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Introduction Symmetry breaking and tetraquarks The additive model of tetraquark confinement The Steiner-tree model of confinement Conclusions Tetraquarks in the Steiner tree model of confinement available at http://lpsc.in2p3.fr/theorie/Richard/SemConf/Talks.html Jean-Marc Richard Laboratoire de Physique Subatomique et Cosmologie Universit´ e Joseph Fourier–IN2P3-CNRS–INPG Grenoble, France Fifth Critical Stability Workshop, Erice, 2008 JMR Steiner tree

Introduction Symmetry breaking and tetraquarks The additive model of tetraquark confinement The Steiner-tree model of confinement Conclusions Table of contents 1 Introduction Symmetry breaking and tetraquarks 2 3 The additive model of tetraquark confinement 4 The Steiner-tree model of confinement 5 Conclusions JMR Steiner tree

Introduction Symmetry breaking and tetraquarks The additive model of tetraquark confinement The Steiner-tree model of confinement Conclusions Introduction Speculations on multiquarks low mass of ( q ¯ q ) , hence ( qq ¯ q ¯ q ) in S-wave perhaps lighter than ( q ¯ q ) in P-wave. Applied to the problem of scalar mesons. Peculiar features of chiral dynamics. Speculations on the late pentaquarks made of light or strange quarks or antiquarks, Coherences in the hyperfine interaction → see next section, Properties of the mass dependence in a flavour-independent potential, → below Favourable 4-body interaction in QCD → below. JMR Steiner tree

Introduction Symmetry breaking and tetraquarks The additive model of tetraquark confinement The Steiner-tree model of confinement Conclusions Symmetry breaking and tetraquarks-1 Consider H = H 0 ( even ) + λ H 1 ( odd ) . Then for the ground state, with ψ 0 ( H 0 ) as trial w.f, � ψ 0 | H 1 | ψ 0 � = 0 E ( H ) ≤ E ( H 0 ) , i.e., H benefits of symmetry breaking. For instance E ( p 2 + x 2 + λ x ) = 1 − λ 2 / 4. This is very general. Starting, e.g., from a symmetrical four-body system ( µ, µ, ¯ µ, ¯ µ ) breaking particle identity or charge conjugation lowers the ground state, but has different consequences on stability JMR Steiner tree

Introduction Symmetry breaking and tetraquarks The additive model of tetraquark confinement The Steiner-tree model of confinement Conclusions Breaking particle identity H ( M , m , M , m ) , where V does not change if M and/or m is modified, can be rewritten as � 1 � 1 � � � � 4 M + 1 4 M − 1 � � p 2 1 + · · · + p 2 p 2 1 − p 2 2 + p 2 3 − p 2 H = + V + 4 4 4 m 4 m � �� � � �� � H 0 H 1 Thus E ( H ) ≤ E ( H 0 ) . But in general, the threshold also benefits from this symmetry breaking, and actually benefits more, so that four-body binding deteriorates. For instance, in atomic physics ( e + , e + , e − , e − ) and any equal-mass ( µ + , µ + , µ − , µ − ) weakly bound below the atom–atom threshold, but ( M + , m + , M − , m − ) unstable for M / m � 2 . 2, see Dario. Then: breaking the symmetry of identical particles does not help JMR Steiner tree

Introduction Symmetry breaking and tetraquarks The additive model of tetraquark confinement The Steiner-tree model of confinement Conclusions Breaking charge conjugation H ( M , M , m , m ) written as � 1 � 1 � � � � 4 M + 1 4 M − 1 � � p 2 1 + · · · + p 2 p 2 1 + p 2 2 − p 2 3 − p 2 H = + V + 4 4 4 m 4 m � �� � � �� � H 0 H 1 still benefits to the four-body system, E ( H ) ≤ E ( H 0 ) , but H and H 0 have the same threshold ( M + , m − ) + ( M + , m − ) . Hence binding improves. Indeed, H 2 more bound than Ps 2 and has even a rich spectrum of excitations. JMR Steiner tree

Introduction Symmetry breaking and tetraquarks The additive model of tetraquark confinement The Steiner-tree model of confinement Conclusions Quark model analogs For a central, flavour-independent, confining interaction V , Equal mass case ( q , q , ¯ q , ¯ q ) hardly bound Hidden-flavour case ( Q , q , Q , ¯ q ) even farther from binding, ( QQ ¯ q ¯ q ) with flavour = 2 bound if M / m large enough See Ader et al. (then at CERN), Heller et al. (Los Alamos), Zouzou et al. (Grenoble), D. Brink et al. (Oxford), Rosina et al. (Slovenia), Lipkin, Vijande et al., etc. ( QQ ¯ q ¯ q ) expected at least in the limit of large or very large M / m . As compared to the “colour-chemistry” (late 70’s and early 80’s) no exotic colour configuration for large M / m , almost pure 3 → ¯ 3 for ( QQ ) as in every baryon, and then ¯ 3 × ¯ 3 × ¯ 3 → 1 for [( QQ ) − ¯ q ¯ q ] as in every antibaryon: well probed colour structure. JMR Steiner tree

Introduction Symmetry breaking and tetraquarks The additive model of tetraquark confinement The Steiner-tree model of confinement Conclusions The additive model of tetraquark confinement Questions: What is V for tetraquarks? Even earlier: what is the link from mesons to baryons? The additive model By analogy with QED, V ( 1 , 2 , . . . ) = − 3 � λ ( c ) λ ( c ) ˜ . ˜ v ( r ij ) , i j 16 i < j v ( r ) is the quarkonium potential fitted to mesons, λ ( c ) is the non-abelian colour operator Consequences A reasonable simultaneous phenomenology of baryon and meson spectra Multiquarks unbound, except ( QQ ¯ q ¯ q ) with large M / m . Hence multiquark binding was based on other mechanisms: chrmomagnetism (Jaffe, Lipjkin, Gignoux et al.), chiral dynamics (cf. the late pentaquark), etc. JMR Steiner tree

Introduction Symmetry breaking and tetraquarks The additive model of tetraquark confinement The Steiner-tree model of confinement Conclusions The Steiner-tree model of baryons Y -shape potential: Proposed by Artru, Dosch, Merkuriev, etc., proposed a better ansatz, often verified and rediscovered (strong coupling, adiabatic bag model (Kuti et al.), flux tube, lattice QCD, etc.) The linear q − ¯ q potential of mesons interpreted as minimising the gluon energy in the flux tube limit The q − q − q potential of baryons is with the junction optimised, i.e., fulfilling the conditions of the well-known Fermat-Torricelli problem. This potential was used for baryons (Taxil et al., Semay et al., Kogut et al.), but it does not make much difference as compared with the additive ansatz. JMR Steiner tree

Introduction Symmetry breaking and tetraquarks The additive model of tetraquark confinement The Steiner-tree model of confinement Conclusions The Steiner tree model of tetraquarks A tempting generalisation to tetraquarks is the combination V 4 = min ( V f , V S ) of flip-flop V f (already used in its quadratic version by Lenz et al.) V f = λ min ( r 13 + r 24 , r 23 + r 14 ) and Steiner-tree V S V S = λ min k ,ℓ ( r 1 k + r 2 k + r k ℓ + r ℓ 3 + r ℓ 4 ) . J. Carlson and V.R. Pandharipande concluded that this potential does not bind, but JMR Steiner tree

Introduction Symmetry breaking and tetraquarks The additive model of tetraquark confinement The Steiner-tree model of confinement Conclusions The Steiner tree model of tetraquarks A tempting generalisation to tetraquarks is the combination V 4 = min ( V f , V S ) of flip-flop V f (already used in its quadratic version by Lenz et al.) V f = λ min ( r 13 + r 24 , r 23 + r 14 ) and Steiner-tree V S V S = λ min k ,ℓ ( r 1 k + r 2 k + r k ℓ + r ℓ 3 + r ℓ 4 ) . J. Carlson and V.R. Pandharipande concluded that this potential does not bind, but they used too simple trial wave functions for the 4-body problem, and did not consider unequal masses. JMR Steiner tree

Introduction Symmetry breaking and tetraquarks The additive model of tetraquark confinement The Steiner-tree model of confinement Conclusions Tetraquarks in the minimal-path model-1 Vijande, Valcarce and R. revisited the calculation of Carlson at al. with a basis of correlated Gaussians (matrix elements painfully calculated numerically), and obtained stability for ( QQ ¯ q ¯ q ) even for M / m = 1, but better stability for M / m ≫ 1. u = ( E th − E 4 ) / E th JMR Steiner tree

Introduction Symmetry breaking and tetraquarks The additive model of tetraquark confinement The Steiner-tree model of confinement Conclusions Tetraquarks in the minimal-path model-2 A More recently, Cafer Ay, Hyam C Rubinstein (Melbourne) and R.: rigorous proof of stability within the J minimal-path model if M ≫ m . I x Obviously, y z V 4 ≤ V S ≤ | x | + | y | + | z | where x = − → y = − → AB , CD , and z links the middles. B D Then � � � p 2 � p 2 � � p 2 y x z H ≤ M + | x | + m + | y | + 2 µ + | z | exactly solvable, but not does not demonstrate binding of ( QQ ¯ q ¯ q ) JMR Steiner tree

Introduction Symmetry breaking and tetraquarks The additive model of tetraquark confinement The Steiner-tree model of confinement Conclusions Better bound A better bound demonstrates stability for large M / m : √ √ � � � � � p 2 � p 2 p 2 3 3 y x z H ≤ M + 2 | x | + m + 2 | y | + 2 µ + | z | p 2 + | x | = ⇒ e 0 = 2 . 3381 ... (Airy function) e 0 λ 2 / 3 m − 1 / 3 . by scaling p 2 / m + λ | x | = ⇒ Threshold 2 ( Q ¯ q ) Q ¯ q ) at E th = 2 e 0 µ − 1 / 3 , µ = Mm / ( M + m ) . The tetraquark energy has a upper bound �� 3 � � 1 / 3 � M − 1 / 3 + m − 1 / 3 � E 4 ≤ E up + ( 2 µ ) − 1 / 3 4 = e 0 4 Straightforward to check that E up 4 < E th for M / m < 6403 Thus E 4 < E th at large M / m demonstrated rigorously Actually ∀ M / m from solving numerically the 4-boby pb. JMR Steiner tree