through specific conditions. A pseudo-complex Schwarzschild solution is constructed, which does not suffer any more by a singularity. The solution indicates a minimal radius for a heavy mass object. Consequences for the redshift and possible signatures for its observation are discussed.

gr-qc↗

arXiv2007

Pseudo-Complex Field Theory

A new formulation of field theory is presented, based on a pseudo-complex description. An extended group structure is introduced, implying a minimal scalar length, rendering the theory regularized a la Pauli-Villars. Cross sections are calculated for the scattering of an electron at an external Coulomb field and the Compton scattering. Deviations due to a smallest scalar length are determined. The theory also permits a modification of the minimal coupling scheme, resulting in a generalized dispersion relation. A shift of the Greisen-Zatsepin-Kuzmin-limit (GZK) of the cosmic ray spectrum is the consequence.

hep-th↗

arXiv2005

An exactly solvable limit of low energy QCD

Starting from the QCD Hamiltonian, we derive a schematic Hamiltonian for low energy quark dynamics with quarks restricted to the lowest s-level. The resulting eigenvalue problem can be solved analytically. Even though the Hamiltonian exhibits explicit chiral symmetry the severe restriction of the number of degrees of freedom breaks the pattern of chiral symmetry breaking for finite quark masses.

nucl-th↗

arXiv2004

Dimensional Reduction, Hard Thermal Loops and the Renormalization Group

We study the realization of dimensional reduction and the validity of the hard thermal loop expansion for lambda phi^4 theory at finite temperature, using an environmentally friendly finite-temperature renormalization group with a fiducial temperature as flow parameter. The one-loop renormalization group allows for a consistent description of the system at low and high temperatures, and in particular of the phase transition. The main results are that dimensional reduction applies, apart from a range of temperatures around the phase transition, at high temperatures (compared to the zero temperature mass) only for sufficiently small coupling constants, while the HTL expansion is valid below (and rather far from) the phase transition, and, again, at high temperatures only in the case of sufficiently small coupling constants. We emphasize that close to the critical temperature, physics is completely dominated by thermal fluctuations that are not resummed in the hard thermal loop approach and where universal quantities are independent of the parameters of the fundamental four-dimensional theory.

hep-th↗

arXiv2002

Selection rules in the double beta decay of deformed nuclei

The 2 nu double beta decay half-lives of six nuclei, whose decays were previously reported as theoretically forbidden, are calculated by including the pairing interaction, which mixes different occupations and opens up the possibility of the decay. All allowed channels for the 0 nu double beta decay are also computed. The estimated 2 nu double beta half-lives suggest that measurements in 244Pu may find positive signals, and that planned experiments would succeed in detecting the 2 nu double beta decay in 160Gd. Limits for the zero neutrino mode, in the analyzed deformed emitters, are predicted.

nucl-th↗

arXiv2002

Theoretical description of the double beta decay of 160Gd

The half-life of the 2 neutrino double-beta-decay of 160Gd, a process which was previously reported as theoretically forbidden, is estimated by including the pairing interaction, which mixes different occupations and opens channels for the decay. Explicit expressions are presented for the pairing mixing, and for the 2 nu and 0 nu double-beta-decay nuclear matrix elements in the present pseudo SU(3) approach. The estimated double-beta-decay half-lives suggest that the planned experiments would succeed in detecting the 2 nu double-beta-decay in 160Gd, and in putting competitive limits for the zero neutrino mode.

nucl-th↗

arXiv2001

Double beta decay in deformed nuclei

The pseudo SU(3) approach has been used to describe many low-lying rotational bands, as well as BE(2) and B(M1) intensities in rare earth and actinide nuclei, both with even-even and odd-mass numbers . The double beta half lives of some of these parent nuclei to the ground and excited states of the daughter ones were evaluated for the two and zero neutrino emitting modes using the pseudo SU(3) scheme. The predictions were in good agreement with the available experimental data for 150Nd and 238U. The double electron capture half-lives of 156Dy, 162Er and 168Yb were also studied using the same formalism. The first nuclei was found to be the best candidate for experimental detection, with a half-life of 10^24 yr to the first excited 0+ state in 156Gd. There are strong selection rules which restrict the two neutrino mode of the double beta decay in some other nuclei, including 160Gd. Experimental limits for the double beta decay of 160Gd have been reported . Recently it was argued that the strong cancellation of the 2nu mode in the double beta decay of 160Gd would suppress the background for the detection of the 0nu mode. In the present contribution we extend the previous research evaluating the double beta half lives of 160Gd using the pseudo SU(3) model. While the 2nu mode is forbidden when the most probable occupations are considered, states with different occupation numbers can be mixed through the pairing interaction. The amount of this mixing is evaluated using perturbation theory. The possibility of observing the double beta decay in 160Gd is discussed for both the 2nu and 0nu modes.

nucl-th↗

arXiv1997

QRPA and its extensions in a solvable model

An exactly solvable model is introduced, which is equivalent to the exact shell-model treatment of protons and neutrons in a single j-shell for Fermi-type excitations. Exact energies, quasiparticle numbers and double beta decay Fermi amplitudes are computed and compared with the results of both the standard quasiparticle random phase approximation (QRPA) and the renormalized one (RQRPA), and also with those corresponding to the hamiltonian in the quasiparticle basis (qp). A zero excitation energy state is found in the exact case, occuring at a value of the residual particle-particle interaction at which the QRPA collapse. The RQRPA and the qp solutions do not include this zero-energy eigenvalue in their spectra, probably due to spurious correlations.

nucl-th↗

arXiv1996

Single- and double-beta decay Fermi-transitions in an exactly solvable model

An exactly solvable model suitable for the description of single and double-beta decay processes of the Fermi-type is introduced. The model is equivalent to the exact shell-model treatment of protons and neutrons in a single j-shell. Exact eigenvalues and eigenvectors are compared to those corresponding to the hamiltonian in the quasiparticle basis (qp) and with the results of both the standard quasiparticle random phase approximation (QRPA) and the renormalized one (RQRPA). The role of the scattering term of the quasiparticle hamiltonian is analyzed. The presence of an exact eigenstate with zero energy is shown to be related to the collapse of the QRPA. The RQRPA and the qp solutions do not include this zero-energy eigenvalue in their spectra, probably due to spurious correlations. The meaning of this result in terms of symmetries is presented.

nucl-th↗

arXiv1996

Double beta decay and the proton-neutron residual interaction

The validity of the pn-QRPA and -RQRPA descriptions of double beta decay transition amplitudes is analyzed by using an exactly solvable model. It is shown that the collapse of the QRPA is physically meaningful and that it is associated with the appearance of a state with zero energy in the spectrum. It is shown that in the RQRPA this particular feature is not present and that this approach leads to finite but otherwise spurious results for the double beta decay transition amplitudes near the point of collapse.

nucl-th↗

arXiv1996

Renormalized QRPA and double beta decay: a critical analysis of double Fermi transitions

The proton-neutron monopole Lipkin model, which exhibits some properties which are relevant for those double beta decay ($ββ$) transitions mediated by the Fermi matrix elements, is solved exactly in the proton-neutron two-quasiparticle space. The exact results are compared with the ones obtained by using the Quasiparticle Random Phase (QRPA) and renormalized QRPA (RQRPA) approaches. It is shown that the RQRPA violates the Ikeda Sum Rule and that this violation may be common to any extension of the QRPA where scattering terms are neglected in the participant one-body operators as well as in the Hamiltonian. This finding underlines the need of additional developments before the RQRPA could be adopted as a reliable tool to compute $ββ$ processes.

nucl-th↗

arXiv1995

Double beta decay to excited states in Nd150

The pseudo SU(3) model is used to study the double beta decay of Nd150 to the ground and excited states of Sm150 . Low lying collective excitations of Sm150 and its BE(2) intensities are well reproduced. Expressions for the two neutrino double beta decay to excited states are developed and used to describe the decay of Nd150 . The existence of selection rules which strongly restrict the decay is discussed.

nucl-th↗

arXiv1994

Pseudo SU(3) Model and Abnormal Parity States

The most important features of the pseudo SU(3) model are reviewed. This description of heavy deformed nuclei is based on pseudo spin symmetry, and is able to correctly predict the collective spectra and their transition amplitudes, using appropriate effective charges. It also gives a very good description of the exotic double beta decay, a hard test of any nuclear model. The simplest pseudo SU(3) assumptions describe nucleons in the abnormal parity states as having seniority zero. This idea is very useful as a mathematical simplification, and is also able to give a nice description of the backbending phenomena, but has been challenged in a recent study about effective charges and $BE2(0^+_1 \rightarrow 2^+_1)$ systematics. We carefully checked this statement and conclude that the seniority zero approach is a formal way of assign abnormal parity nucleons a passive role. The contribution of the abnormal parity nucleons to the nuclear quadrupole moments is finite but only a fraction of their asymptotic Nilsson values.

nucl-th↗