arXiv subjects

Dmitri Diakonov

Publications and source records attributed to Dmitri Diakonov.

67 records · Page 4Linked to original sources

arXiv1998

Chiral Quark-Soliton Model

The Chiral Quark-Soliton Model of nucleons is based on two ideas: 1) the major role of spontaneous chiral symmetry breaking in hadron physics and 2) the relevance of the large number of colours limit for the real world. In these lectures I review the theoretical foundations of the model, the physics involved, and some of applications. Contents: 1. How do we know chiral symmetry is spontaneously broken? 2. Low-energy limit of QCD from instantons 2.1. Some of the results 2.2. Instanton-induced interactions 2.3. Bosonization 2.4. Chiral lagrangian 3. Properties of the chiral lagrangian 3.1. Derivative expansion and interpolation formula 3.2. The Wess-Zumino term and the baryon number 4. The nucleon 4.1. Physical motivations 4.2. Nucleon mass: a functional of the pion field 4.3. Nucleon profile 4.4. Quantum numbers of baryons 4.5. Some applications 4.6. Nucleon structure functions 5. Conclusions

hep-ph↗

arXiv1996

Distribution of Instanton and Monopole Clustering

We study the relation between the instanton distribution and the monopole loop length in the SU(2) gauge theory with the abelian gauge fixing. We measure the monopole current from the multi-instanton ensemble on the $16^4$ lattice using the maximally abelian gauge. When the instanton density is dilute, there appear only small monopole loops. On the other hand, in the dense case, there appears one very long monopole loop, which is responsible for the confinement property, in each gauge configuration. We find a clear monopole clustering in the histogram of the monopole loop length from 240 gauge configurations.

hep-lat↗

arXiv1996

Instanton, Monopole and Confinement

We study the correlation between instantons and QCD-monopoles both in the lattice gauge theory and in the multi-instanton system using the maximally abelian gauge. First, we find the existence of an almost linear correlation between the total length of monopole trajectories and the total number of pseudoparticles (instantons and anti-instantons) in the $16^{3}\times4$ SU(2) lattice. Second, we study the features of QCD-monopole in the SU(2) multi-instanton vacuum on the $16^{4}$ lattice as a random ensemble of pseudoparticles. A signal of monopole condensation is found as the clustering of monopole trajectories, when the topological pseudoparticles is sufficiently dense.

hep-lat↗

arXiv1996

Clustering of Monopoles in the Instanton Vacuum

We generate a random instanton vacuum with various densities and size distributions. We perform numerically the maximally abelian gauge fixing of these configurations in order to find monopole trajectories induced by instantons. We find that instanton-induced monopole loops form enormous clusters occupying the whole physical volume, provided instantons are sufficiently dense. It indicates that confinement might be caused by instantons.

hep-lat↗

arXiv1996

Non-Abelian Stokes Theorem and Quark-Monopole Interaction

We derive a new non-abelian Stokes theorem by rewriting the Wilson loop as a gauge-invariant area integral, at the price of integrating over an auxiliary field from the coset SU(N) / [U(1)]^{N-1} space. We then introduce the relativistic quark--monopole interaction as a Wess--Zumino-type action, and extend it to the non-abelian case. We show that condensation of monopoles and confinement can be investigated in terms of the behaviour of the monopole world lines. One can thus avoid hard problems of how to introduce monopole fields and dual Yang--Mills potentials.

hep-th↗

arXiv1996

Foundations of the Constituent Quark Model

'Constituent quarks' means massive quarks, in contrast to the nearly massless u,d,s quarks of the QCD lagrangian. The dynamical or constituent masses appear owing to the spontaneous chiral symmetry breaking in QCD. A realistic mechanism of the chiral symmetry breaking is provided by instantons. Therefore, I review the present status of the QCD instanton vacuum, emphasizing the mechanism of chiral symmetry breaking and of the generation of the constitutent quark mass. I end up with the Nambu--Jona-Lasinio-type effective theory to which QCD is reduced at low momenta.

nucl-th↗

arXiv1996

Spontaneous annihilation of high-density matter in the electroweak theory

In the presence of fermionic matter the topologically distinct vacua of the standard model are metastable and can decay by tunneling through the sphaleron barrier. This process annihilates one fermion per doublet due to the anomalous non-conservation of baryon and lepton currents and is accompanied by a production of gauge and Higgs bosons. We present a numerical method to obtain local bounce solutions which minimize the Euclidean action in the space of all configurations connecting two adjacent topological sectors. These solutions determine the decay rate and the configuration of the fields after the tunneling. We also follow the real time evolution of this configuration and analyze the spectrum of the created bosons. If the matter density exceeds some critical value, the exponentially suppressed tunneling triggers off an avalanche producing an enormous amount of bosons.

hep-ph↗

arXiv1996

Chiral Symmetry Breaking by Instantons

This is a review of the QCD instanton vacuum. After introducing instantons and their physical meaning, I show that the number of instantons in the vacuum fluctuates in accordance with the QCD trace anomaly. The main properties of the instanton ensemble are given. Chiral symmetry breaking by instantons is explained in three different though mathematically equivalent ways. In particular, a derivation of the Nambu--Jona-Lasinio-type model from instantons is presented, and the effective chiral lagrangian to which QCD is reduced at low momenta, is given. I end up by discussing possible confinement mechanisms.

hep-ph↗

arXiv1996

Decay of high-density matter in the electroweak theory

High-density fermion matter is meta-stable due to the anomalous non-conservation of baryon and lepton numbers in the electroweak theory. The meta-stable state decays by penetrating the sphaleron barrier separating topologically different vacua. The decay happens locally, and results in an annihilation of twelve fermions, accompanied by a production of gauge and Higgs bosons. We find numerically local bounce solutions determining the decay rate, which are classical paths in imaginary time, connecting two adjacent topological sectors. We also follow the real-time evolution of the bosonic fields after the tunneling and analyze the spectrum of the created bosons.

hep-ph↗

arXiv1995

Dynamical Higgs Mechanism without Elementary Scalars: A Lesson from Instantons

The generation of gauge--dependent fermion vacuum condensates in Yang--Mills theory would dynamically break the gauge symmetry and thus provide an alternative to the Higgs mechanism in unified theories. We explore a simple example: instanton-induced quark pair (diquark) condensation in QCD with 2 flavors and $N_c$ colors. We do find diquark condensates in the vacuum, but only for $N_c = 2$, where they are equivalent to the standard quark-antiquark condensate. At $N_c \geq 3$ diquark condensates exist as meta--stable saddle points of the instanton-induced effective QCD action and may strongly affect the properties of matter under extreme conditions. The scalar diquark excitation, which is a Goldstone boson at $N_c =2$, becomes unbound for $N_c \geq 3$.

hep-ph↗

arXiv1994

Loop corrections to the sphaleron transition rate in the minimal standard model

The baryon number dissipation rate due to sphaleron transitions at high temperatures in the minimal standard model is evaluated. We find that this rate can be considerably suppressed by one loop contributions of bosonic and fermionic fluctuations which are particularly important for a small mass of the Higgs boson and a large top quark mass. Fixing the latter to its recently stated value of 174 GeV the complete erasure of the baryon asymmetry is prevented within the framework of the minimal standard model if the Higgs mass is less than about 66 GeV.

hep-ph↗

arXiv1994

Fermion sea along the sphaleron barrier

In this revised version we have improved the treatment of the top and bottom quark mass. This leads to slight changes of the numerical results, especially of those presented in Fig.4. The discussion of the numerical procedure and accuracy has been extended.

hep-ph↗

arXiv1993

On semi-classical pion production in heavy ion collisions

In high energy heavy ion collisions the pion multiplicity is large, and one might expect that pions are radiated semi-classically. The axial symmetry of the collision and approximately zero isotopic spin of the colliding nuclei result then in peculiar isotopic spin -- azimuth correlations of the produced pions. These correlations are easy to test -- and should be tested.

hep-ph↗