We study Higgs boson production at <math><msup><mi>μ</mi><mo>+</mo></msup><msup><mi>μ</mi><mo>+</mo></msup></math> colliders at high energy. Since both initial-state particles are positively charged, there is no <math><mi>W</mi></math> boson fusion at the leading order, as it requires a <math><msup><mi>W</mi><mo>+</mo></msup><msup><mi>W</mi><mo>−</mo></msup></math> pair. However, we find that the cross section of the higher-order, <math><mi>γ</mi></math>-and <math><mi>Z</mi></math>-mediated <math><mi>W</mi></math> boson fusion process is large at high center-of-mass energies <math><msqrt><mi>s</mi></msqrt></math>, growing as <math><mo>(</mo><mi>log</mi><mi>s</mi><msup><mo>)</mo><mn>3</mn></msup></math>. This is in contrast to the <math><mi>log</mi><mi>s</mi></math> behavior of the leading-order <math><mi>W</mi></math> boson fusion. Thus, even though it is a higher-order process, the rate of Higgs boson production for 10 TeV energies at <math><msup><mi>μ</mi><mo>+</mo></msup><msup><mi>μ</mi><mo>+</mo></msup></math> colliders with polarized beams can be as high as about half of the one at <math><msup><mi>μ</mi><mo>+</mo></msup><msup><mi>μ</mi><mo>−</mo></msup></math> colliders, assuming the same integrated luminosity. To calculate the cross section of this process accurately, we carefully treat the collinear emission of the photon in the intermediate state. The thereby obtained large cross section furthermore shows the significance of Higgs production with an extra <math><mi>W</mi></math> boson in the final state also at <math><msup><mi>μ</mi><mo>+</mo></msup><msup><mi>μ</mi><mo>−</mo></msup></math> and <math><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> colliders.

Germany

Japan

Yu Hamada

Ryuichiro Kitano

Ryutaro Matsudo

Shohei Okawa

Ryoto Takai

Hiromasa Takaura

Lukas Treuer

Higgs boson production at <math><mrow><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup></mrow></math> colliders

Models based on a   <math> <mi>U</mi> <msub> <mfenced> <mn>1</mn> </mfenced> <mrow> <msub> <mi>L</mi> <mi>μ</mi> </msub> <mo>−</mo> <msub> <mi>L</mi> <mi>τ</mi> </msub> </mrow> </msub> </math>  $$ \textrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$  gauge symmetry can explain the discrepancy between the measured value and theoretical prediction of the muon anomalous magnetic moment. Based on the latest experimental results, we revisit the analysis of neutrino mass matrix structures in minimal   <math> <mi>U</mi> <msub> <mfenced> <mn>1</mn> </mfenced> <mrow> <msub> <mi>L</mi> <mi>μ</mi> </msub> <mo>−</mo> <msub> <mi>L</mi> <mi>τ</mi> </msub> </mrow> </msub> </math>  $$ \textrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$  models where the   <math> <mi>U</mi> <msub> <mfenced> <mn>1</mn> </mfenced> <mrow> <msub> <mi>L</mi> <mi>μ</mi> </msub> <mo>−</mo> <msub> <mi>L</mi> <mi>τ</mi> </msub> </mrow> </msub> </math>  $$ \textrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$  symmetry breaking is caused by a single scalar field. Due to the charge assignment of the scalar field, each model predicts a unique structure of the neutrino mass matrix, which demands non-trivial relations among neutrino mass and mixing parameters. We find that the model called type 2 +1, which features an SU(2) L  doublet scalar Φ+1 with the   <math> <mi>U</mi> <msub> <mfenced> <mn>1</mn> </mfenced> <mrow> <msub> <mi>L</mi> <mi>μ</mi> </msub> <mo>−</mo> <msub> <mi>L</mi> <mi>τ</mi> </msub> </mrow> </msub> </math>  $$ \textrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$  charge +1 and the hypercharge +1/2 and predicts the B  3  texture structure, is marginally acceptable under the current neutrino oscillation data and cosmological observation. When the   <math> <mi>U</mi> <msub> <mfenced> <mn>1</mn> </mfenced> <mrow> <msub> <mi>L</mi> <mi>μ</mi> </msub> <mo>−</mo> <msub> <mi>L</mi> <mi>τ</mi> </msub> </mrow> </msub> </math>  $$ \textrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$  gauge symmetry is broken by the vacuum expectation value of the standard model non-singlet representation such as Φ+1, there are additional contributions to flavor-changing meson decay processes and atomic parity violation via mixing between the Z boson and the   <math> <mi>U</mi> <msub> <mfenced> <mn>1</mn> </mfenced> <mrow> <msub> <mi>L</mi> <mi>μ</mi> </msub> <mo>−</mo> <msub> <mi>L</mi> <mi>τ</mi> </msub> </mrow> </msub> </math>  $$ \textrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$  gauge boson Z  ′ . We newly evaluate the model-dependent constraints on the model and find that the type 2 +1 model is robustly ruled out. The model is extended to have an additional vacuum expectation value of a standard model singlet scalar in order to avoid the stringent constraints via the Z – Z  ′  mixing. Finally, we clarify the allowed range of the ratio of these vacuum expectation values.

Kento Asai

Coh Miyao

Spain

Koji Tsumura

New constraints on gauged   <math> <mi>U</mi> <msub> <mfenced> <mn>1</mn> </mfenced> <mrow> <msub> <mi>L</mi> <mi>μ</mi> </msub> <mo>−</mo> <msub> <mi>L</mi> <mi>τ</mi> </msub> </mrow> </msub> </math>  $$ \textrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$  models via Z − Z  ′  mixing

Minimal Flavor Violation (MFV) offers an appealing framework for exploring physics beyond the Standard Model. Interestingly, within the MFV framework, a new colorless field that transforms non-trivially under a global SU(3) quark flavor group can naturally be stable. Such a new field is thus a promising dark matter candidate, provided it is electrically neutral. We extend the MFV framework for dark matter and demonstrate that dark matter can naturally be multi-component across a broad parameter space. For illustration, we consider a gauge singlet, flavor triplet scalar field and identify parameter spaces for multi-component dark matter, where only the lightest flavor component is absolutely stable and heavy flavor components are decaying with lifetimes sufficiently longer than the age of the universe. Phenomenological, cosmological and astrophysical aspects of multi-component flavored dark matter are briefly discussed.

Italy

Federico Mescia

Keyun Wu

Multi-component dark matter from Minimal Flavor Violation

We study phenomenology of a light scalar dark matter (DM). In the model, there is an inert doublet scalar and a singlet Dirac fermion <math><mi>ψ</mi></math>, both charged under a global <math><msub><mi>Z</mi><mn>2</mn></msub></math> symmetry. The mass of the lightest inert scalar <math><mi>H</mi></math> can be lighter than 10 GeV by imposing appropriate relations between three scalar quartic couplings. The lightest <math><msub><mi>Z</mi><mn>2</mn></msub></math> odd particle is stable and DM. In this paper, focusing on the parameter space where <math><mi>H</mi></math> is lighter than <math><mi>ψ</mi></math> and is DM, we discuss DM physics related to relic density, direct detection, indirect detection, collider searches, and other cosmological observations. We clarify differences from the case where <math><mrow><mi>ψ</mi></mrow></math> is instead DM, which has been focused on in previous works.

Ryo Higuchi

Syuhei Iguro

Yuji Omura

Light mass window of inert doublet dark matter with lepton portal interaction

Upcoming neutrino telescopes promise a new window onto the interactions of neutrinos with matter at ultrahigh energies (E  ν  = 107–1010 GeV), and the possibility to detect deviations from the Standard Model predictions. In this paper, we update previous predictions for the enhancement of the neutrino-nucleon cross-section for motivated leptoquark models and show the latest neutrino physics bound, as well as analyse the latest LHC pair production and Drell-Yan data, and flavour constraints (some of which were previously missed). We find that, despite the next generation of neutrino experiments probing the highest energies, they will not be enough to be competitive with collider searches.

Matthew Kirk

A ν window onto leptoquarks?

We study the impact of renormalization group effects on QCD axion phenomenology. Focusing on the Dine-Fischler-Srednicki-Zhitnitsky model, we argue that the relevance of running effects for the axion couplings crucially depends on the scale where the heavier Higgs scalars are integrated out. We study the impact of these effects on astrophysical and cosmological bounds as well as on the sensitivity of helioscopes experiments such as IAXO and XENONnT, showing that they can be sizable even in the most conservative case in which the two Higgs doublets remain as light as the TeV scale. We provide simple analytical expressions that accurately fit the numerical solutions of the renormalization group equations as a function of the mass scale of the heavy scalars.

Luca Di Luzio

United States

Maurizio Giannotti

Estonia

Enrico Nardi

Switzerland

France

Gioacchino Piazza

Running effects on QCD axion phenomenology

We examine the sensitivity of the Large Hadron Collider (LHC) to light lepton portal dark matter with its mass below 10 GeV. The model features an extra doublet scalar field and singlet Dirac dark matter, which have Yukawa interactions with left-handed leptons. To correctly produce the dark matter abundance via the thermal freeze-out, a large mass splitting among the extra scalars is required, thus providing a light neutral scalar below   <math> <mi>O</mi> <mfenced> <mn>10</mn> </mfenced> <mi>GeV</mi> </math>  $$ \mathcal{O}(10)\textrm{GeV} $$  and heavy neutral and charged scalars at the electroweak scale. In this paper, we focus on the electroweak pair-production of the extra scalars with subsequent model-specific scalar decays and evaluate the current constraints with the LHC Run 2 data and the discovery potential at the High Luminosity LHC (HL-LHC). It turns out that a large part of the theoretically allowed parameter space can be tested at the HL-LHC by taking into account complementarity between slepton searches and mono-Z plus missing transverse energy search. We also discuss same-sign charged scalar production as a unique prediction of the model, and the implication of the collider searches in the thermal dark matter scenario.

Light lepton portal dark matter meets the LHC

It has been recently pointed out that in certain axion models it is possible to suppress simultaneously both the axion couplings to nucleons and electrons, realizing the so-called astrophobic axion scenarios, wherein the tight bounds from SN1987A and from stellar evolution of red giants and white dwarfs are greatly relaxed. So far, however, the conditions for realizing astrophobia have only been set out in tree-level analyses. Here we study whether these conditions can still be consistently implemented once renormalization group effects are included in the running of axion couplings. We find that axion astrophobia keeps holding, albeit within fairly different parameter space regions, and we provide analytical insights into this result. Given that astrophobic axion models generally feature flavor-violating axion couplings, we also assess the impact of renormalization group effects on axion-mediated flavor-violating observables.

Renormalization group effects in astrophobic axion models

We study a renormalizable scalar singlet dark matter model based on <math><msub><mi>Z</mi><mn>4</mn></msub></math> lepton flavor symmetry. A <math><mrow><mi>μ</mi><mi>τ</mi></mrow></math>-philic scalar doublet is introduced as a mediator which connects dark matter and standard model particles. The observed relic abundance of the dark matter is easily maintained while satisfying the current severe constraints on the dark matter from various experiments and observations thanks to the flavor off-diagonal interactions of scalar mediators. We further explore the possibility of dark matter direct detection through the one-loop process. We also find that the relic abundance of the dark matter and the discrepancy of the muon anomalous magnetic moment can be explained by the <math><mrow><mi>μ</mi><mi>τ</mi></mrow></math>-philic scalar mediator simultaneously.

Scalar dark matter with a <math><mi>μ</mi><mi>τ</mi></math> flavored mediator

We study a lepton portal dark matter model, motivated by the deviation of the <math><mi>W</mi></math> boson mass reported by the CDF collaboration. We introduce vectorlike leptons and a scalar dark matter (DM) that exclusively couples to the extra leptons and muon. The one-loop corrections induced by the new particles can shift the <math><mi>W</mi></math> boson mass. Besides, the discrepancy in the muon anomalous magnetic moment and the DM density can simultaneously be explained by this setup, if the vectorlike lepton is lighter than 200 GeV and nearly degenerate with the DM particle. We also see that the constraints on such a light extra lepton from the collider experiments can be evaded due to the existence of the DM particle.

South Korea

Junichiro Kawamura

<math><mi>W</mi></math> boson mass and muon <math><mi>g</mi><mo>−</mo><mn>2</mn></math> in a lepton portal dark matter model