Strangeness in the nucleon. M.V. Polyakov Bochum University What is known about strangeness in the nucleon ? What is strange in the strange quark matrix elements? Heavy quark limit. Heavy-light duality for strangeness? Exclusive production as effective tool to excite sea

What is known about strangeness in the nucleon ? We learned that strange matrix elements of the typeare nonzero ! Sigma-term and octet mass splitting Polarized DIS Neutrino DIS Strange vector FFs at t=-0.1 GeV^2 from parity violating electron scattering

What is strange in this matrix elements ? That they are non-zero ? That they are large ? That they are small ? Signs?. It is problem only for naive QM Comparing to what ? Comparing to what? How picture of the nucleon would change if I change signs? Let us consider the same matrix elements but for heavy quark Hierarchy! From ~1 to ~1/1000 How to explain? In QCD all matrix elements are of order unity.

[Simulation by D. Leinweber] Topological charge density fluctuations in QCD vacuum (cooled lattice)

Heavy quark mass limit of matrix elements Nucleon‘s slice

Heavy quark mass limit of matrix elements Clear hierarchy of matrix elements ! Schäfer, Teryaev, MVP `99 Franz, Goeke, MVP `00

Hierarchy as for heavy quarks ?

Moreover, substituting mass of strange quark to heavy mass expansion formulae we obtain: It looks like semiclassics is justified by other parameter as heavy quark mass !

If to follow this conjucture we should expect: Why strange quarks in the nucleon behave semiclassically? Or in other words: it looks like the strange quarks „feel“ only gluon operators with low dimensions. To check such conjucture a knowledge of other strange matrix elements is needed!

It seems that all sea distributions of the same order. Some of strange matrix elements in various models Tables from Diehl, Feldmann, Kroll `08

It looks like the strange quarks „feel“ only gluon operators with low dimensions. Interesting problem: perform calcultions of higher order expansion and require the these corrections are small. In this way you obtain relations between nucleon matrix elements of high dim. gluon operators ! One of practical application sof the conjectured hierarchy: shape of C-odd strange parton distribution Possible origin of the hierarchy is the „chiral“ origin of the nucleon sea – natural in the baryon as soliton picture.

Hierarchy conjecture Implies that has several zeros See e.g. Diehl, Feldmann, Kroll `08

CTEQ analysis of parton distributions „Hierarchy conjecture“ can help to constrain the shapes

Diehl, Feldmann, Kroll `08 Strange form factor is too large as compared to our „hierarchy conjecture“. One can tune shape of strange quark distribution to get ~1/10000 for strange FF.

Possible origin of the hierarchy is the „chiral“ origin of the nucleon sea – natural in the baryon as soliton picture. Idea: in the picture of baryons as solitons quarks move in chiral mean-field which we can find requiring the strange vector FFs are anomalously small. In this way one finds chiral Lagrangian!

It is also interesting to see how strange quark behaves in other baryons. For example, in hyperons ! For that hard exclusive production of strangeness is very useful!

Production of anti-strangeness – a way to „turn“ sea quarks into valence

We can design probes by our wish ! See e.g. Goloskokov, Kroll `08 Interesting interference phenomena ! Fun to catch on a collider ! Eides, Frankfurt, Strikman `98

It is also interesting to see how strange quark behaves in other baryons. For example, in hyperons !

Nondiagonal DVCS

a b

Restorable part of GPD is contained in M.V.P. ´07 A. Moiseeva+MVP ´08 Vanderhaeghen+MVP´08

Illustration for Abel tomography How to restore 3D spherically symmetric object from its 2D „fotograph“ Abel, 1826

Additional variables charachterizing meson +N See classification of N->meson +N GPDs In /Stratmann, MVP ´06/

For tomography of DVCS amplitude and GPD quintessence function see Polyakov, PLB659 (2008) 542 QCD string operator

Advantage of QCD strings to excite exotic baryons Strong colour field Strong reararngenemt of colour Hard photon removes a quark from N at once The quark returns back New Narrow Nucleon N*(1685) Revealed in eta photoproduction /Kuznetsov, MVP, JETP Lett. 88 (2008) 399/ This is just one of examples of advantage of QCD string probe for studies of baryon excitations.