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N. K. Nielsen

Publications and source records attributed to N. K. Nielsen.

12 recordsLinked to original sources
arXiv2014

Removing the gauge parameter dependence of the effective potential by a field redefinition

The gauge parameter dependence of the effective potential is determined by partial differential equations involving also the Higgs boson field expectation value. Solving these equations by the method of characteristics leads to complete elimination of the gauge parameter dependence of the effective potential. The construction is carried out in the case of the standard model of electroweak unification for the renormalization group improved effective potential up to the next-leading logarithmic order.

hep-ph↗
arXiv2014

Higgs boson decay into two photons in an electromagnetic background

The amplitude for Higgs boson decay into two photons in a homogeneous and time-independent magnetic field is investigated by proper-time regularization in a gauge invariant manner and is found to be singular at large field values. The singularity is caused by the component of the charged vector boson field that is tachyonic in a strong magnetic field. Also tools for the computation of the amplitude in a more general electromagnetic background are developed.

hep-ph↗
arXiv2014

The Einstein-Maxwell system, Ward identities, and the Vilkovisky construction

The gauge fixing dependence of the one-loop effective action of quantum gravity in the proper-time representation is investigated for a space of arbitrary curvature, and the investigation is extended to Maxwell-Einstein theory. The construction of Vilkovisky and DeWitt for removal of this depence is then considered in general gauges, and it is shown that nontrivial criteria arising from a Ward identity of the theory must be obeyed by the regularization scheme, if the construction is to remove the gauge dependence of quadratic and quartic divergences. The results apply also to non-Abelian gauge theories; they are used to address the question of gauge dependence of asymptotic freedom arising through internal graviton lines at one-loop order as suggested by Robinson and Wilczek.

hep-th↗
arXiv2005

Instanton constraints and renormalization

The renormalization is investigated of one-loop quantum fluctuations around a constrained instanton in $ϕ^4$-theory with negative coupling. It is found that the constraint should be renormalized also. This indicates that in general only renormalizable constraints are permitted.

hep-th↗
arXiv2005

Instanton constraints in supersymmetric gauge theories I. Supersymmetric QCD

A previous analysis of possible constraints of Yang-Mills instantons in the presence of spontaneous symmetry breaking is extended to supersymmetric QCD. It is again found that a constraint is necessary for the gauge field in second and fourth order of the gauge breaking parameter v. While the supersymmetric zero mode is well behaved to all orders, the lifted superconformal and quark zero modes show nonpermissible behaviour, but only at first order in v.

hep-th↗
arXiv2004

On the Origin of Kaluza's Idea of Unification

We argue that the starting point of Kaluza's idea of unifying electrodynamics and gravity was the analogy between gravitation and electromagnetism which was pointed out by Einstein and Thirring. It seems that Kaluza's attention was turned to this point by the three papers on the Lense-Thirring effect and the analogy between gravitation and electromagnetism which were published a short time before Kaluza's paper was submitted. We provide here an English translation of the third of these papers.

physics.hist-ph↗
arXiv2000

Alternative approaches to the Casalbuoni-Brink-Schwarz Superparticle

Wigner's method of induced representations is applied to the N=1 super-Poincare group, and by using a state corresponding to the basic vector of the little group as a Clifford vacuum we show that the spin operator of a supersymmetric point particle obeys Wigner's constraints. As dynamical variables for the particle we use canonical coordinates on the symmetry group manifold. The physical phase space is then constructed using a vielbein formalism. We find that the Casalbuoni-Brink-Schwarz superparticle appears as a special case of our general construction. Finally, the theory is reformulated as a gauge theory where the gauge freedom corresponds to the choice of spin constraints or, equivalently, the free choice of relativistic center of mass. In a special case the gauge symmetry reduces to the well known kappa-symmetry.

hep-th↗
arXiv1999

Explicit construction of constrained instantons

Instantons in massless theories do not carry over to massive theories due to Derrick's theorem. This theorem can, however, be circumvented, if a constraint that restricts the scale of the instanton is imposed on the theory. Constrained instantons are considered in four dimensions in phi^4 theory and SU(2) Yang-Mills-Higgs theory. In each of these theories a calculational sceme is set up and solved in the lowest few orders in the mass parameter in such a way that the need for a constraint is exhibited clearly. Constrained instantons are shown to exist as finite action solutions of the field equations with exponential fall off only for specific constraints that are unique in lowest order in the mass parameter in question.

hep-th↗
arXiv1997

Physical Interpretation of Cylindrically Symmetric Static Gravitational Fields

The explicit relationship is determined between the interior properties of a static cylindrical matter distribution and the metric of the exterior space-time according to Einstein gravity for space-time dimensionality larger or equal to four. This is achieved through use of a coordinate system isotropic in the transverse coordinates. As a corollary, similar results are obtained for a spherical matter distribution in Brans-Dicke gravity for dimensions larger than or equal to three. The approach used here leads to consistency conditions for those parameters characterizing the exterior metric. It is shown that these conditions are equivalent to the requirement of hydrostatic equilibrium of the matter distribution (generalized Oppenheimer-Volkoff equations). These conditions lead to a consistent Newtonian limit where pressures and the gravitational constant go to zero at the same rate.

gr-qc↗
arXiv1997

Gauge theory of a massive relativistic spinning point particle

A massive relativistic spinning point particle in any number of dimensions has in a previous article been shown to be described by first class constraints, which define a gauge theory. In the present paper we find the corresponding finite gauge transformations. By comparing the integrated gauge transformations to transformation equations found by Pryce, we conclude that the selection of gauge corresponds to selection of the relativistic center of mass frame in the model of Pryce, where a spinning particle is considered a composite object. The Lorentz group is identified as the gauge group, and as gauge field we identify the relativistic angular velocity. We also show that an analogous physical interpretation is possible for the relativistic spherical top of Hanson and Regge.

hep-th↗
arXiv1995

The relativistic top: An application of the BFV quantization procedure for systems with degenerate constraints

The physical phase space of the relativistic top, as defined by Hanson and Regge, is expressed in terms of canonical coordinates of the Poincaré group manifold. The system is described in the Hamiltonian formalism by the mass shell condition and constraints that reduce the number of spin degrees of freedom. The constraints are second class and are modified into a set of first class constraints by adding combinations of gauge fixing functions. The Batalin-Fradkin-Vilkovisky (BFV) method is then applied to quantize the system in the path integral formalism in Hamiltonian form. It is finally shown that different gauge choices produce different equivalent forms of the constraints.

hep-th↗