SMEFTsim 3.0 — a practical guide

The SMEFTsim package [1] is designed to enable automated computations in the Standard Model Effective Field Theory (SMEFT), where the SM Lagrangian is extended with a complete basis of dimension six operators. It contains a set of models written in FeynRules and pre-exported to the UFO format, for usage within Monte Carlo event generators. The models differ in the flavor assumptions and in the input parameters chosen for the electroweak sector. The present document provides a self-contained, pedagogical reference that collects all the theoretical and technical aspects relevant to the use of SMEFTsim and it documents the release of version 3.0. Compared to the previous release, the description of Higgs production via gluon-fusion in the SM has been significantly improved, two flavor assumptions for studies in the top quark sector have been added, and a new feature has been implemented, that enables the treatment of linearized SMEFT corrections to the propagators of unstable particles.SMEFTsim 3.0 is available on the Github website https://SMEFTsim.github.io and on the FeynRules database http://feynrules.irmp.ucl.ac.be/wiki/SMEFT.

CP violation in mixing and oscillations in a toy model for leptogenesis with quasi-degenerate neutrinos

We study the sources of CP violation for baryogenesis models with quasi-degenerate neutrinos. Our approach is to use the renormalized propagator in a quantum field theory model of neutrino oscillations, paying close attention to unitarity requirements. From the probabilities of lepton number violating processes obtained in this way, we derive a source term for the time evolution of the lepton asymmetry. The source term has contributions that can be identified with CP violation from mixing, oscillations and interference between both. Given that this source term does not involve processes with unstable particles in the initial or final states, neither does it require to calculate number densities of neutrinos, no subtraction of real intermediate states must be performed. In equilibrium the source term is null, as demanded by unitarity and CPT invariance, due to a cancellation between the terms coming from CP violation in mixing and oscillations. The calculations are done in a simple scalar toy model, and the resummed propagator is diagonalized at first order in the decay widths over the mass difference. We also comment on the effect of the interference term, which is mild at the order we work, but seems to become more important with increasing degeneracy.

Degradable and colloidally stable zwitterionic-functionalized silica nanoparticles

Aim: This work is focused on obtaining degradable mesoporous silica nanoparticles (DMSNs) which are able to maintain their colloidal stability in complex biological media. Materials & methods: DMSNs were synthesized using different ratios of disulfide organosilane (degradable structural moiety) and further functionalized with sulfobetaine silane (SBS) to enhance colloidal stability and improve biological compatibility. Results: There was a clear trade-off between nanoparticle degradability and colloidal stability, since full optimization of the degradation process generated unstable particles, while enhancing colloidal stability resulted in poor DMSNs degradation. It was also shown that acidic pH improved particle degradation which is commonly triggered by reduction stimulus. Conclusion: A chemical composition window was found where DMSNs presented satisfactory colloidal stability in biologically relevant medium, meaningful degradation profiles and high biocompatibility.

On the hydrodynamics of unstable excitations

The generalized hydrodynamic (GHD) approach has been extremely successful in describing the out-of-equilibrium properties of a great variety of integrable many-body quantum systems. It naturally extracts the large-scale dynamical degrees of freedom of the system, and is thus a particularly good probe for emergent phenomena. One such phenomenon is the presence of unstable particles, traditionally seen via special analytic structures of the scattering matrix. Because of their finite lifetime and energy threshold, these are especially hard to study. In this paper we apply the GHD approach to a model possessing both unstable excitations and quantum integrability. The largest family of relativistic integrable quantum field theories known to have these features are the homogeneous sine-Gordon models. We consider the simplest non-trivial example of such theories and investigate the effect of an unstable excitation on various physical quantities, both at equilibrium and in the non-equilibrium state arising from the partitioning protocol. The hydrodynamic approach sheds new light onto the physics of the unstable particle, going much beyond its definition via the analytic structure of the scattering matrix, and clarifies its effects both on the equilibrium and out-of-equilibrium properties of the theory. Crucially, within this dynamical perspective, we identify unstable particles as finitely-lived bound states of co-propagating stable particles of different types, and observe how stable populations of unstable particles emerge in large-temperature thermal baths.

MUON INTENSITY VARIATIONS AND ATMOSPHERIC TEMPERATURE

Muons in the atmosphere are formed during the decay of pions resulting from nuclear interactions of cosmic rays with nuclei of air atoms. The resulting muons are also unstable particles with a short lifetime. Therefore, not all of them reach the level of observation in the atmosphere. When the atmospheric temperature changes, the distance to the observation level changes too, thus leading to variations in the intensity of muons of temperature origin. These variations, caused by atmospheric temperature variations, are superimposed on continuous observations of muon telescopes. Their exclusion is, therefore, extremely necessary, especially in the data from modern muon telescopes whose statistical accuracy is very high. The contribution of various atmospheric layers to the total temperature effect is not the same for muons. This contribution is characterized by the distribution of the density of temperature coefficients for muons in the atmosphere. Using this distribution and the continuous intensity observations from the muon telescope in Novosibirsk, the inverse problem has been solved, from the solution of which the atmospheric temperature variations over a long period from 2004 to 2011 have been found. The results obtained are compared with aerological sounding data.

MUON INTENSITY VARIATIONS AND ATMOSPHERIC TEMPERATURE

Muons in the atmosphere are formed during the decay of pions resulting from nuclear interactions of cosmic rays with nuclei of air atoms. The resulting muons are also unstable particles with a short lifetime. Therefore, not all of them reach the level of observation in the atmosphere. When the atmospheric temperature changes, the distance to the observation level changes too, thus leading to variations in the intensity of muons of temperature origin. These variations, caused by atmospheric temperature variations, are superimposed on continuous observations of muon telescopes. Their exclusion is, therefore, extremely necessary, especially in the data from modern muon telescopes whose statistical accuracy is very high. The contribution of various atmospheric layers to the total temperature effect is not the same for muons. This contribution is characterized by the distribution of the density of temperature coefficients for muons in the atmosphere. Using this distribution and the continuous intensity observations from the muon telescope in Novosibirsk, the inverse problem has been solved, from the solution of which the atmospheric temperature variations over a long period from 2004 to 2011 have been found. The results obtained are compared with aerological sounding data.