Existence of Fermion Zero Modes and Deconfinement of Spinons in Quantum Antiferromagnetism resulting from Algebraic Spin Liquid

We investigate the quantum antiferromagnetism arising from algebraic spin liquid via spontaneous chiral symmetry breaking. We claim that in the antiferromagnet massive Dirac spinons can appear to make broad continuum spectrum at high energies in inelastic neutron scattering. The mechanism of spinon deconfinement results from the existence of fermion zero modes in single monopole potentials. Neel vectors can make a skyrmion configuration around a magnetic monopole of compact U(1) gauge fields. Remarkably, in the monopole-skyrmion composite potential the Dirac fermion is shown to have a zero mode. The emergence of the fermion zero mode forbids the condensation of monopoles, resulting in deconfinement of Dirac spinons in the quantum antiferromagnet.Comment: K. -S. Kim is much indebted to Dr. A. Tanaka who pointed out a mistake in association with the gradient expansion in Eq. (C3) and Eq. (C4

Theta-terms in nonlinear sigma-models

We trace the origin of theta-terms in non-linear sigma-models as a nonperturbative anomaly of current algebras. The non-linear sigma-models emerge as a low energy limit of fermionic sigma-models. The latter describe Dirac fermions coupled to chiral bosonic fields. We discuss the geometric phases in three hierarchies of fermionic sigma-models in spacetime dimension (d+1) with chiral bosonic fields taking values on d-, d+1-, and d+2-dimensional spheres. The geometric phases in the first two hierarchies are theta-terms. We emphasize a relation between theta-terms and quantum numbers of solitons.Comment: 10 pages, no figures, revtex, typos correcte

Bad choice design can be particularly harmful for less educated individuals

Imagine you receive a phone call from someone who says they represent your bank

The migration of Ukrainians in times of crisis. OSW COMMENTARY Number 187, 2015-10-19

Before the Russian annexation of Crimea and the outbreak of the conflict in eastern Ukraine, the scale of labour outward migration of Ukrainians had been characterised by a slight downward trend. Back in 2014, an increase in the number of Ukrainians who migrated to Russia was observed, although no similar increase was recorded for EU countries (excluding Poland). The year 2015 brought a more rapid surge in the number of Ukrainians migrating to the EU, again mainly to Poland. Due to the lack of current EU-wide data, estimates can be made based only on data compiled by national statistical offices in countries which are the most popular with Ukrainian migrants. In Poland, as of October 2015 Ukrainians held 52,000 valid residence cards. Much greater migration dynamics have been observed in the case of temporary migration – the number of declarations which enable an individual to take up a temporary job in Poland, issued in the first half of 2015, was a staggering 400,000. This means a more than twofold increase – in the whole of 2014 372,000 declarations were issued to Ukrainian citizens. No similar increase has so far been observed in other EU states, including Italy and the Czech Republic, which have always been popular destinations for Ukrainian migration. In late 2014, 233,000 Ukrainian migrants were registered in Italy (in late 2013 the figure was 191,000), whereas in the Czech Republic the number of Ukrainian migrants remains stable – 104,000 in June 2015

The EU-Ukraine Action Plan on Visa Liberalisation: an assessment of Ukraine's readiness. OSW Commentary No. 45, 2011-01-17

The Action Plan on visas adopted during the recent EU-Ukraine summit is a success for Ukraine. It is the first time that Kyiv has succeeded in obtaining a definition of the conditions and criteria whose fulfilment will enable Ukraine to apply for the lifting of EU visas for its citizens. Ukraine's strong point has been its political will; the lifting of this visa regime has been a priority for all Ukrainian governments since 2005. Since Viktor Yanukovych became president, Ukraine has adopted or prepared key legal acts that brought it nearer to European standards in the area of border and migration management. One of Kyiv's strengths is also its relatively well reformed and efficiently managed border service. Moreover, illegal transit migration via Ukraine is decreasing, and fewer Ukrainians are trying to enter or stay in the EU illegally. Also, Kyiv has efficiently implemented the EU-Ukraine readmission agreement. The hardest task for Ukraine will be to meet the EU’s expectations concerning values, the condition of Ukrainian democracy, and the rule of law. Corruption remains the main barrier to Ukraine's development and modernisation; the courts are weak and the judicial system inefficient. The main undertaking of the new migration service that is being formed at the moment will be to create a civil system of registration, monitoring and regulating the stays of foreign nationals. This may prove difficult, as the supervisory authority (the Ministry of the Interior) remains an unreformed, police-type bureaucratic institution. Ukraine is lagging behind countries such as Russia, Belarus and Moldova when it comes to the introduction of biometric documents. Another problem is the lack of an electronic information system on foreign nationals, visas and border crossings which would be accessible to all the relevant services and institutions. For these reasons, the complete abolition of visas seems to be a longterm perspective, especially considering that many EU countries, which themselves are faced with the problem of migrants’ integration, are rather sceptical about the further liberalisation of movement of people with their eastern neighbours. In the immediate future, if Ukraine meets some of the requirements set by the EU, it will be able to seek the extension of the visa facilitations that have been in operation since 2008

Migration from Ukraine to Poland. The trend stabilises. OSW Report October 2018

The increased wave of migration from Ukraine to Poland which began in 2014 is slowly beginning to decelerate. This migration is still mainly temporary in nature, and it is difficult to assess to what extent it may become fully residential. Probably over the passage of time, the current circular migration model will stop attracting new people. However, Poland remains the main EU country in which Ukrainians work, because of several competitive advantages: extensive migration networks, a liberal procedure for legalising residence and work (for short periods). In addition, despite the fact that the salaries migrants earn in Poland are small compared to countries in the west of the EU, the low living costs allow for regular and relatively high remittances to Ukraine. Poland’s neighbouring countries have started to open up their labour markets to citizens of Ukraine to a limited degree; for example, the Czech Republic has increased its quotas for labour migrants, and Hungary has introduced an easier procedure for acquiring citizenship. Only in Germany do Ukrainians remain marginal among groups of foreign workers. No further rapid increase in migration from Ukraine is possible, due to the country’s dramatic demographic situation, the problems on local labour markets in western Ukraine, and the falling numbers of people of working age

High-energy bremsstrahlung and pair production in the Coulomb field : Bethe and Maximon versus Cheng and Wu approaches

High-energy bremsstrahlung and pair production in the Coulomb field are investigated. The Cheng and Wu impact formula for the amplitude (obtained for a screened potential) is evaluated in the limit when the screening is removed; it is compared then with the high-energy limit of the amplitude calculated by Bethe and Maximon for the unscreened potential. The two limits are shown to be identical provided we calculate correctly the no-screening limit of the Coulomb scattering amplitude. In Cheng and Wu paper this calculation was wrong what led to double counting of the Bethe-Heitler amplitude for pair creation

Urgent problems at small x

Regge theory provides an excellent fit to small-x structure-function data from Q^2=0 right up to the highest available values, but it also teaches us that conventional approaches to perturbative evolution are incorrect.Comment: Talk at DIS99, Zeuthen, April 1999. 3 pages, latex, 3 figure