Standard Model Interactions Research Articles

Dirac leptogenesis from asymmetry wash-in via scatterings

Leptogenesis typically requires the introduction of heavy particles whose out-of-equilibrium decays are essential for generating a matter-antimatter asymmetry, according to one of Sakharov’s conditions. We demonstrate that in Dirac leptogenesis, scatterings between the light degrees of freedom—Standard Model particles plus Dirac neutrinos—are sufficient to generate the asymmetry. The generation requires at least two effective charges conserved by the fast Standard Model interactions. Due to its vanishing source term in the Boltzmann equations, the asymmetry of right-handed neutrinos solely arises through wash-in processes. Sakharov’s conditions are satisfied because the right-handed neutrino partners are out of equilibrium. Consequently, heavy degrees of freedom never needed to be produced in the early universe, allowing for a reheating temperature well below their mass scale. Considering a minimal leptoquark model, we discuss the viable parameter space along with the potential observational signature of an increased number of effective neutrinos in the early universe. Published by the American Physical Society 2024

New constraints on CPT symmetry violation in charm mesons

Small CPT-violating effects are admissible in several theories beyond the Standard Model of interactions. We analyze experimental data obtained with neutral flavored meson mixing and place bounds on the scale of such phenomena. The constraints on the CPT-violating parameter z are derived by reinterpreting the LHCb measurement of the time-dependent asymmetry in the Cabbibo-favored D0→K−π+ and D0¯→K+π− decay rates. The bounds provided in this paper are 2 orders of magnitude stricter compared to the results obtained by the FOCUS Collaboration. Among other constraints, we report bounds on the differences in the decay widths and masses of the neutral D meson flavor states at a 95% confidence level. The decay width difference is bounded by (−4.7<δΓD<2.1)×10−16 GeV. The mass difference lies within (−2.0<δmD<2.0)×10−15 GeV for 95% of arg(z) values. The paper includes an assessment of the influence of CP violation on the results and a discussion of the future prospects. Published by the American Physical Society 2024

Constraining the mass-spectra in the presence of a light sterile neutrino from absolute mass-related observables

The framework of three-flavor neutrino oscillation is a well-established phenomenon, but results from the short-baseline experiments, such as the Liquid Scintillator Neutrino Detector (LSND) and MiniBooster Neutrino Experiment (MiniBooNE), hint at the potential existence of an additional light neutrino state characterized by a mass-squared difference of approximately 1 eV2. The new neutrino state is devoid of all Standard Model (SM) interactions, commonly referred to as a “sterile” state. In addition, a sterile neutrino with a mass-squared difference of 10−2 eV2 has been proposed to improve the tension between the results obtained from the Tokai to Kamioka (T2K) and the NuMI Off-axis νe Appearance (NOνA) experiments. Further, the nonobservation of the predicted upturn in the solar neutrino spectra below 8 MeV can be explained by postulating an extra light sterile neutrino state with a mass-squared difference around 10−5 eV2. The hypothesis of an additional light sterile neutrino state introduces four distinct mass spectra depending on the sign of the mass-squared difference. In this paper, we discuss the implications of the above scenarios on the observables that depend on the absolute mass of the neutrinos; namely, the sum of the light neutrino masses (Σ) from cosmology, the effective mass of the electron neutrino from beta decay (mβ), and the effective Majorana mass (mββ) from neutrinoless double beta decay. We show that some scenarios can be disfavored by the current constraints of the above variables. The implications for projected sensitivity of Karlsruhe Tritium Neutrino Experiment (KATRIN) and future experiments like Project-8, next Enriched Xenon Observatory (nEXO) are discussed. Published by the American Physical Society 2024

EFT, decoupling, Higgs boson mixing, and higher dimensional operators

The effective field theory (EFT) framework is a precise approximation procedure when the inherent assumptions of a large-scale separation between the Standard Model (SM) and new interactions alongside perturbativity are realized. Constraints from available data might not automatically guarantee these circumstances when contrasted with UV scenarios that the EFT analysis wishes to inform. From an EFT perspective, achieving sufficient precision in navigating the alignment or decoupling limits beyond the SM scenarios can necessitate moving beyond the SM’s leading, dimension six EFT deformation. Using the example of Higgs boson mixing, we demonstrated the importance of higher-dimensional terms in the EFT expansion. We analyze the relevance of virtual EFT corrections and dimension eight contributions for well-determined electroweak precision observables. We find that when moving away from the decoupling limit, the relevance of additional terms in the EFT expansion quickly becomes relevant. This demonstrates the necessity to move beyond dimension six interactions for any scenario that contains Higgs boson mixing. Published by the American Physical Society 2024

Gravitational decoherence by the apparatus in the quantum-gravity-induced entanglement of masses

Abstract One of the outstanding questions in modern physics is how to test whether gravity is classical or quantum in a laboratory. Recently there has been a proposal to test the quantum nature of gravity by creating quantum superpositions of two nearby neutral masses, close enough that the quantum nature of gravity can entangle the two quantum systems, but still sufficiently far away that all other known Standard Model interactions remain negligible. However, preparing superposition states of a neutral mass (the light system) requires the vicinity of laboratory apparatus (the heavy system). We will suppose that such a heavy system can be modelled as another quantum system; since gravity is universal, the lighter system can get entangled with the heavier system, providing an inherent source of gravitational decoherence. In this paper, we will consider a toy model composed of two light and two heavy quantum oscillators prepared in the motional ground state, forming pairs of probe-detector systems, and study under what conditions the entanglement between two light systems evades the decoherence induced by the heavy systems. We conclude by estimating the decoherence in the proposed experiment for testing the quantum nature of gravity.

Dixon-Rosenfeld lines and the Standard Model

We present three new coset manifolds named Dixon-Rosenfeld lines that are similar to Rosenfeld projective lines except over the Dixon algebra mathbb {C}otimes mathbb {H}otimes mathbb {O}. Three different Lie groups are found as isometry groups of these coset manifolds using Tits’ formula. We demonstrate how Standard Model interactions with the Dixon algebra in recent work from Furey and Hughes can be uplifted to tensor products of division algebras and Jordan algebras for a single generation of fermions. The Freudenthal–Tits construction clarifies how the three Dixon-Rosenfeld projective lines are contained within mathbb {C}otimes mathbb {H}otimes J_{2}(mathbb {O}), mathbb {O}otimes J_{2}(mathbb {C}otimes mathbb {H}), and mathbb {C}otimes mathbb {O}otimes J_{2}(mathbb {H}).

LePDF: Standard Model PDFs for high-energy lepton colliders

The emission of collinear radiation off an elementary lepton can be factorised from the hard scattering process by introducing Parton Distribution Functions of a Lepton (LePDF), which, contrary to protons, can be derived from first principles. In case of multi-TeV lepton colliders, such as the muon colliders currently being proposed, the complete structure of Standard Model interactions must be taken into account. In this work we solve numerically the corresponding DGLAP equations at the double-log order and provide public files with LePDFs for both muons and electrons, including polarisation effects. We discuss several interesting aspects of the resulting PDFs and compare them with the Effective Vector Approximation, showing that the latter fails to describe well the vector bosons PDFs at small momentum fractions, unless it is extended to higher orders.

A combinatorial derivation of the standard model interactions from the Dirac Lagrangian

A composite model of the standard model particles was recently derived using the Dirac Lagrangian on a spacetime where time does not advance along the worldlines of fundamental dust particles, called an ‘internal spacetime’. The aim of internal spacetime geometry is to model certain quantum phenomena using (classical) degenerate spacetime metrics. For example, on an internal spacetime, tangent spaces have variable dimensions, and spin wavefunction collapse is modeled by the projection from one tangent space to another. In this article, we show that the combinatorial structure of the internal Dirac Lagrangian yields precisely the standard model trivalent vertices, together with two new additional (longitudinal) [Formula: see text] vertices that generate the four-valent boson vertices. In particular, we are able to derive electroweak parity violation for both leptons and quarks. We also obtain new restrictions on the possible spin states that can occur in certain interactions. Finally, we determine the trivalent vertices of the new massive spin-[Formula: see text] boson predicted by the model.

Proposal and Analysis of an Experiment for Accurate Measurement of the Muon Lifetime and the Fermi Constant

An experiment is proposed for a record-breaking measurement of the world Fermi constant GF during the decay of a positive muon. All systematic errors were analyzed. The Fast Program (FP) was developed and tested using the GEANT data and running ≈1500 times faster. 1014 events were collected with two options for selecting events. An accuracy of 0.46 ps for the muon lifetime and 0.1 ppm for the GF value was obtained taking into account all systematic errors. The accuracy of the theoretical calculations of GF is 0.14 ppm within the framework of the Standard Model interactions of elementary particles

Sculpting the Standard Model from low-scale gauge-Higgs-matter E8 grand unification in ten dimensions

The construction and general implications of a model with complete supersymmetric unification of the Standard Model matter content, interactions and families' replication into a single E8 gauge superfield in ten dimensions is presented. The gauge and extended Poincaré symmetries are broken through compactification of the T6/(Z3×Z3) orbifold with Wilson lines, which reduces the original symmetry and matter content into those of the Standard Model plus additional heavier states. Proton decay can be suppressed automatically while the compactification scale may be as low as 109GeV, so that the corresponding GUT-scale physics may be potentially accessible and testable by future collider measurements.

Impact of ATLAS constraints on effective dark matter-standard model interactions with spin-one mediators

We complement a previous work [Fabiola Fortuna et al., Effective field theory analysis of dark matter-standard model interactions with spin one mediators, J. High Energy Phys. 02 (2021) 223.] using an effective field theory framework of dark matter and standard model interactions, with spin-one mediators, exploring a wider dark matter mass range, up to 6.4 TeV. We again use bounds from different experiments: relic density, direct detection experiments, and indirect detection limits from the search of gamma-ray emissions and positron fluxes. Additionally, in this paper we add collider constraints by the ATLAS Collaboration in the monojet analysis. Moreover, here we tested our previous results in the light of the aforementioned ATLAS data, which turns out to be the most restrictive for light dark matter masses (as expected), ${m}_{\mathrm{DM}}<{M}_{Z}/2$. We obtain a larger range of solutions for the operators of dimension 5, OP1 and OP4, where masses above 43 GeV and 30 GeV [except for the $Z$-resonance region, $\ensuremath{\sim}({M}_{Z}\ifmmode\pm\else\textpm\fi{}{\mathrm{\ensuremath{\Gamma}}}_{Z})/2$], respectively, are allowed. In contrast, the operator of dimension 6, OP3, has viable solutions for masses $\ensuremath{\gtrsim}190\text{ }\text{ }\mathrm{GeV}$. For the combination of OP1 and OP3 we obtain solutions (for masses larger than 140 GeV or 325 GeV) that depend on the relative sign between the operators.

Elementary particle non-perturbative mass generation. A step towards a beyond-the-Standard-Model model

We show that a recently discovered non-perturbative field-theoretical mechanism giving mass to elementary fermions, is also capable of generating a mass for the weak bosons, when the model is extended to encompass weak interactions, and can thus be used as a viable alternative to the Higgs scenario. A detailed analysis of this remarkable feature shows that the non-perturbatively generated fermion and W masses have the parametric form mf∼Cf(α)ΛRGI and MW∼gwcw(α)ΛRGI, respectively, where the coefficients Cf(α) and cw(α) are functions of the gauge couplings, gw is the weak coupling and ΛRGI is the RGI scale of the theory. In view of these expressions, we see that to match the experimental values of the top quark and W masses, we are led to conjecture the existence of a yet unobserved sector of massive fermions (that we denote Tera-fermions) subjected, besides ordinary Standard Model interactions, to a super-strong gauge interactions (Tera-interactions), so that the full theory (SM plus Tera-particles) will have an RGI scale ΛRGI≡ΛT≫ΛQCD in the TeV region. This approach offers a solution of the Higgs mass naturalness problem (there is no fundamental Higgs), an understanding of the fermion mass hierarchy and a physical interpretation of the electro-weak scale as a fraction of ΛT.

Search for upward-going showers with the Pierre Auger Observatory

Motivated by the ANITA report of pulses compatible with upward-going extensive air showers, we present a recent search for such showers using the Pierre Auger Observatory. The dataset, registered using the fluorescence detector of the Observatory, is scanned to identify showers ascending from the ground. Consistent with the exit angles reported from the first and third ANITA flights, we focus on shower geometries that are incompatible with Standard Model interactions of neutrinos in the Earth. We present the effective area of the Observatory to generic upward-going showers as a function of shower energy and altitude. This can be used to constrain predictions based on physics beyond Standard Model and the upgoing-shower interpretation of the ANITA results. To demonstrate the method, we calculate limits to the production rate of tau leptons near the ground emerging under a range of exit angles.

MUonE, muon g−2 and electroweak precision constraints within 2HDMs

Two Higgs doublet models are attractive scenarios for physics beyond the Standard Model. In particular, lepton-specific manifestations remain contenders to explain the observed discrepancy between the anomalous magnetic moment of the muon $a_\mu$ predicted within the Standard Model and recent observations at Fermilab and BNL. Dominant uncertainties that affect $a_\mu$ have motivated the MUonE experiment to access the hadronic vacuum polarisation contribution that impacts $a_\mu$ via elastic muon-electron scattering. In this work, we contrast the high precision that is achievable within the MUonE context with constraints from flavour physics, precision electroweak constraints and LHC searches as well as their extrapolations for a range of two Higgs doublet models with a softly broken $\mathbb{Z}_2$ symmetry. We find that the sensitivity of MUonE does not extend beyond the parameter regions that are already excluded by other constraints. MUonE will therefore provide a detailed measurement of the hadronic vacuum polarisation contribution which then transparently informs $a_\mu$ interpretations in 2HDMs without modifications of correlations from beyond the Standard Model interactions. In passing we extend earlier results of LHC and flavour projections to lepton-specific 2HDM (Types X and Y) scenarios, and comment on the possibility of modifying the value of the W-boson mass; we briefly discuss the implications for a strong first-order electroweak phase transition for these models.

One-loop corrections for WW to HH in Higgs EFT with the electroweak chiral Lagrangian

In this work we present the computation of the one-loop electroweak radiative corrections to the scattering process $WW\to HH$ within the context of the Higgs Effective Field Theory (HEFT). We assume that the fermionic interactions are like in the Standard Model, whereas the Beyond Standard Model interactions in the bosonic sector are given by the Electroweak Chiral Lagrangian. The computation of the one-loop amplitude and the renormalization program is performed in terms of the involved one-particle-irreducible functions (1PI) and using $R_\xi$ covariant gauges. The renormalization of 1PI functions at arbitrary external momenta is a more ambitious program than just renormalizing the amplitude with on-shell external legs and it has the advantage that they can be used in several scattering amplitudes. In fact, we use here some of the 1PI functions already computed in our previous work (devoted to $WZ \to WZ$). We will complement them here with the computation of the new 1PI functions required for $WW \to HH$. From this renormalization procedure we will also derive the full set of renormalized coefficients of the EChL that are relevant for this scattering process. In the last part, we will present the numerical results for the EChL predictions of the one-loop level cross section, $\sigma(WW \to HH)|_{\rm 1-loop}$, as a function of the center of mass energy, showing the relative size of the one-loop radiative corrections respect to the tree level prediction in terms of the EChL coefficients. The results of the one-loop corrections to $WW \to HH$ for the SM case will be also presented, for comparison with the EChL case, following the same computational method, i.e., by means of the renormalization of 1PI functions.

Leptons and other forces of nature

Assuming that neutrinos are not Majorana fermions and the right handed Dirac neutrino does not exist, we propose a model in which the second and the third generations of the leptons are composites, while the first generation is fundamental. The composite states are formed by the fundamental leptons and two new fundamental hidden scalar particles. In addition, there exist two hidden forces besides the standard model interactions. The gauge symmetry SU(2) L ⊗ U(1) Y ⊗ U(1) h ⊗ SU(2) h of the electroweak and the hidden forces breaks down to U(1) Y ⊗ U(1) h after the spontaneous symmetry breaking. We explain the neutrino masses in terms of the binding dynamics of a hidden force. The phenomenon of neutrino oscillation can also be explained by our model in a dynamical framework of the hidden forces.

Sensitivity of accelerator-based neutrino experiments to neutrino-dark matter interaction: Elko as a viable dark matter candidate

We analyze the potential of accelerator-based neutrino experiments, such as the Deep Underground Neutrino Experiment, to constrain a five-dimensional operator mediating a beyond standard model interaction between a mass-dimension-one fermion field, labeled elko, and neutrino. We identify the parameter space where elko is a viable dark matter candidate.

Coloring mixed QCD/QED evolution

Parton showers are crucial components of high-energy physics calculations. Improving their modelling of QCD is an active research area since shower approximations are stumbling blocks for precision event generators. Naively, the interference between sub-dominant Standard-Model interactions and QCD can be of similar size to subleading QCD corrections. This article assesses the impact of QCD/QED interference effects in parton showers, by developing a sophisticated shower including QED, QCD at fixed color, and employing complete tree-level matrix element corrections for individual N_C=3NC=3 color configurations to embed interference. The resulting simulation indicates that QCD/QED interference effects are small for a simple test case and dwarfed by electro-weak resonance effects.

Detecting beyond the standard model interactions of solar neutrinos in low-threshold dark matter detectors

As low-threshold dark matter detectors advance in development, they will become sensitive to recoils from solar neutrinos which opens up the possibility to explore neutrino properties. We predict the enhancement of the event rate of solar neutrino scattering from Beyond the Standard Model interactions in low-threshold DM detectors, with a focus on silicon, germanium, gallium arsenide, xenon, and argon-based detectors. We consider a set of general neutrino interactions, which fall into five categories: the neutrino magnetic moment as well as interactions mediated by four types of mediators (scalar, pseudoscalar, vector, and axial vector), and consider coupling these mediators to either quarks or electrons. Using these predictions, we place constraints on the mass and couplings of each mediator and the neutrino magnetic moment from current low-threshold detectors like SENSEI, Edelweiss, and SuperCDMS, as well as projections relevant for future experiments such as DAMIC-M, Oscura, Darwin, and ARGO. We find that such low-threshold detectors can improve current constraints by up to two orders of magnitude for vector mediators and one order of magnitude for scalar mediators.

Review on Higgs Hidden–Dark Sector Physics at High-Energy Colliders

The presence of a hidden or dark sector of phenomena that relates either weakly or in a particular way to Standard Model (SM) fields has theoretical as well as experimental support. Many extensions of SM use hidden or dark sector states to propose a specific candidate for dark matter (DM) in the universe or to explain astrophysical findings. If such a family of Beyond the Standard Model (BSM) particles and interactions exists, it is possible that they will be discovered experimentally at CERN’s Large Hadron Collider (LHC, s≅ 14 TeV) and future High Energy Colliders. The primary emphasis is on a few examples of searches undertaken at the LHC that are relevant to Higgs Hidden–Dark Sector Physics. These studies’ existing constraints and prospects are also reported.