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Hlinka J.,ASCR Institute of Physics Prague
Physical Review Letters | Year: 2014

The Letter draws the attention to the spatiotemporal symmetry of various vectorlike physical quantities. The symmetry is specified by their invariance under the action of symmetry operations of the nonrelativistic space-time rotation group O(3)×{1,1′}=O′(3), where 1′ is a time-reversal operation, the symbol×stands for the group direct product, and O(3) is a group of proper and improper rotations. It is argued that along with the canonical polar vector, there are another seven symmetrically distinct classes of stationary physical quantities, which can be - and often are - denoted as standard three-component vectors, even though they do not transform as a static polar vector under all operations of O′(3). The octet of symmetrically distinct "directional quantities" can be exemplified by two kinds of polar vectors (electric dipole moment P and magnetic toroidal moment T), two kinds of axial vectors (magnetization M and electric toroidal moment G), two kinds of chiral "bidirectors" C and F (associated with the so-called true and false chirality, respectively) and still another two bidirectors N and L, achiral ones, transforming as the nematic liquid crystal order parameter and as the antiferromagnetic order parameter of the hematite crystal α-Fe2O3, respectively. © 2014 American Physical Society.

Tasevsky M.,ASCR Institute of Physics Prague
European Physical Journal C | Year: 2013

We investigate the prospects for Central Exclusive Production (CEP) of MSSM Higgs bosons at the LHC using forward proton detectors proposed to be installed at 220 m and 420 m distance around ATLAS and / or CMS. We summarize the situation after the first and very successful data taking period of the LHC. The discovery of a Higgs boson and results from searches for additional MSSM Higgs bosons from both the ATLAS and CMS experiments, based on data samples each corresponding to about 25 fb-1, have recently led to a proposal of new low-energy MSSM benchmark scenarios. The CEP signal cross section for the process H/h →b̄b and its backgrounds are estimated in these new scenarios. We also make some comments about the experimental procedure if the proposed forward proton detectors are to be used to measure the CEP signal. © 2013 Springer-Verlag Berlin Heidelberg and Società Italiana di Fisica.

Macchi A.,National Research Council Italy | Macchi A.,University of Pisa | Borghesi M.,Queen's University of Belfast | Borghesi M.,ASCR Institute of Physics Prague | Passoni M.,Polytechnic of Milan
Reviews of Modern Physics | Year: 2013

Ion acceleration driven by superintense laser pulses is attracting an impressive and steadily increasing effort. Motivations can be found in the applicative potential and in the perspective to investigate novel regimes as available laser intensities will be increasing. Experiments have demonstrated, over a wide range of laser and target parameters, the generation of multi-MeV proton and ion beams with unique properties such as ultrashort duration, high brilliance, and low emittance. An overview is given of the state of the art of ion acceleration by laser pulses as well as an outlook on its future development and perspectives. The main features observed in the experiments, the observed scaling with laser and plasma parameters, and the main models used both to interpret experimental data and to suggest new research directions are described. © 2013 American Physical Society.

Tasevsky M.,ASCR Institute of Physics Prague
International Journal of Modern Physics A | Year: 2014

We review activities in the field of theoretical, phenomenological and experimental studies related to the production of the Higgs boson in central exclusive processes at LHC in models beyond Standard Model. Prospects in the context of the Higgs boson discovery at LHC in 2012 and of proposals to build forward proton detectors at ATLAS and CMS side are summarized. © World Scientific Publishing Company.

Erler T.,ASCR Institute of Physics Prague
Journal of High Energy Physics | Year: 2011

We present a class of analytic solutions of cubic superstring field theory in the universal sector on a non-BPS D-brane. Computation of the action and gauge invariant overlap reveal that the solutions carry half the tension of a non-BPS D-brane. However, the solutions do not satisfy the reality condition. In fact, they display an intriguing topological structure: We find evidence that conjugation of the solutions is equivalent to a gauge transformation that cannot be continuously deformed to the identity. © SISSA 2011.

Erler T.,ASCR Institute of Physics Prague
Journal of High Energy Physics | Year: 2013

We present an analytic solution for tachyon condensation on a non-BPS D-brane in Berkovits' open superstring field theory. The solution is presented as a product of 2 x 2 matrices in two distinct GL2 subgroups of the open string star algebra. All string fields needed for computation of the nonpolynomial action can be derived in closed form, and the action produces the expected non-BPS D-brane tension in accordance with Sen's conjecture. We also comment on how D-brane charges may be encoded in the topology of the tachyon vacuum gauge orbit. © SISSA 2013.

Zavada P.,ASCR Institute of Physics Prague
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

The Cahn effect and the unintegrated unpolarized parton distribution function f1q(x,pT) are studied in a covariant approach. The Cahn effect is compared with some other effects due to the parton intrinsic motion. The comparison suggests that the present understanding of parton transverse momenta and intrinsic motion in general is still rather incomplete. The new relation for f1q(x,pT) is obtained in the framework of the covariant parton model from which a prediction for this distribution function follows. © 2011 American Physical Society.

Zavada P.,ASCR Institute of Physics Prague
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We study the covariant version of the quark-parton model, in which the general rules of the angular momentum composition are accurately taken into account. We demonstrate how these rules affect the relativistic interplay between the quark spins and orbital angular momenta, which collectively contribute to the proton spin. The spin structure functions g1 and g2, corresponding to the many-quark state J=1/2, are studied, and it is shown they satisfy constraints and relations, which fit well the available experimental data including the data on proton spin content ΔΣ. The suggested Lorentz-invariant three-dimensional approach for calculation of the structure functions is compared with the approach based on the conventional collinear parton model. © 2014 American Physical Society.

Paidar V.,ASCR Institute of Physics Prague
Progress in Materials Science | Year: 2011

The changes of sample shape are caused by plastic deformation or by martensitic phase transformations. In both cases the mechanisms of atomic rearrangements are based on collective displacements of atomic aggregates. The internal structure of dislocations, carriers of plastic deformation, can be examined using the energies of generalized stacking faults displayed by so called γ-surfaces calculated for bcc metals by Vasek Vitek already more than 40 years ago. This approach can be extended to the shuffling of atomic planes that plays a crucial role in martensitic phase transformations. Similarities and differences between displacive processes of lattice shearing and atomic plane alternate shuffling are discussed. © 2011 Elsevier Ltd. All rights reserved.

Kunes J.,ASCR Institute of Physics Prague
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We present an efficient and numerically stable algorithm for calculation of two-particle response functions within the dynamical mean-field theory. The technique is based on inferring the high-frequency asymptotic behavior of the irreducible vertex function from the local dynamical susceptibility. The algorithm is tested on several examples. In all cases rapid convergence of the vertex function toward its asymptotic form is observed. © 2011 American Physical Society.

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