Regular Series

Vol. 44 (2013), No. 11, pp. 2075 - 2404

XXXVII International Conference of Theoretical Physics Matter to the Deepest

Higgs Boson in the Standard Model and Other Highlights of SM Measurements with the LHC

Acta Phys. Pol. B 44, 2087 (2013)

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In July 2012 the discovery of a new boson with a mass of about 125 GeV and properties in agreement with those expected for the Higgs boson in the Standard Model was announced. In this note, we review the results of the search for the Higgs boson and the study of its properties performed with the proton–proton collision data recorded by the ATLAS and CMS detectors at the LHC in 2011 and 2012, corresponding to an integrated luminosity of 5 fb\(^{-1}\) and 20 fb\(^{-1}\) per experiment at \(\sqrt {s}=7\) TeV and \(\sqrt {s}=8\) TeV, respectively. The presented study confirms the Higgs-like nature of the new boson, with a signal rate consistent with the expectation of the Standard Model, and with the scalar nature of the new boson clearly favoured. In addition, we present studies of the diboson production as an example of a precise electroweak measurement at the LHC. The result, being in agreement with standard model predictions, is interpreted in terms of constraints on anomalous triple-gauge boson couplings.

Searches for Higgs Bosons and Other New Physics in Scenarios Beyond the Standard Model

Acta Phys. Pol. B 44, 2101 (2013)

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Searches are presented for Higgs bosons in scenarios beyond the Standard Model by the ATLAS and CMS experiments at the Large Hadron Collider. Searches for other exotic phenomena are also shown.

The 126 GeV Higgs Boson and Its Natural Relatives

Acta Phys. Pol. B 44, 2113 (2013)

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Assuming that the observed 126 GeV particle at the Large Hadron Collider (LHC) is very close to being the Standard-Model Higgs boson, three examples of extra scalar doublets are discussed where they are set apart from the 126 GeV Higgs boson naturally because of symmetries.

Higgs Boson Decay to \(\gamma Z\) and Test of CP and CPT Symmetries

Acta Phys. Pol. B 44, 2121 (2013)

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Polarization characteristics of \(\gamma Z\) state in the Higgs boson decay \(h \to \gamma Z\) are discussed. Based on the effective Lagrangian, describing \(h \gamma Z\) interaction with CP-even and CP-odd parts, we calculate the polarization parameters \(\xi _1\), \(\xi _2\), \(\xi _3\). A nonzero value of the photon circular polarization, defined by the parameter \(\xi _2\), arises due to the presence of both parts in the effective Lagrangian and its non-Hermiticity. A measurement of the circular polarization through the forward–backward asymmetry of fermions in the decay \(h \to \gamma \, Z \, \to \gamma \, f\, \bar {f}\) will allow one to search for deviation from the Standard Model and a possible violation of the CPT symmetry.

125 GeV Higgs Boson and Radiative Natural SUSY

Acta Phys. Pol. B 44, 2129 (2013)

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The observed mass 125 GeV of the Higgs boson at the LHC requires the large stop mass scale \(M_{\tilde t} \simeq M_{\rm SUSY} \gtrsim 1\) TeV. The allowed region of stop parameters is investigated in MSSM of 3-loop accuracy. There is a sum rule between the MSSM Higgs \(\gamma \gamma \)-, \(b\bar b\)-production cross section ratios to the SM Higgs boson. Radiative natural SUSY (RNS), satisfying the weak-scale naturalness in MSSM, predicts the small Higgsio mass less than 500 GeV. Correspondingly, the \(\gamma \gamma (b\bar b)\) cross section ratio is reduced (enhanced) in RNS.

Lepton Number Violation and Scalar Searches at the LHC

Acta Phys. Pol. B 44, 2139 (2013)

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We review the SM extensions with scalar multiplets including doubly-charged components eventually observable as di-leptonic resonances at the LHC. Special emphasis is paid to the limits on LNV implied by doubly-charged scalar searches at the LHC, and to the characterization of the multiplet doubly-charged scalars belong to if they are observed to decay into same-sign charged lepton pairs.

Searching for Sgluons in the Same-sign Leptons Final State at the LHC

Acta Phys. Pol. B 44, 2149 (2013)

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A simulation of pair production of color-octet scalars (sgluons) decaying into \(t\bar {t}\) is presented. Such particles appear in many extensions of the SM, e.g. in the \(R\)-symmetric SUSY. We search for same-sign dileptons and \(b\)-jets signature of sgluons, focusing on events with a large number of “fat” jets and using the sum of jet masses as a selection criterion. The UNLOPS method, as implemented in PYTHIA8, is used to simulate the SM background.

On Extended GMSB Models

Acta Phys. Pol. B 44, 2155 (2013)

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We discuss some features of unification models in which supersymmetry breaking is transmitted to the visible sector not only via gauge interactions but also by the Yukawa-type couplings of messengers. Examples of low-energy phenomenology of such models are presented.

Higgs \(\to \gamma \gamma \), \(Z\gamma \) in the Inert Doublet Model

Acta Phys. Pol. B 44, 2163 (2013)

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An analysis of the Higgs boson decay rates to \(\gamma \gamma \) and \(Z\gamma \) in the Inert Doublet Model is presented. We study the correlation between the two rates and perform extended analysis of the two-photon rate (\(R_{\gamma \gamma }\)). We study both the possibility of enhancing and suppressing \(R_{\gamma \gamma }\), and find constraints for masses of the scalar particles (in particular the dark matter (DM) candidate and the charged scalar) and their couplings to the Higgs boson. We also combine the resulting constraints with those following from the WMAP measurements of the DM relic density, obtaining stringent constraints on different dark matter scenarios.

Drell–Yan Processes with WINHAC

Acta Phys. Pol. B 44, 2171 (2013)

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We present the Monte Carlo event generator WINHAC for Drell–Yan processes in proton–proton, proton–antiproton, proton–ion and ion–ion collisions. It features multiphoton radiation within the Yennie–Frautschi–Suura exclusive exponentiation scheme with \({\cal O}(\alpha )\) electroweak corrections for the charged-current (\(W^+/W^-\)) processes and multiphoton radiation generated by PHOTOS for neutral-current (\(Z+\gamma \)) ones. For the initial-state QCD/QED parton shower and hadronisation, it is interfaced with PYTHIA. It includes several options, e.g. for the polarized \(W\)-boson production, generation of weighted/unweighted events, etc. WINHAC was cross-checked numerically at the per-mille level with independent Monte Carlo programs, such as HORACE and SANC. It has been used as a basic tool for developing and testing some new methods of precise measurements of the Standard Model parameters at the LHC, in particular the \(W\)-boson mass. Recently, it has been applied to simulations of the double Drell–Yan processes resulting from double-parton scattering, in order to assess their influence on the Higgs-boson detection at the LHC in its \(ZZ\) and \(W^+W^-\) decay channels.

NLO Corrections in the Initial-state Parton Shower Monte Carlo

Acta Phys. Pol. B 44, 2179 (2013)

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The decade-old technique of combining the NLO-corrected hard process with LO-level parton shower Monte Carlo is now mature and used in practice of the QCD calculations in the LHC data analysis. The next step, its extension to an NNLO-corrected hard process combined with the NLO-level parton shower Monte Carlo, will require development of the latter component. It does not exist yet in a complete form. In this note, we describe recent progress in developing the NLO parton shower for the initial-state hadron beams. The technique of adding NLO corrections in the fully exclusive form (defined in recent years) is now simplified and tested numerically, albeit for a limited set of NLO diagrams in the evolution kernels.

The Top–Higgs Coupling at the LHC

Acta Phys. Pol. B 44, 2189 (2013)

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The factorization scale dependence of the anomalous top–Higgs coupling effects in the leading order differential cross sections and distributions of the secondary lepton in the process of associated production of the top-quark pair and the Higgs boson at the LHC is discussed. It is also shown that the differential cross section as a function of the rapidity of the secondary lepton in the process is practically insensitive to a sign of the anomalous pseudoscalar coupling.

Virtual Corrections to the NLO Splitting Functions for Monte Carlo: the Non-singlet Case

Acta Phys. Pol. B 44, 2197 (2013)

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Construction of a QCD cascade at the NLO level requires recalculation of the splitting functions in a different manner. We describe the calculation of some of the virtual contributions to the non-singlet splitting function. In order to be compatible with the earlier calculated real contributions, the principal value prescription for regularizing the infrared singularities must be used in a new way. We illustrate this new scheme on simple examples. For the calculations, we wrote a Mathematica package called Axiloop. We describe its current status.

full authors' list

I. Bierenbaum, P. Draggiotis, S. Buchta, G. Chachamis, I. Malamos, G. Rodrigo

News on the Loop-tree Duality

Acta Phys. Pol. B 44, 2207 (2013)

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We summarize recent developments of the loop-tree duality method at one-loop and higher orders.

Integrand-level Reduction at One and Higher Loops

Acta Phys. Pol. B 44, 2215 (2013)

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The integrand-level reduction of scattering amplitudes is a method for the decomposition of loop integrals which has already been successfully applied and automated at one-loop, and recently extended to higher loops. We present recent developments on the topic, within a coherent framework which can be applied to any integrand at any loop order. We focus on semi-analytic and algebraic techniques, such as the improved one-loop reduction via Laurent series expansion with the library Ninja, and the multi-loop divide-and-conquer approach which can always be used to algebraically find the integrand decomposition of any Feynman graph.

Associated Higgs Production at NLO with GoSam

Acta Phys. Pol. B 44, 2223 (2013)

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Integrand reduction has shown to be an invaluable method for the reduction of scattering amplitudes at one-loop and beyond. The algorithm implemented in Samurai, a Fortran library for \(d\)-dimensional integrand reduction, is discussed, mainly focusing on its novel extension Xsamurai to perform the reduction of higher-rank integrals. GoSam has been used to compute processes of associated Higgs production in Gluon Fusion, Vector Boson Fusion and in combination with a \(t\bar {t}\) pair. In particular, the calculation of Higgs boson plus up to three jets production in the heavy-top effective theory is discussed, where higher-rank integrals may appear.

FormCalc 8: Better Algebra and Vectorization

Acta Phys. Pol. B 44, 2231 (2013)

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We present Version 8 of the Feynman-diagram calculator FormCalc. New features include, in particular, significantly improved algebraic simplification as well as vectorization of the generated code. The Cuba Library, used in FormCalc, features checkpointing to disk for all integration algorithms.

Reductions and Contractions of 1-loop Tensor Feynman Integrals

Acta Phys. Pol. B 44, 2241 (2013)

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We report on the progress in constructing contracted one-loop tensors. Analytic results for rank \(R=4\) tensors, cross-checked numerically, are presented for the first time.

Some Remarks on Non-planar Feynman Diagrams

Acta Phys. Pol. B 44, 2249 (2013)

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Two criteria for planarity of a Feynman diagram upon its propagators (momentum flows) are presented. Instructive Mathematica programs that solve the problem and examples are provided. A simple geometric argument is used to show that while one can planarize non-planar graphs by embedding them on higher-genus surfaces (in the example it is a torus), there is still a problem with defining appropriate dual variables since the corresponding faces of the graph are absorbed by torus generators.

Application of Chiral Resonance Lagrangian Theories to the Muon \(g-2\)

Acta Phys. Pol. B 44, 2257 (2013)

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We think that phenomenological resonance Lagrangian models, constrained by global fits from the low energy hadron reaction data, can help to improve muon \(g-2\) predictions. The main issue are those contributions which cannot be calculated by perturbative means: the hadronic vacuum polarization (HVP) effects and the hadronic light-by-light (HLbL) scattering contribution. I review the recent progress in the evaluation of the HVP contribution within the broken Hidden Local Symmetry (HLS) framework, worked out in collaboration with Benayoun, David and DelBuono. Our HLS driven estimate reads \(a_\mu ^{\rm LO~had}=(688.60\pm 4.24)\times 10^{-10}\) and we find \(a_\mu ^{\rm the}= (11 659 177.65 \pm 5.76)\times 10^{-10}\).

Progress in Analytical Calculations for the Anomalous Magnetic Moment of the Muon

Acta Phys. Pol. B 44, 2267 (2013)

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We present results for certain classes of diagrams contributing to the anomalous magnetic moment of the muon at five-loop order. Our method is based on first constructing an approximating function for the vacuum polarization function of the photon at four-loop order which later can be numerically integrated to obtain the anomalous magnetic moment of the muon.

QED Radiative Corrections for \(\gamma \gamma \)-production of Hadrons in \(e^+ e^-\) Scattering

Acta Phys. Pol. B 44, 2275 (2013)

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The theoretical calculation of the leading quantum electrodynamics radiative corrections to the processes of hadron production via the photon–photon interaction in the electron–positron scattering is briefly reviewed.

FSR Corrections to the Process \(e^+e^- \rightarrow \bar {p} p \gamma \)

Acta Phys. Pol. B 44, 2281 (2013)

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Newly developed model of the nucleon form factors is described and the role of the final state emission in the reaction \(e^+e^-\to \bar p p \gamma \) is discussed.

Rare Muon Decays

Acta Phys. Pol. B 44, 2289 (2013)

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In this paper, we present a short review of searches for charged lepton flavour violation on the example of rare muon decays. We discuss the evaluation of electron spectrum for muon decay in orbit which is a background process for conversion experiments.

Recent Measurements of \(\theta _{13}\) Mixing Angle in Neutrino Oscillation Experiments

Acta Phys. Pol. B 44, 2295 (2013)

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This article presents recent developments in neutrino experimental physics associated with \(\theta _{13}\) oscillation mixing angle measurements. Latest results from reactor (Daya Bay, Reno, Double Chooz) and long baseline (T2K, MINOS) experiments are presented.

Search for Sterile Neutrinos Including Recent Results from the ICARUS Detector in the CNGS Neutrino Beam

Acta Phys. Pol. B 44, 2303 (2013)

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The ICARUS T600 detector at the LNGS Gran Sasso underground Laboratory is the first large mass Liquid Argon Time Projection Chamber (LAr-TPC) designed to study the oscillations of neutrinos from the CERN–CNGS beam, the atmospheric neutrinos and matter stability. In stable conditions, the detector has been collecting data since October 2010 to December 2012. The results, presented here, relate to the search for \(\nu _\mu \to \nu _e\) signal due to the LSND anomaly. The LSND anomaly would manifest itself as an excess of \(\nu _e\) events in \(\nu _{\mu }\) beam. The present analysis is based on a total sample of 1995 events of CNGS neutrino interactions corresponding to \(6\times 10^{19}\) pot. Four clear \(\nu _e\) events have been identified, compared with an expectation of \(6.4 \pm 0.9\) events from conventional sources. The result is compatible with the absence of a LSND anomaly. At 90% and 99% confidence levels, the limits of 3.7 and 8.3 events correspond to oscillation probabilities \(3.4 \times 10^{-3}\) and \(7.6 \times 10^{-3}\), respectively. The result strongly limits the LSND anomaly to a narrow region around \((\Delta m^2,~\sin ^2(2\theta _{\rm new})) = (0.5~{\rm eV}^2,~0.005)\), where there is an overall agreement (90% C.L.) among the present ICARUS limit, the published limits of KARMEN, and the published positive signals of LSND and MiniBooNE collaborations.

Searches for Neutrinoless Double Beta Decay — Results from Phase I of the GERDA Experiment

Acta Phys. Pol. B 44, 2311 (2013)

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The result from Phase I of the Gerda experiment is reported. Gerda is carried out at the Gran Sasso Laboratory of INFN in Italy and searches for neutrinoless double beta decay of \(^{76}\)Ge. According to the performed analysis, the background index after pulse shape discrimination is about \(1\times 10^{-2}\) cts/(keV\(\times \)kg\(\times \)yr). No signal was observed and the derived lower limit for the half-life of neutrinoless double beta decay of \(^{76}\)Ge is T\(^{0\nu }_{1/2} \gt 2.1\times 10^{25}\) yr (90% C.L.). The combination with the results from the former Heidelberg–Moscow and Igex experiments gives an improved limit of T\(^{0\nu }_{1/2} \gt 3.0\times 10^{25}\) yr (90% C.L.).

Up-to-date Results from the Pierre Auger Observatory

Acta Phys. Pol. B 44, 2317 (2013)

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The Pierre Auger Observatory is a state-of-the-art cosmic ray detector, allowing one to analyse the properties of ultra-high energy cosmic rays with unprecedented precision. The observatory, covering an area of 3 000 km\(^2\), combines two different detection techniques, making it the first of its kind. Here, we present some of the most relevant results obtained by this experiment.

Phenomenology of Neutrino Oscillations and Mixing

Acta Phys. Pol. B 44, 2323 (2013)

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We review the status of three-neutrino mixing and the results of global analyses of short-baseline neutrino oscillation data in 3+1 and 3+2 neutrino mixing schemes.

Residual Symmetries in the Lepton Mass Matrices

Acta Phys. Pol. B 44, 2331 (2013)

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It has been suggested that residual symmetries in the charged-lepton and neutrino mass matrices can possibly reveal the flavour symmetry group of the lepton sector. We review the basic ideas of this purely group-theoretical approach and discuss some of its results. Finally, we also list its shortcomings.

Current Status of Constraints on the Elements of the Neutrino Mass Matrix

Acta Phys. Pol. B 44, 2339 (2013)

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We analyse the mass matrix of the three light neutrinos in the basis where the charged-lepton mass matrix is diagonal and discuss constraints on its elements for the Majorana and the Dirac case.

Progress in the Parametrisation of the Neutrino Sector

Acta Phys. Pol. B 44, 2347 (2013)

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Adding gauge singlets to the original Standard Model allows an explanation for the observed smallness of the neutrino masses using the see-saw mechanism. Following our plans presented in the last conference of this series, we present the results for the non-standard setting, when the number of the singlets is smaller than the number of the SM generations.

Attempts at Explaining Neutrino Masses and Mixings Using Finite Horizontal Symmetry Groups

Acta Phys. Pol. B 44, 2353 (2013)

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A brief discussion about the current status of the search for the possible finite symmetry of a leptonic mass matrix is presented. Possible extensions of the models of leptons that can describe the masses and mixing elements are discussed.

Dark Matter Pions

Acta Phys. Pol. B 44, 2359 (2013)

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We study the scenario where dark matter corresponds to a set of pseudo-Goldstone bosons, that we call dark pions, generated by the spontaneous breaking of a symmetry in the dark sector. As a concrete example, we consider an SU\((N) \times {\rm SU}(N)\) broken to the diagonal subgroup that remains an exact symmetry that ensures the stability of the dark pions, and allows a novel-interactions involving neutral gauge bosons and 3 dark pions. We study both experimental and theoretical constraints, and show that the model can accommodate all data in wide regions of parameter space.

Gravitino Dark Matter with Constraints from Higgs Boson Mass and Sneutrino Decays

Acta Phys. Pol. B 44, 2367 (2013)

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We investigate gravitino dark matter produced thermally at high temperatures and in decays of a long-lived sneutrino in the framework of the Non-Universal Higgs Model (NUHM). We apply relevant collider and cosmological bounds. Generally, we find allowed values of the reheating temperature \(T_{\mathrm {R}}\) below \(10^9\) GeV, i.e.  somewhat smaller than the values needed for thermal leptogenesis, even with a conservative lower bound of 122 GeV on the Higgs boson mass. Requiring mass values closer to 126 GeV implies \(T_{\mathrm {R}}\) below \(10^7\) GeV and the gravitino mass less than  \(10\) GeV.

Constraints on Two-component Dark Matter

Acta Phys. Pol. B 44, 2373 (2013)

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We study the ‘Higgs Portal’ 2-component Dark Matter scenario with two interacting cold Dark Matter (DM) candidates: a neutral scalar singlet (\(\varphi \)) and a neutral Majorana fermion (\(\nu \)). The relic abundance of \(\nu \) and \(\varphi \) is found assuming the thermal DM production and solving the Boltzmann equations. We scan over the parameter space of the model to determine regions consistent with the WMAP data for DM relic abundance and the XENON100 direct detection limits for the DM–nucleus cross section.

Modeling Branes in Warped Extra-dimension

Acta Phys. Pol. B 44, 2381 (2013)

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We have presented a generalization of the second Randall–Sundrum model in which different bulk cosmological constants on each side of the brane are allowed. A smooth version of the model was introduced and discussed. We have also considered a scenario with two thick branes which allows to address the issue of the hierarchy problem.

Neutrinos in Proto-neutron Star Models

Acta Phys. Pol. B 44, 2389 (2013)

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The equation of state (EoS) of a hot proto-neutron star matter with trapped neutrinos was calculated within the effective SU\((3)\) theory with the enhanced vector meson sector.

On the Complementarity of Different Cosmological Probes with SLACS, BELLS and SL2S Strong Gravitational Lensing Data

Acta Phys. Pol. B 44, 2397 (2013)

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Accelerating expansion of the Universe is now an indisputable observational fact and became one of the most important issues of both physics and cosmology today, known as dark energy (DE) problem. The nature of this phenomenon is still unknown and from observational point of view the only way to put some light on cosmic expansion history is to combine different methods which are alternative to each other. In this light, we explore the idea that strong gravitational lensing systems offer new opportunity to constrain DE parameters in a way complementary to other cosmological probes. It turns out that the angle of the confidence contour major axis for strong lensing measurements depends on the redshift of the sample what may help to break the degeneracy in the \(w_{0}\)–\(w_{a}\) parameters plane in the Chevalier–Polarski–Linder parametrization of DE equation of state.


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