Neutrinos, being the only fermions in the Standard Model of Particle Physics that do not possess electromagnetic or color charges, have the unique opportunity to communicate with fermions outside the ...Standard Model through mass mixing. Such Standard Model-singlet fermions are generally referred to as “sterile neutrinos”. In this review article, we discuss the theoretical and experimental motivation for sterile neutrinos, as well as their phenomenological consequences. With the benefit of hindsight in 2020, we point out potentially viable and interesting ideas. We focus in particular on sterile neutrinos that are light enough to participate in neutrino oscillations, but we also comment on the benefits of introducing heavier sterile states. We discuss the phenomenology of eV-scale sterile neutrinos in terrestrial experiments and in cosmology, we survey the global data, and we highlight various intriguing anomalies. We also expose the severe tension that exists between different data sets and prevents a consistent interpretation of the global data in at least the simplest sterile neutrino models. We discuss non-minimal scenarios that may alleviate some of this tension. We briefly review the status of keV-scale sterile neutrinos as dark matter and the possibility of explaining the matter–antimatter asymmetry of the Universe through leptogenesis driven by yet heavier sterile neutrinos.
Positronium (Ps) is an exotic hydrogenic atom composed of an electron bound to a positron via the Coulomb force. Being composed of two low-mass leptons, positronium is, for all practical purposes, ...fully described by quantum electrodynamics (QED). The absence of hadronic components suggests that positronium energy levels and decay rates can be calculated to very high precision, limited only by the order of the corresponding perturbative expansion and the tiny effects of heavy or weakly interacting virtual particles and exotic decay modes. Moreover, as it is a low-mass particle–antiparticle system, the QED description of positronium is strongly affected by annihilation and recoil effects that are either weaker or not present in other atoms. As a result, sufficiently precise measurements of Ps energy levels and decay properties can serve as stringent tests of bound-state QED theory, and may be sensitive to processes not present in the theory, such as axion-like particles (beyond the QCD axion), or a fifth fundamental force. In addition, since positronium is an eigenstate of the fundamental symmetries C and P, various symmetry violating mechanisms can be probed through searches for anomalous decay modes. In the last three decades, there have been significant experimental advances in positron and positronium physics which open up the possibility to test QED bound-state theory with unprecedented precision. Here we present the current state-of-the-art in experimental positronium spectroscopy, and discuss explicitly how such measurements can be used to test bound-state QED theory, and how such tests may contribute to the search for physics beyond the Standard Model.
SModelS is an automatized tool enabling the fast interpretation of simplified model results from the LHC within any model of new physics respecting a Z2 symmetry. With the version 1.2 we announce ...several new features. First, previous versions were restricted to missing energy signatures and assumed prompt decays within each decay chain. SModelSv1.2 considers the lifetime of each Z2-odd particle and appropriately takes into account missing energy, heavy stable charged particle and R-hadron signatures. Second, the current version allows for a combination of signal regions in efficiency map results whenever a covariance matrix is available from the experiment. This is an important step towards fully exploiting the constraining power of efficiency map results. Several other improvements increase the user-friendliness, such as the use of wildcards in the selection of experimental results, and a faster database which can be given as a URL. Finally, smodelsTools provides an interactive plots maker to conveniently visualize the results of a model scan.
Program Title: SModelS
Program Files doi:http://dx.doi.org/10.17632/w4nft4459w.2
Licensing provisions: GPLv3
Programming language: Python3
Journal reference of previous version: Comput. Phys. Commun. 227 (2018) 72
Does the new version supersede the previous version?: Yes
Reasons for the new version: Addition of new features.
Summary of revisions: The most important new features in v1.2 are the combination of signal regions in efficiency map results whenever a covariance matrix is available from the experiment, and the implementation of heavy stable charged particle and R-hadron signatures. Moreover, the database of experimental results can now be given as a URL, and the pickling has been improved to make the database faster. Other improvements include that wildcards are allowed when selecting analyses, datasets or topologies, and that the path to the model file, formerly required to be smodels/sparticles.py, can be specified in the parameters card. For the convenience of the user, we also provide a tool to make interactive plots to visualize the results of a model scan. Finally, the whole code now also runs with Python3, which has become the recommended default, and it can now be installed in its source directory.
Nature of problem: The results for searches for new physics beyond the Standard Model (BSM) at the Large Hadron Collider are often communicated by the experimental collaborations in terms of constraints on so-called simplified models spectra (SMS). Understanding how SMS constraints impact a realistic new physics model, where possibly a multitude of production channels and decay modes are relevant, is a non-trivial task.
Solution method: We exploit the notion of simplified models to constrain full models by “decomposing” them into their SMS components. A database of SMS results obtained from the official results of the ATLAS and CMS collaborations, but in part also from ‘recasting’ the experimental analyses, can be matched against the decomposed model, resulting in a statement to what extent the model at hand is in agreement or contradiction with the experimental results. Further useful information on, e.g., the coverage of the model’s signatures is also provided.
Additional comments including restrictions and unusual features: At present, only models with a Z2-like symmetry can be tested. Each SMS is defined purely by the vertex structure and the final-state particles; initial and intermediate BSM particles are described only by their masses, production cross sections, branching ratios and total widths. Possible differences in signal selection efficiencies arising, e.g., from different production mechanisms or from the spin of the BSM particles, are ignored in this approach. Since only part of the full model can be constrained by SMS results, SModelS will always remain more conservative (though orders of magnitude faster) than “full recasting” approaches.
1 F. Ambrogi et al., “SModelS v1.1 user manual: Improving simplified model constraints with efficiency maps,” Comput. Phys. Commun. 227 (2018) 72 arXiv:1701.06586 hep-ph.
We present a new version of PyR@TE, a Python tool for the computation of renormalization group equations for general, non-supersymmetric gauge theories. Its new core relies on a recent paper by Poole ...& Thomsen (2019) to compute the β-functions. In this framework, gauge kinetic mixing is naturally implemented, and the Weyl consistency relations between gauge, quartic and Yukawa couplings are automatically satisfied. One of the main new features is the possibility for the user to compute the gauge coupling β-functions up to the three-loop order. Large parts of the PyR@TE code have been rewritten and improved, including the group theory module PyLie. As a result, the overall performance in terms of computation speed was drastically improved and the model file is more flexible and user-friendly.
Program Title: PyR@TE 3
CPC Library link to program files:https://doi.org/10.17632/8h454kdd5n.2
Licensing provisions: Apache 2.0
Programming language: Python 3
Journal reference of previous version: PyR@TE 1, PyR@TE 2 2
Does the new version supersede the previous version?: Yes.
Reasons for new version: The software was essentially rewritten and new functionalities were added. The performance in terms of computation speed was improved by a factor of 100 to 10000 compared to the previous version. The code now relies on Python 3 instead of the deprecated Python 2.
Summary of revisions: The core of the software was rewritten, based on a new formalism. One of the major new features is the possibility of computing the 3-loop RGEs for gauge couplings. The structure and the syntax of the model file were enhanced. The output of the software was improved.
Nature of problem : Computing the renormalization group equations for any renormalizable, 4-dimensional, non-supersymmetric quantum field theory.
Solution method: Group theory, tensor algebra.
References:
1 F. Lyonnet, I. Schienbein, F. Staub, A. Wingerter, PyR@TE: Renormalization group equations for general gauge theories 185 (3) 1130–1152. http://dx.doi.org/10.1016/j.cpc.2013.12.002.
2 F. Lyonnet, I. Schienbein, PyR@TE 2: A Python tool for computing RGEs at two-loop 213 181–196. http://dx.doi.org/10.1016/j.cpc.2016.12.003.
We present an up-to-date review of Big Bang Nucleosynthesis (BBN). We discuss the main improvements which have been achieved in the past two decades on the overall theoretical framework, summarize ...the impact of new experimental results on nuclear reaction rates, and critically re-examine the astrophysical determinations of light nuclei abundances. We report then on how BBN can be used as a powerful test of new physics, constraining a wide range of ideas and theoretical models of fundamental interactions beyond the standard model of strong and electroweak forces and Einstein’s general relativity.
We consider the role of precision measurements of beta decays and light meson semi-leptonic decays in probing physics beyond the Standard Model in the LHC era. We describe all low-energy ...charged-current processes within and beyond the Standard Model using an effective field theory framework. We first discuss the theoretical hadronic input which in these precision tests plays a crucial role in setting the baseline for new physics searches. We then review the current and upcoming constraints on the various non-standard operators from the study of decay rates, spectra, and correlations in a broad array of light-quark systems. We finally discuss the interplay with LHC searches, both within models and in an effective theory approach. Our discussion illustrates the independent yet complementary nature of precision beta decay measurements as probes of new physics, showing them to be of continuing importance throughout the LHC era.
SModelS is an automatized tool for the interpretation of simplified model results from the LHC. It allows to decompose models of new physics obeying a Z2 symmetry into simplified model components, ...and to compare these against a large database of experimental results. The first release of SModelS, v1.0, used only cross section upper limit maps provided by the experimental collaborations. In this new release, v1.1, we extend the functionality of SModelS to efficiency maps. This increases the constraining power of the software, as efficiency maps allow to combine contributions to the same signal region from different simplified models. Other new features of version 1.1 include likelihood and χ2 calculations, extended information on the topology coverage, an extended database of experimental results as well as major speed upgrades for both the code and the database. We describe in detail the concepts and procedures used in SModelS v1.1, explaining in particular how upper limits and efficiency map results are dealt with in parallel. Detailed instructions for code usage are also provided.
Program Title: SModelS
Program Files doi:http://dx.doi.org/10.17632/w4nft4459w.1
Licensing provisions: GPLv3
Programming language: Python
Nature of problem: The results for searches for new physics beyond the Standard Model (BSM) at the Large Hadron Collider are often communicated by the experimental collaborations in terms of constraints on so-called simplified models spectra (SMS). Understanding how SMS constraints impact a realistic new physics model, where possibly a multitude of relevant production channels and decay modes are relevant, is a non-trivial task.
Solution method: We exploit the notion of simplified models to constrain full models by “decomposing” them into their SMS components. A database of SMS results obtained from the official results of the ATLAS and CMS collaborations, but in part also from ‘recasting’ the experimental analyses, can be matched against the decomposed model, resulting in a statement to what extent the model at hand is in agreement or contradiction with the experimental results. Further useful information on, e.g., the coverage of the models’ signatures is also provided.
Additional comments including Restrictions and Unusual features: At present, the tool is limited to signatures with missing transverse energy, and only models with a Z2-like symmetry can be tested. Each SMS is defined purely by the vertex structure and the SM final state particles; BSM particles are described only by their masses, production cross sections and branching ratios. Possible differences in signal selection efficiencies arising, e.g., from different production mechanisms or from the spin of the BSM particles, are ignored in this approach. Since only part of the full model can be constrained by SMS results, SModelS will always remain more conservative (though orders of magnitude faster) than “full recasting” approaches.
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