We show that the entanglement observed in top-antitop quark spin states at the LHC is local in the energy region close to the production threshold. In contrast, nonlocal entanglement is observed in the central boosted region defined by a top-quark pair invariant mass $${m}_{t\overline{t} }&gt;{8}00$$ GeV and scattering angles Θ satisfying |cos Θ| $\textit{<}$ 0$\textit{.}$2. This makes top-quark pairs a unique laboratory for studying the interplay between entanglement and Bell locality. The locality of entanglement near the production threshold is further supported by a recent CMS analysis, which reports a significance of more than 5$\textit{σ}$. We also demonstrate that there exists a kinematic region where the spin states of the top-antitop quark are separable, yet they exhibit non-zero discord and magic.

Italy

Marco Fabbrichesi

Roberto Floreanini

Estonia

Luca Marzola

Local vs. nonlocal entanglement in top-quark pairs at the LHC

Generalized uncertainty principles are effective changes to the Heisenberg uncertainty principle that emerge in several quantum gravity models. In the present letter, we study the consequences that two classes of these modifications yield on the physics of neutrinos. Besides analyzing the change in the oscillation probabilities that the generalized uncertainty principles entail, we assess their impact on the neutrino coherence length and their possible interpretation as nonstandard neutrino interactions. Constraints cast by present and planned neutrino experiments on the generalized uncertainty principles parameters are also derived.

Ioannis D. Gialamas

Timo J. Kärkkäinen

Generalized uncertainty principle and neutrino phenomenology

The Belle II collaboration has recently observed the rare decay  $$B^+\rightarrow K^+ \nu \bar{\nu }$$  <math> <mrow> <msup> <mi>B</mi> <mo>+</mo> </msup> <mo>→</mo> <msup> <mi>K</mi> <mo>+</mo> </msup> <mi>ν</mi> <mover> <mrow> <mi>ν</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> </mrow> </math>  , finding an excess with respect to the Standard Model prediction. We explore the possibility that the data entails long-distance interactions induced by a massless dark photon,  $$\gamma _{\scriptscriptstyle {D}}$$  <math> <msub> <mi>γ</mi> <mstyle> <mi>D</mi> </mstyle> </msub> </math>  . This couples at the tree-level to an invisible, dark sector and to the Standard Model via higher-dimensional operators, such as the chromomagnetic-dipole coupling that we use to explain the excess. As the process  $$B^+\rightarrow K^+ \gamma _{\scriptscriptstyle {D}}$$  <math> <mrow> <msup> <mi>B</mi> <mo>+</mo> </msup> <mo>→</mo> <msup> <mi>K</mi> <mo>+</mo> </msup> <msub> <mi>γ</mi> <mstyle> <mi>D</mi> </mstyle> </msub> </mrow> </math>   is forbidden by angular momentum conservation, the transition mediated by the off-shell dark photon yields a three-body final state comprising a pair of dark fermions that show as a missing energy continuum in the detector, faking the neutrino signature. We show that the Belle II data is explained for perturbative values of the parameters of the model. This scenario predicts new contributions to the neutral B meson decays  $$B^0\rightarrow K^* \gamma _{\scriptscriptstyle {D}}$$  <math> <mrow> <msup> <mi>B</mi> <mn>0</mn> </msup> <mo>→</mo> <msup> <mi>K</mi> <mo>∗</mo> </msup> <msub> <mi>γ</mi> <mstyle> <mi>D</mi> </mstyle> </msub> </mrow> </math>  , in which the emission of a on-shell dark photon is allowed, yielding a monochromatic missing energy signature. Analogously, an excess due to the emission of a dark photon is predicted for the  $$B^0_s\rightarrow \phi + E_\textrm{miss}$$  <math> <mrow> <msubsup> <mi>B</mi> <mi>s</mi> <mn>0</mn> </msubsup> <mo>→</mo> <mi>ϕ</mi> <mo>+</mo> <msub> <mi>E</mi> <mtext>miss</mtext> </msub> </mrow> </math>   decay that could be scrutinized next at the LHCb experiments.

Emidio Gabrielli

Kristjan Müürsepp

Martti Raidal

Explaining the  $$B^+\rightarrow K^+ \nu \bar{\nu }$$  <math> <mrow> <msup> <mi>B</mi> <mo>+</mo> </msup> <mo>→</mo> <msup> <mi>K</mi> <mo>+</mo> </msup> <mi>ν</mi> <mover> <mrow> <mi>ν</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> </mrow> </math>   excess via a massless dark photon

A novel first-order action principle has been proposed as the possible foundation for a more fundamental theory of general relativity and the Standard Model. It is shown in this article that the proposal consistently incorporates gravity and matter fields, and guides one to a new and robust path toward unification of fundamental interactions.

Priidik Gallagher

Tomi S. Koivisto

Poland

Ludovic Varrin

Tom Zlosnik

Consistent first-order action functional for gauge theories

We write down the teleparallel equivalent to Hassan–Rosen bigravity, which is written using a torsionful but curvature-free connection. The theories only differ by a boundary term. The equivalence was proven, both by using perturbation theory and Hamiltonian analysis. It is further shown how one can construct novel bigravity theories within the teleparallel framework. Some of those are analyzed through perturbation theory, and it is found that all of the considered novel bigravity theories suffer from pathologies. In particular, it is found that a construction with two copies of new general relativity leads to ghostly degrees of freedom which are not present in the single tetrad teleparallel corresponding theory. We demonstrate how the teleparallel framework allows to easily create theories with derivative interaction. However, it is shown through perturbation theory that the simplest model is not viable. Furthermore, we demonstrate some steps in the Hamiltonian analysis of teleparallel bigravity with two copies of new general relativity and some toy models. The results rule out some of the novel teleparallel bigravity theories, but also demonstrate techniques in perturbation theory and Hamiltonian analysis which could be further used for more profound theories in the future.

Daniel Blixt

Manuel Hohmann

Tomi Koivisto

Teleparallel bigravity

Quantum entanglement of weak interaction gauge bosons produced at colliders can be explored by computing the corresponding polarization density matrix. To this end, we consider the Higgs boson decays  $$H\rightarrow W W^*$$  <math> <mrow> <mi>H</mi> <mo>→</mo> <mi>W</mi> <msup> <mi>W</mi> <mo>∗</mo> </msup> </mrow> </math>   and  $$H\rightarrow Z Z^*$$  <math> <mrow> <mi>H</mi> <mo>→</mo> <mi>Z</mi> <msup> <mi>Z</mi> <mo>∗</mo> </msup> </mrow> </math>  , in which  $$W^*$$  <math> <msup> <mi>W</mi> <mo>∗</mo> </msup> </math>   and  $$Z^*$$  <math> <msup> <mi>Z</mi> <mo>∗</mo> </msup> </math>   are off-shell states, and the WW, WZ and ZZ di-boson production in proton collisions. The polarization density matrix of the di-boson state is determined by the amplitude of the production process and can be experimentally reconstructed from the angular distribution of the momenta of the final states into which the gauge bosons decay. We show that a suitable instance of the Bell inequality is violated in  $$H\rightarrow Z Z^*$$  <math> <mrow> <mi>H</mi> <mo>→</mo> <mi>Z</mi> <msup> <mi>Z</mi> <mo>∗</mo> </msup> </mrow> </math>   to a degree that can be tested at the LHC with future data. The same Bell inequality is violated in the production of WW and ZZ boson pairs for invariant masses above 900 GeV and scattering angles close to  $$\pi /2$$  <math> <mrow> <mi>π</mi> <mo>/</mo> <mn>2</mn> </mrow> </math>   in the center of mass frame. LHC data in this case are not sufficient to establish the violation of the Bell inequality. We also analyze the prospects for detecting Bell inequality violations in di-boson final states at future  $$e^+e^-$$  <math> <mrow> <msup> <mi>e</mi> <mo>+</mo> </msup> <msup> <mi>e</mi> <mo>-</mo> </msup> </mrow> </math>   and muon colliders. A further observable that provides a lower bound on the amount of polarization entanglement in the di-boson system is computed for each of the examined processes. The analytic expressions for the polarization density matrices are presented in full in an Appendix. We also provide the unitary matrices required in the optimization procedure necessary in testing the Bell inequalities.

Bell inequalities and quantum entanglement in weak gauge boson production at the LHC and future colliders

The standard description of particles and fundamental interactions is crucially based on a regular metric background. In the language of differential geometry, this dependence is encoded into the action via Hodge star dualization. As a result, the conventional forms of the scalar and Yang-Mills actions break down in a pregeometric regime where the metric is degenerate. This suggests the use of first order formalism, where the metric may emerge from more fundamental constituents and the theory can be consistently extended to the pregeometric phase. We systematically explore different realizations and interpretations of first order formalism, finding that a fundamental vector or spinor substructure brings about continuum magnetization and polarization as integration constants. This effect is analogous to the description of the cosmological dark sector in a recent self-dual formulation of gravity, and the similar form obtained for the first order Yang-Mills theory suggests new paths toward unification.

Finland

Pregeometric first order Yang-Mills theory

We consider the classically scale invariant Higgs-dilaton model of dynamical symmetry breaking extended with an extra scalar field that plays the role of dark matter. The Higgs boson is light near a critical boundary between different symmetry breaking phases, where quantum corrections beyond the usual Gildener-Weinberg approximation become relevant. This implies a tighter connection between dark matter and Higgs phenomenology. The model has only three free parameters, yet it allows for the observed relic abundance of dark matter while respecting all constraints. The direct detection cross section mediated by the Higgs boson is determined by the dark matter mass alone and is testable at future experiments.

Kristjan Kannike

Niko Koivunen

Aleksei Kubarski

Alessandro Strumia

Venno Vipp

Dark matter-induced multi-phase dynamical symmetry breaking

The recently proposed multiphase criticality principle in Coleman-Weinberg models can provide a new explanation for the hierarchy between the electroweak and new physics scales. When applied to the Standard Model, a Higgs boson as light as the pseudo-Goldstone boson of broken-scale invariance occurs. The suppressed mixing between the two light fields still carries information about the large scale of symmetry breaking, albeit up to logarithmic corrections. In this work we probe this scenario with the present LHC data and assess the impact of future lepton and hadron colliders. Our results show that the multiphase criticality can easily explain the apparent absence of new physics at the energy scales tested in current experiments.

Katri Huitu

India

Subhadeep Mondal

Multiphase critical Higgs boson at colliders

We explore the electroweak vacuum stability in the framework of a recently proposed paradigm for the origin of Yukawa couplings. These arise as low energy effective couplings radiatively generated by portal interactions with a hidden, or dark, sector at the one-loop level. Possible tree-level Yukawa couplings are forbidden by a new underlying symmetry, assumed to be spontaneously broken by the vacuum expectation value of a new scalar field above the electroweak scale. As a consequence, the top Yukawa interaction ceases to behave as a local operator at energies above the new sector scale and, therefore, cannot contribute to the running of the quartic Higgs coupling at higher energies. By studying two complementary scenarios, we explicitly show that the framework can achieve the stability of the electroweak vacuum without particular tuning of parameters. The proposed mechanism requires the existence of a dark sector and new portal messenger scalar interactions that, connecting the Standard Model to the dark sector fields, could be tested at the LHC and future collider experiments.