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H. R. Christiansen

Publications and source records attributed to H. R. Christiansen.

35 records · Page 2Linked to original sources
arXiv2010

Exact solutions for a Maxwell-Kalb-Ramond action with dilaton: Localization of massless and massive modes in a sine-Gordon brane-world

We analytically find the exact propagation modes of the electromagnetic and the Kalb-Ramond fields together in a five-dimensional curved space-time. The existence and localization of gauge particles into our four-dimensional world (4D) is studied in detail on a brane-world scenario in which two gauge fields interact with a dilaton and a gravitational background. The coupling to the dilaton is different in each case causing the splitting between both gauge spectra. The gauge field zero-modes and an infinite tower of Kaluza-Klein massive states are analytically obtained. Relevant conditions on the dilaton coupling constant are found in order to identify with precision every finite tensor and vector eigenstate in the theory. An exact quantization condition on the whole mass spectrum, depending on the dilaton coupling constant and the bulk Planck mass, is inherited from the extra-dimension. This allows finding an exact rule to prevent tachyons in the theory and, by the same token, predicting a possible Kalb-Ramond tensor zero-mode in 4D world. We also show that KK massive-modes contributions onto 4D physics are strongly suppressed.

hep-th↗
arXiv2002

Noncommutative Quantum Mechanics and rotating frames

We study the effect of noncommutativity of space on the physics of a quantum interferometer located in a rotating disk in a gauge field background. To this end, we develop a path-integral approach which allows defining an effective action from which relevant physical quantities can be computed as in the usual commutative case. For the specific case of a constant magnetic field, we are able to compute, exactly, the noncommutative Lagrangian and the associated shift on the interference pattern for any value of $θ$.

hep-th↗
arXiv2001

Electron-electron bound states in parity-preserving QED_3 applied to high-T_c cuprate superconductors

We consider a parity-preserving QED_3 model with spontaneous breaking of the gauge symmetry as a framework for the evaluation of the electron-electron interaction potential underlying high-T_c superconductivity. The fact that the resulting potential, -C_s K_{0}(Mr), is non-confining and ``weak'' (in the sense of Kato) strongly suggests the mechanism of pair-condensation. This potential, compatible with an s-wave order parameter, is then applied to the Schrödinger equation for the sake of numerical calculations, thereby enforcing the existence of bound states. The results worked out by means of our theoretical framework are checked by considering a number of phenomenological data extracted from different copper oxide superconductors. The agreement may motivate a deeper analysis of our model viewing an application to quasi-planar cuprate superconductors. The data analyzed here suggest an energy scale of 1-10 meV for the breaking of the U(1)-symmetry.

cond-mat.supr-con↗
arXiv2000

Low-energy electron-electron bound states in planar QED

In this talk, we present a parity-preserving QED3 model with spontaneous breaking of a local U(1)-symmetry. The breaking is accomplished by a potential of the phi^6-type. It is shown that a net attractive interaction appears in the Moeller scattering (s- and p-wave scatterings between two electrons) as mediated by the gauge field and a Higgs scalar. We show, by solving numerically the Schroedinger equation for both the scattering potentials (s- and p-wave), that in the weak-coupling regime only s-wave bound states appear, whereas in the strong-coupling regime s- and p-wave bound states show up. Also, we discuss possible applications of the model to the phenomenology of high-Tc superconductors and to the re-entrant superconductivity effect.

hep-th↗
arXiv2000

Gluon distributions in nucleons and pions at a low resolution scale

In this paper we study the gluon distribution functions in nucleons and pions at a low resolution $Q^2$ scale. This is an important issue since parton densities at low $Q^2$ have always been taken as an external input which is adjusted through DGLAP evolution to fit the experimental data at higher scales. Here, in the framework of a model recently developed, it is shown that the hypothetical cloud of {\it neutral} pions surrounding nucleons and pions appears to be responsible for the characteristic valence-like gluon distributions needed at the inital low scale. As an additional result, we get the remarkable prediction that neutral and charged pions have different intrinsic sea flavor contents.

hep-ph↗
arXiv2000

On the thermodynamics of the 2+1 dimensional Gross-Neveu model with complex chemical potential

We study the thermodynamics of the 2+1 dimensional Gross-Neveu model in the presence of a chemical potential by introducing a representation for the canonical partition function which encodes both real and imaginary chemical potential cases. It is pointed out that the latter case probes the thermodynamics of the possible anyon-like excitations in the spectrum. It is also intimately connected to the breaking of the discrete Z-symmetry of a U(1) gauge theory coupled to the Gross-Neveu model at finite temperature, which we interpret as signaling anyon deconfinement. Finally, the chiral properties of the model in the presence of an imaginary chemical potential are discussed and analytical results for the free-energy density at the transition points are presented.

hep-th↗
arXiv1999

Non-BPS Dyons and Branes in the Dirac-Born-Infeld Theory

Non-BPS dyon solutions to D3-brane actions are constructed when one or more scalar fields describing transverse fluctuations of the brane, are considered. The picture emerging from such non-BPS configurations is analysed, in particular the response of the D-brane-string system to small perturbations.

hep-th↗
arXiv1999

The $bar{d} - \bar{u}$ asymmetry of the proton in a Pion Cloud Model approach

We study the $bar{d} - \bar{u}$ asymmetry of the proton in a model approach in which hadronic fluctuations of the nucleon are generated through gluon splitting and recombination mechanisms. Within this framework, it is shown that the \ud asymmetry of the proton is consistently described by including only nucleon fluctuations to $|πN>$ and $|πΔ>$ bound states. Predictions of the model closely agree with the recent experimental data of the E866/NuSea Collaboration.

hep-ph↗
arXiv1999

Instanton effects and chiral symmetry breaking in QCD2

We discuss the spontaneous breakdown of chiral symmetry in Quantum Chromodynamics by considering gluonic instanton configurations in the partition function. It is shown that in order to obtain nontrivial fermionic correlators in a two dimensional gauge theory for the strong interactions among quarks, a regular instanton background has to be taken into account. We work over massless quarks in the -fundamental- representation of SU(N_c). For large N_c, massive quarks are also considered.

hep-th↗
arXiv1998

Strange / anti-strange asymmetry in the nucleon sea

We analyze the non-perturbative structure of the strange sea of the nucleon within a meson cloud picture. In a low $Q^2$ approach in which the nucleon is viewed as a three valon bound state, we evaluate the probability distribution of an in-nucleon Kaon-Hyperon pair in terms of splitting functions and recombination. The resulting kaon and hyperon probability densities are convoluted with suitable strange distributions inside the meson and baryon in order to obtain non-perturbative contributions to the strange sea of the nucleon. We find a structured strange/anti-strange asymmetry, displaying a clear excess of quarks (anti-quarks) for large (small) momentum fractions

hep-ph↗
arXiv1998

Uniqueness of Bogomol'nyi equations and Born-Infeld like supersymmetric theories

We discuss Bogomol'nyi equations for general gauge theories (depending on the two Maxwell invariants $F^{μν} F_{μν}$ and $\tilde F^{μν} F_{μν}$) coupled to Higgs scalars. By analysing their supersymmetric extension, we explicitly show why the resulting BPS structure is insensitive to the particular form of the gauge Lagrangian: Maxwell, Born-Infeld or more complicated non-polynomial Lagrangians all satisfy the same Bogomol'nyi equations and bounds which are dictated by the underlying supersymmetry algebra.

hep-th↗
arXiv1998

N=2-Maxwell-Chern-Simons model with anomalous magnetic moment coupling via dimensional reduction

An N=1--supersymmetric version of the Cremmer-Scherk-Kalb-Ramond model with non-minimal coupling to matter is built up both in terms of superfields and in a component-field formalism. By adopting a dimensional reduction procedure, the N=2--D=3 counterpart of the model comes out, with two main features: a genuine (diagonal) Chern-Simons term and an anomalous magnetic moment coupling between matter and the gauge potential.

hep-th↗
arXiv1997

Bogomol'nyi equations in gauge theories

By imposing self-duality conditions, we obtain the explicit form in which gauge theories spontaneously breakdown in the Bogomol'nyi limit. In this context, we reconsider the Abelian Higgs, Chern-Simons Higgs and Maxwell-Chern-Simons Higgs models. On the same footing, we find a topological Higgs potential for a Maxwell-Chern-Simons extended theory presenting both minimal and nonminimal coupling. Finally, we perform a numerical calculation in the asymmetric phase and show the solutions to the self-dual equations of motion of the topological theory. We argue about certain relations among the parameters of the model in order to obtain such vortex configurations.

hep-th↗
arXiv1996

Fermion Condensates of massless $QED_2$ at Finite Density in non-trivial Topological Sectors

Vacuum expectation values of products of local bilinears $\barψψ$ are computed in massless $QED_2$ at finite density. It is shown that chiral condensates exhibit an oscillatory inhomogeneous behaviour depending on the chemical potential. The use of a path-integral approach clarifies the connection of this phenomenon with the topological structure of the theory.

hep-th↗
arXiv1996

Temperature and Density Effects on the Nucleon Mass Splitting

The finite temperature and finite density dependence of the neutron-proton mass difference is analysed in a purely hadronic framework where the $ρ-ω$ mixing is crucial for this isospin symmetry breakdown. The problem is handled within Thermo Field Dynamics. The present results, consistent with partial chiral and charge symmetry restoration, improve the experimental data fit for the energy difference between mirror nuclei.

hep-ph↗