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Nils A. Tornqvist

Publications and source records attributed to Nils A. Tornqvist.

At least 19 recordsLinked to original sources
arXiv2011

Heavy Baryons and Exotics Spectrum

We discuss several highly accurate theoretical predictions for masses of baryons containing the b quark which have been recently confirmed by experimental data. Several predictions are given for additional properties of heavy baryons. We also discuss the two charged exotic resonances Z_b with quantum numbers of a (b bbar u ddbar) tetraquark, very recently reported by Belle in the channel [Upsilon(nS) π^+, n=1,2,3]. Among possible implications are deeply bound I=0 counterparts of the Z_b-s and existence of a Sigma_b^+ Sigma_b^- dibaryon, a "beauteron".

hep-ph↗
arXiv2006

The Scalar Mesons, Symmetry Breaking, Three Colors and Confinement

The same, well known, det(Sigma)+ h.c. term in effective theories, which 't Hooft showed is generated by instantons in QCD and which resolves the UA(1) problem giving mass, in particular to the $η'$ is for three light flavors shown to give three classical minima along the UA(1) circle. The three minima are related to the Z(3) center of SU(3). The term also contributes, in a similar way as the diquark model of Jaffe, to an inverted scalar mass spectrum for the light scalars. The three vacua suggests a connection to the strong CP problem and confinement.

hep-ph↗
arXiv2005

Mixing the Strong and E-W Higgs Sectors

After noting the well known similarity of the minimal electro-weak Higgs sector with the linear sigma model for the pion and the sigma, it is found that a small mixing term between the two models generates a pion mass. Although the custodial SU(2)L x SU(2)R, and the gauged SU(2)L x U(1) symmetry for the whole model remains intact, the mixing breaks the relative chiral symmetry between the two sectors. The mixing should be calculable from light quark masses as a quantum correction. This simple mechanism of "relative symmetry breaking" is believed to have applications for other forms of symmetry breaking.

hep-ph↗
arXiv2004

Isospin breaking of the narrow charmonium state of Belle at 3872 MeV as a deuson

The narrow charmonium state near 3872 MeV reported by the Belle collaboration and confirmedby CDF lies almost exactly at the neutral D anti-D* threshold. As was predicted many years ago it can be a deuteronlike meson-meson state called a deuson. If so, it should be an axial, or possibily a pseudoscalar state with C=0, and isospin predominantly 0. Large isospin breaking is expected because of the isospin mass splitting between the neutral and charged D (D*) mesons. Because of this large isospin breaking the decay X(3872) to J/psi rho would be allowed, while J/psi sigma would be forbidden by C-parity, as indicated by the present data.

hep-ph↗
arXiv2004

Comment on the narrow charmonium state of Belle at 3871.8 MeV as a deuson

It is pointed out that the narrow charmonium state at 3871.8 MeV reported by the Belle collaboration is likely to be a $D\bar D^*$ deuteronlike meson-meson state called a deuson. It was predicted near the $D\bar D^*$ threshold over 10 years ago. Its spin-parity would be 0-+ or 1++ and an important decay mode should be via $D^0\bar D^{*0}$ to $D^0\bar D^0π^0$. Its width to that channel should then be of the order 50 keV. Note: A more detailed update of this unpublished note is in hep-ph/0402237.

hep-ph↗
arXiv2002

Scalar mesons above and below 1 GeV

We show that two nonets and a glueball provide a consistent description of data on scalar mesons below 1.7 GeV. Above 1 GeV the states form a conventional (q bar q) nonet mixed with the glueball of lattice QCD. Below 1 GeV the states also form a nonet, as implied by the attractive forces of QCD, but of more complicated nature. Near the center they are 4 quark states of the Jaffe type in S-wave, with some (q bar q) in P-wave, but further out they rearrange in colour to two colourless (q bar q) pairs and finally as meson-meson states. A simple effective chiral model for such a system with two scalar nonets can be made involving two coupled linear sigma models. One of these could be looked upon as the Higgs sector of nonpertubative QCD.

hep-ph↗
arXiv2002

The lightest scalar nonet

First I review some previous work on the lightest scalars below 1.5 GeV, and how these scalars can be understood as unitarized nonet states. The bare scalars are strongly distorted by hadronic mass shifts, and the lightest I=0 state becomes a very broad resonance of mass and width of about 500 MeV. This is the sigma meson required by models based on linear realization of chiral symmetry. Recently the light sigma has clearly been observed in D decay to 3 pions by the E791 experiment at Fermilab and I discuss how this decay channel can be predicted in a Constituent Quark Meson Model, which incorporates heavy quark and chiral symmetries. At the end I discuss the likely possibility that there are in fact two light scalar nonets, such as one mainly meson-meson (or 4-quark) nonet and one qq bar nonet. I point out that an interesting approximate description of this could be modelled by starting with two coupled linear sigma models. After gauging the overall symmetry one of these could be looked upon as the "Higgs sector of strong interactions", and the lightest scalar nonet becomes the corresponding Higgs nonet.

hep-ph↗
arXiv2002

The Lightest Scalar Nonet as Higgs Bosons of Strong Interactions

I discuss how an extra light scalar meson multiplet could be understood as an effective Higgs nonet of a hidden local U(3) symmetry. There is growing evidence that low energy data requires in addition to a conventional (q bar q) nonet near 1.4 GeV, another light scalar nonet-like structure below 1 GeV, (sigma(600), a_0(980), f_0(980), kappa), which could be interpreted as such a Higgs nonet.

hep-ph↗
arXiv2000

Summary talk at the conference on the sigma resonance

This report summarizes the most important results presented at the recent conference held at the Yukawa Institute of Theoretical Physics in Kyoto, devoted to the recently confirmed light sigma resonance. Remarkably, all speakers at this meeting took the light sigma for granted and many mass and width estimations near 500 MeV were presented. We emphasize that if the light and broad sigma is accepted as a true resonance it explains many basic problems of low energy hadronic physics in a simple way, especially if the linear sigma model is used as an approximate effective low energy theory.

hep-ph↗
arXiv2000

How to understand the lightest scalars

Based on previous papers I discuss how I understand the lightest scalars using a general coupled channel model. This model includes all light two-pseudoscalar thresholds, constraints from Adler zeroes, flavour symmetric couplings, unitarity and physically acceptable analyticity. One finds that with a large coupling there can appear two physical resonance poles on the second sheet although only one bare quark-antiquark state is put in. The f0(980) and f0(1370) resonance poles are thus in this model two manifestations of the same strange-antistrange quark state. On the other hand, the isoscalar state containing u and d quarks becomes (when unitarized and strongly distorted by hadronic mass shifts) a very broad resonance, with its pole at 470-i250 MeV. This is the sigma meson required by models for spontaneous breaking of chiral symmetry.

hep-ph↗
arXiv1999

The light scalars and the broad sigma(500) in the U3xU3 linear sigma model

The lightest scalar and pseudoscalar nonets are discussed within the [A framework of the broken old UxU3 linear sigma model, and it is shown that already at the tree level this model works remarkably well predicting scalar masses and couplings not far from present experimental values, when all parameters are fixed from the pseudoscalar masses and decay constants. The linear sigma model is the simplest way to implement chiral symmetry together with the broken SU3 of the quark model, and this, not well known, success in understanding experiment is comparable to that of the naive quark model for the heavier multiplets. It is argued that this strongly suggest that the light and very broad sigma resonance exists near 500 MeV.

hep-ph↗
arXiv1999

Flavour symmetry as a Spontaneously Broken Discrete Permutation Symmetry Embedded in Colour

A new mechanism for breaking an internal symmetry spontaneously is discussed, which is intermediate between the Nambu-Goldstone and Wigner modes of symmetry breaking. Here the quark-antiquark sea takes the role of the vacuum of the Nambu-Goldstone case. Flavour symmetry becomes a discrete permutation symmetry of the valence quarks with respect to the sea quarks, which can be spontaneously broken without generation of massless Goldstone bosons.

hep-ph↗
arXiv1999

Comparing the Broken U3xU3 Linear Sigma Model with Experiment. U3xU3

The linear sigma model with broken U3xU3 is compared with data on the lightest scalar and pseudoscalar mesons. When 5 of the 6 parameters are fixed by the pseudoscalar masses and decay constants one finds that, already at the tree level, a reasonable description for the 4 scalar masses, mixing and up to 8 tri-linear couplings of lightest scalars, taken as a0(980), f0(980), sigma(500) and K*0(1430). This clearly indicates that these scalars are the chiral partners of the pi, eta, eta', K and strongly suggests that they like the latter are (unitarized) quark-antiquark states.

hep-ph↗
arXiv1999

Does the light and broad sigma(500) exist?

The lightest scalar and pseudoscalar nonets are discussed within the framework of the broken U3$\times$U3 linear sigma model, and it is shown that already at the tree level this model works remarkably well predicting scalar masses and couplings not far from present experimental values, when all parameters are fixed from the pseudoscalar masses and decay constants. It is argued that this strongly suggests that the light and very broad $σ$ resonance exists near 500 MeV.

hep-ph↗
arXiv1998

Spontaneous Generation of Pseudoscalar Mass in the U(3)xU(3) Linear Sigma Model

A novel, nonperturbative, way to generate chiral symmetry breaking within the linear sigma model for 3 flavours is discussed. After spontaneous chiral symmetry breaking in the vacuum at the tree level the scalar nonet obtains mass, while the pseudoscalars are massless. Then, including quantum loops in a nonperturbative, self-consistent way chiral symmetry is broken by nonplanar graphs in a second step, and also the pseudoscalars become massive. By interpreting the basic symmetry to be a discrete permutation symmetry, in accord with superselection rules, no additional Goldstone bosons are expected.

hep-ph↗
arXiv1997

Breaking SU3f Spontaneously Down to Isospin

The mechanism where flavour symmetry is broken spontaneously is demonstated for a model involving nonets of pseudoscalar and vector mesons. Degenerate bare nonets of vector and pseudoscalar mesons coupling sufficiently strongly to each others lead to unstable self-consistency equations, such that the SU3$_f$ symmetric spectrum breaks down into a stable isospin symmetric mass spectrum similar to the physical spectrum.

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