abstract

This article gives a short overview of the future high-energy \(e^+e^-\) collider projects. Both, linear and circular colliders offer an excellent potential for precision physics and are shortly discussed.

abstract

High energy, high luminosity, future lepton colliders, circular or linear, may possibly give us a hint about fundamental laws of Nature governing at very short distances and very short time intervals, the same which have brought our Universe to live. Currently considered projects are on the one hand, linear electron–positron colliders, which offer higher energy and lower beam intensities and on the other hand, circular electron–positron colliders, limited in energy but offering tremendous interaction rates. On the far future horizon, muon circular colliders are the only viable projects which can explore \(\gt 10\) TeV teritory of the lepton colliders. Experiments in all these future colliders will require theoretical calculations, mainly of the Standard Model processes (including QED), at the precision level one or even two orders better than available today. After brief characterization of theory puzzles in the fundamental interactions, we shall overview main challenges in the precision calculations of the Standard Model effects, which have to be removed from data in order to reveal traces of new unexpected phenomena.

abstract

Light sterile neutrinos with a mass around 1 eV have been studied for many years as a possible explanation of the so-called short-baseline neutrino oscillation anomalies. Recently, several neutrino oscillation experiments reported preferences for non-zero values of the mixing angles and squared mass differences for active–sterile mixing which are, however, not always in agreement. I review our current knowledge on the light sterile neutrino in the 3+1 model, starting with a separate discussion on the status of the most relevant searches and then analyzing the problems that arise when combining different probes in a global fit. A short summary on the tension with cosmological observations is also provided.

abstract

Singular values provide a method to study mixing matrices in particle physics. The methods of unitary dilations and the cosine–sine matrix decomposition are discussed in the framework of the Standard Model neutrinos mixing with one non-standard neutrino. We show that the mixings are continuous functions of singular values. It implies that the magnitude of non-standard mixing can be estimated from below and above unambiguously from the experimentally determined interval PMNS mixing matrix.

abstract

We present a comparison of pole mass calculations in the Grimus–Neufeld model. Pole masses are calculated in three different ways: using the approximation of Grimus and Lavoura, using a one-loop approximation and using FlexibleSUSY, an automated spectrum generator. We present the differences between these calculations and compare them numerically in the parameter region that could potentially reproduce the measured neutrino mass squared differences.

abstract

The understanding of neutrino–nucleus interactions is crucial for the precise measurement of neutrino oscillations phenomenon. Moreover, it is important for Monte Carlo modeling of neutrinos interactions, which at this moment is simplified. For this reason, a variety of cross-section measurements on different target materials and at different neutrino beam energies are performed worldwide. The goal of this paper is to review the recent results from neutrino cross-section measurements from the T2K experiment.

abstract

T2K is a long-baseline experiment built to measure neutrino oscillations. A muon neutrino (anti-neutrino) beam is produced at the J-PARC accelerator complex and sent towards the near detector located 280 meters away from the neutrino source and the far detector at 295 kilometers. The change in the measured intensity and composition of the beam is used to extract the oscillation parameters. The T2K experiment has provided \(2\sigma \) confidence intervals for \(\delta _{\mathrm {CP}}\) phase and improved the precision of the \(\theta _{23}\) and \(\Delta m^2_{32}\) measurement. A summary of the neutrino oscillation results for \(1.49 \times 10^{21}\) POT in neutrino-mode and \(1.63 \times 10^{21}\) POT in anti-neutrino-mode (January 2010–May 2018) is presented.

abstract

The research programme of the NA61 Collaboration covers a wide range of hadronic physics in the CERN SPS energy range, encompassing measurements of hadron–hadron, hadron–nucleus as well as nucleus–nucleus collisions. The latter are analysed to better understand the properties of hot and dense nuclear matter. In this paper, recent results of particle production properties as well as event-by-event fluctuations in proton–proton, as signatures of the critical point of strongly interacting matter, in Be+Be and Ar+Sc interactions at beam energies of 19\(A\)/20\(A\), 30\(A\), 40\(A\), 75\(A\)/80\(A\) and 158\(A\) GeV/\(c\) are presented.

abstract

Our recent investigations of the spin asymmetry observables in the charged current inelastic and quasielastic neutrino (antineutrino)–nucleon scattering are reviewed. The spin asymmetry observables contain full information about the structure of the electroweak neutrino–nucleon vertex. Hence, they can be used to constrain the cross-section models for the single-pion production in \(\nu \)-nucleon scattering and they allow to study the axial content of the nucleon and the second class current contribution to the quasielastic scattering amplitudes.

abstract

The little Higgs model with T-parity, compatible with electroweak precision constraints, introduces new flavor-mixing sources some of which had been ignored until recently. They are reviewed here, showing that their influence does not only enrich the phenomenology of flavor-changing processes but is also needed to render finite one-loop amplitudes.

abstract

We investigate the viability of a simple dark matter (DM) model consisting of a single fermion in the context of galactic dynamics; the model has a single free parameter, the DM mass. We follow an approach similar to the one used in the Thomas–Fermi model of the atom, and find that for the 76 galaxies considered, the model can explain most of the bulk galactic properties provided the DM mass is in the \({\cal {O}}(50\) eV) range. More precise tests of the model require better modeling of the baryon profile, and a better control on the uncertainties in the data.

abstract

In this paper, we discuss possibility of detecting signals of dark matter particles at future \(e^+e^-\) colliders. Two simple models of dark matter are considered, a vector one and a fermion one. Scanning the parameter space of the models, we are seeking regions allowed by current experimental constraints, that maximize cross section for DM production at future \(e^+e^-\) colliders. Could the signal of DM be statistically significant? Would it be possible to determine mass and spin of dark particles? It turns out that the answers depend on the parameters of the model of dark matter — both positive and negative conclusion can be consistent with current experimental data.

abstract

We explore a possibility of dark matter (DM) interacting with the visible sector only through gravity. We consider the case of the vector DM and discuss both perturbative and non-perturbative mechanisms that can be relevant for DM production. In the first case, we investigate particle production during reheating phase via the freeze-in mechanism, while the latter refers to the particle creation in the time-varying background during inflation. In each case, we find a viable range in parameter space which reproduces the observed DM relic abundance.

abstract

We explore the possibility that scale symmetry is a quantum symmetry that is broken only spontaneously in flat space and apply this idea to the Standard Model (SM). The one-loop scalar potential is scale-invariant, since the loop calculations preserve the scale symmetry, with the DR subtraction scale generated spontaneously by the dilaton vacuum expectation value, \(\langle \sigma \rangle \). At the quantum level, the Higgs mass is protected although the theory is non-renormalizable. It is argued that the instability of the effective potential in the Higgs sector that is driven by the quartic coupling running towards negative values becomes worse in the scale-invariant version, since the effective potential becomes unbounded from below.

abstract

Using the gas mass fraction \(f_{\rm gas}\) measurements obtained on the basis of X-ray data for two samples of hot and dynamically relaxed galaxy clusters: 42 clusters with redshifts in the range of \(0.05 \lt z \lt 1.1\) collected and analysed by Allen et al. (2008) and 35 clusters at redshifts \(0.15\lt z\lt 0.30\) selected and analysed by Landry et al. (2013), we obtained constraints on main cosmological parameters in two popular cases: \(w\)CDM model in which dark energy equation of state is constant in time and the model in which dark energy equation of state evolves with redshift according to the Chevalier–Polarski–Linder (CPL) parametrization. Our results from numerical Monte Carlo calculations are following: \({\mit \Omega }_m = 0.3695 ^{+0.1121}_{-0.173}\), \(H_{0} = 66.74 ^{+28.48}_{-42.15}\), \(w = -0.78 ^{+0.1695}_{-0.2615}\) for \(w\)CDM model and \({\mit \Omega }_m = 0.2523 ^{+0.1738}_{-0.0694}\), \(H_{0} = 67.29 ^{+24.27}_{-29.98}\), \(w_0 = -0.86 ^{+0.4541}_{-0.3245}\), \(w_a = 0.6948 ^{+0.5226}_{-0.892}\) for CPL scenario and are in an agreement with the results based on other well-established, independent techniques. This shows that galaxy clusters can be used as a good tool in cosmology. Moreover, we investigate the recent (i.e. at low redshift) expansion history of the Universe finding no evidence that the cosmic acceleration is now slowing down.

abstract

Analysis of the density dependence of the symmetry energy in the case of strangeness-rich neutron star matter has been done. It has been shown that the equation of state which gives the maximum neutron star mass of the order of 2 \(M_\odot \) meets the experimental constraints obtained for the high density limit of the symmetry energy.

abstract

As in boiling super-heated liquid, first-order phase transitions in QFT arise from an abrupt decay of an excited state of false vacuum into an energetically more favorable minimum of energy through bubble nucleation. We review an efficient semi-analytical approach to compute such a tunneling decay rate with any number of scalar fields and space-time dimensions. It is based on exact analytical solutions of piece-wise linear potentials with an arbitrary number of segments that describe any given potential up to the desired precision. Contributions beyond the linear order as well as the generalization to more fields are considered and computed through analytical linear expansions within a few iterations. Thereby, this approach provides a fast and robust method for evaluating tunneling decay in theories with multiple scalar fields.

abstract

We present an idea of how to use a continuous extrapolation of the perturbative results of colour evolution at the amplitude level to the non-perturbative regime. Then we apply it as a guiding principle for a colour reconnection built on top of cluster hadronization model.

abstract

Triggered by ongoing dark matter searches in the \(t\bar {t}+E_{\rm T}^{\rm miss}\) channel, we present state-of-the-art predictions for the Standard Model background process \(pp \to t\bar {t}Z(Z\to \nu \bar {\nu })\) with leptonic top-quark decays. Our calculation is accurate at next-to-leading order in QCD and includes for the first time off-shell and non-resonant effects for the decays of top quarks and heavy bosons. We show predictions for the LHC at 13 TeV for several observables of phenomenological interest, together with a full estimate of the theoretical uncertainties stemming from variation of scales and parton distribution functions.

abstract

In this contribution, we present a detailed study of the effects that decrease the numerical precision in computing QCD radiative corrections to shape distributions at the next-to-next-to-leading order (NNLO) accuracy. For a specific example, we study the contributions to the distribution of soft-dropped heavy-jet mass. We focus on the edge of the phase space where the shape value becomes small and the cross section is dominated by large logarithmic contributions. We use the CoLoRFuLNNLO subtraction method that defines local subtractions in all single and double unresolved regions of the phase space.

abstract

We investigate the single virtual photon–photon scattering into two pions up to 1.5 GeV for the low spacelike virtualities in the dispersive formalism. In order to account for the rescattering effects in both \(S\)- and \(D\)-waves, we adopt the Omnès representation. The unsubtracted dispersion relations describe well the cross-section data and predicts charged pion dipole polarizability \((\alpha _1-\beta _1)_{\pi ^{\pm }}=6.1\times 10^{-4}\) fm\(^3\) consistent with the recent COMPASS measurement and \(\chi \)PT. However, for the neutral pion, the dipole polarizability turns out to be far away from \(\chi \)PT value. In these proceedings, we show how a once-subtracted dispersion relation can potentially cure this problem. Besides, the preliminary error analysis is given.

abstract

Parameterization of amplitudes for two-body interactions is very common and very important link between the experiment itself and the final results of the analysis — e.g. resonance spectrum. There are many methods of parameterization, but only some meet the unitarity condition, which may prove to be crucial in obtaining results, especially when we care about their high precision. It turns out that it is quite easy to ensure that the unitarity condition is fulfilled by amplitude, but amplitudes that break unitarity are very often created and used, especially those for many resonances. Only few conditions must be fulfilled to guarantee unitarity and thus increase the reliability of the obtained results. It is very important presently, when in many data analyses very small, overlapping or broad signals are studied, nonunitary effects can significantly influence results and lead to nonphysical interpretation of obtained parameters.

abstract

We present a recent study of the muon magnetic moment and two lepton-flavour violating observables in the MRSSM. The MRSSM exhibits several key differences compared to the MSSM: there is no \(\tan \beta \) enhancement in \((g-2)\) or \(\mu \to e\gamma \), and the correlation between \(\mu \to e\gamma \) and \(\mu \to e\) conversion is weak in the largest region of parameter space. As a result, the MRSSM can be falsified if the COMET Phase 1 experiment finds a non-vanishing signal.

abstract

We review how the limits on squark masses coming from their direct searches at the Large Hadron Collider change in the non-minimal supersymmetric model. Particularly, we look at the well-motivated SUSY model with a continues \(R\)-symmetry — the so-called Minimal \(R\)-symmetric Supersymmetric Standard Model. We show that, in a scenario with degenerate squark masses and heavy gluino, the squark mass limit is \(m_{\tilde {q}} \gt 1.7\) TeV — approximately 600 GeV lower than in the MSSM.

abstract

The low-energy effective field theory for electroweak (EW) interactions is studied here. It embeds the Standard Model (SM) as a particular limit and parametrizes new physics deviations. We discuss some experimental resonant diboson searches and four-fermion operator analyses that seem to push the new physics scale well over the TeV. On the other hand, the more precise oblique parameter determinations allow new physics resonances in the few TeV range. This apparent contradiction is easily solved by postulating a Standard Model extension that only couples directly to the bosonic degrees of freedom of the Standard Model but not to its fermions.

abstract

The review of the recent developments in the field of radiative corrections and their implementation in the Monte Carlo event generator Phokhara is presented. Furthermore, discussion of the importance of obtained results for future measurements of the hadronic cross section is performed.

abstract

We consider an effective Lagrangian for lepton-flavor violating (LFV) interactions with an additional invisible boson (\(\chi \)). Our most important result is that current and future searches for the \(\ell _i^\pm \to \ell _j^\pm \chi \) decays (with \(i\neq j\) lepton flavors) should not only aim to improve over the old ARGUS bounds (with upper limits \(\sim 5\times 10^{-3}\) on the corresponding \(\tau \to \ell \chi \), \(\ell =e,\mu \) branching fractions) but to reach the \(\lesssim 10^{-7}\) exclusion region. Otherwise, they would not bring in additional restrictions on these LFV interactions beyond what the LFV \(L\to 3\ell \) decays current limits are excluding indirectly.

abstract

The automatic generation of multichannel Monte Carlo phase-space integration routines of carlomat, which up to now took into account only mappings of \(\sim 1/s\) or Breit–Wigner behaviour of the \(s\)-channel diagrams, is being supplemented with the parameterizations which map away the \(t\)-channel, soft and collinear photon or gluon emission. In order to improve numerical stability, the quadruple precision versions of the routines for computation of the helicity amplitudes and phase-space parameterizations have been written and calls to them are being implemented in the code generation part of the program.

abstract

Accurate theoretical predictions in the Standard Model (SM) are vital to disentangle possible new physics effects. The loop–tree duality (LTD) formalism transforms the integration domain of loop scattering amplitudes to a Euclidean space where asymptotic expansions of the integrand are well defined. The effectiveness of LTD for making asymptotic expansions has been shown in the large-mass and small-mass limits for Higgs production through gluon fusion. In this paper, we present a preliminary study aimed at generalising the method of asymptotic expansions in the LTD formalism. We use a toy amplitude and derive general guidelines.

abstract

The status of numerical evaluations of Mellin–Barnes integrals is discussed, in particular the application of the quasi-Monte Carlo integration method to the efficient calculation of multidimensional integrals.

abstract

The Cosmic-Ray Extremely Distributed Observatory (CREDO) is a project created a few years ago in the Institute of Nuclear Physics PAS in Kraków and dedicated to global studies of extremely extended cosmic-ray phenomena. The main reason for creating such a project was that the cosmic-ray ensembles (CRE) are beyond the capabilities of existing detectors and observatories. Until now, cosmic ray studies, even in major observatories, have been limited to the recording and analysis of individual air showers, therefore, ensembles of cosmic-rays, which may spread over a significant fraction of the Earth were neither recorded nor analyzed. In this paper, the status and perspectives of the CREDO project are presented.