<p>This paper studies the dynamics of scalar particle production, focusing on the presence of multiple fields and couplings in the medium. The interplay of various fields and couplings can influence the production rate, potentially overshadowing the effect of electrons alone. The plasma mixing, which induces the resonance and screening of scalar processes, is shown to be modified by the in-medium effects depending on the type of processes and field contents. Incorporating these in-medium effects into the analysis of stellar cooling via scalar emission allows for the emergence of various features of multifield effects given in several types of scalar models.</p>

Taiwan

Yasuhiro Yamamoto

Japan

Koichi Yoshioka

Multifield effects on scalar production in stars

We revisit the stellar cooling limits on the light scalar boson whose coupling to the Standard Model particles is described by its mixing with the Higgs boson. Strong constraints have been obtained from the electron-nucleus bremsstrahlung process (<math><mi>N</mi><mi>e</mi><mo>→</mo><mi>N</mi><mi>e</mi><mi>S</mi></math>) and the resonant plasma effect in the medium. We find that the bremsstrahlung contribution from the electron and nucleus scattering is of similar magnitude to the plasma mixing effect including the off-resonant mixing. The constraints on the scalar coupling are found to be about three orders of magnitude weaker than the previous evaluations because of the missing factor of the electron-nucleon mass ratio. For white dwarfs, the stellar cooling constraint is even more suppressed due to the Pauli blocking effect. We obtain limits on the Higgs-scalar mixing angle of <math><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>10</mn></mrow></msup></math>–<math><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>9</mn></mrow></msup></math>, which are given by white dwarfs or red giants up to the luminosity limits, in the region where the scalar mass is lighter than about 10 keV.

Stellar cooling limits on light scalar boson revisited

We introduce a new linear relation in the isotope shifts of atomic spectroscopy. While the famous King relation is the linear relation among the different transitions, the new one is the linear relation among the different isotope pairs. Since we obtain this relation by exchanging the roles of the electronic and the nuclear factors in the original relation, we call it the dual King relation. This relation shows us similar information to the original King relation without including new fit parameters when we measure the isotope shifts of many transitions. In the dual King relation, the fit coefficients consist of the nuclear factors. Then, the fit results give us constraints to the ratios of the isotope dependence independent of the electron wave functions. This helps us to test the origin of unknown higher order isotope shifts. We show that the dual King relation can also be employed to constrain the weakly interacting light new boson at the same level as the original King relation.

The dual King relation

We use the framework of asymptotically safe quantum gravity to derive predictions for scalar leptoquark solutions to the  $$b\rightarrow s$$  <math> <mrow> <mi>b</mi> <mo>→</mo> <mi>s</mi> </mrow> </math>   and  $$b\rightarrow c$$  <math> <mrow> <mi>b</mi> <mo>→</mo> <mi>c</mi> </mrow> </math>   flavor anomalies. The presence of an interactive UV fixed point in the system of gauge and Yukawa couplings imposes a set of boundary conditions at the Planck scale, which allows one to determine low-energy values of the leptoquark Yukawa matrix elements. As a consequence, the allowed leptoquark mass range can be significantly narrowed down. We find that a consistent gravity-driven solution to the  $$b\rightarrow s$$  <math> <mrow> <mi>b</mi> <mo>→</mo> <mi>s</mi> </mrow> </math>   anomalies predicts a leptoquark with the mass of 4–7  $$\,\mathrm {TeV}$$  <math> <mrow> <mspace width="0.166667em"></mspace> <mi>TeV</mi> </mrow> </math>  , entirely within the reach of a future hadron-hadron collider with  $$\sqrt{s}=100\,\mathrm {TeV}$$  <math> <mrow> <msqrt> <mi>s</mi> </msqrt> <mo>=</mo> <mn>100</mn> <mspace width="0.166667em"></mspace> <mi>TeV</mi> </mrow> </math>  . Conversely, in the case of the  $$b\rightarrow c$$  <math> <mrow> <mi>b</mi> <mo>→</mo> <mi>c</mi> </mrow> </math>   anomalies the asymptotically safe gravity framework predicts a leptoquark mass at the edge of the current LHC bounds. Complementary signatures appear in flavor observables, namely the (semi)leptonic decays of B and D mesons and kaons.

Poland

Kamila Kowalska

Enrico Sessolo

Flavor anomalies from asymptotically safe gravity

Abstract Isotope shift of atomic spectra is considered as a probe of new interaction between electrons and neutrons in atoms. We employ the method of seeking a breakdown of King’s linearity in the isotope shifts of two atomic transitions. In the present work, we evaluate the magnitudes of the nonlinearity using relativistic wave functions and the result is compared with that of nonrelativistic wave functions from our previous work. It turns out that the nonrelativistic calculation underestimates the nonlinearity owing to the new interaction in the mass range of the mediator greater than 1 MeV. Further, we find that the nonlinearity within the standard model of particle physics is significantly magnified by the relativistic effect in the  state. To get rid of this obstacle in the new physics search, we suggest avoiding  and that e.g.  should be used instead.

Minoru Tanaka

Relativistic effects in the search for new intra-atomic force with isotope shifts

We derive constraints from flavor and LHC searches on charmphilic contributions to the muon anomalous magnetic moment with a single leptoquark. Only the scalar leptoquarks <math><msub><mi>S</mi><mn>1</mn></msub></math> and <math><msub><mi>R</mi><mn>2</mn></msub></math> are relevant for the present analysis. We find that for <math><msub><mi>S</mi><mn>1</mn></msub></math> some parameter space remains consistent at <math><mn>2</mn><mi>σ</mi></math> with the Brookhaven National Laboratory measurement of <math><mo>(</mo><mi>g</mi><mo>−</mo><mn>2</mn><msub><mo>)</mo><mi>μ</mi></msub></math>, under the assumption that the left-type coupling between the muon and the charm quark is a free parameter. The surviving parameter space is, on the other hand, going to be probed in its entirety at the LHC with <math><mn>300</mn><mtext> </mtext><mtext> </mtext><msup><mi>fb</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math> of luminosity or less. All other possibilities are excluded by the LHC dimuon search results in combination with several flavor bounds, which together require one to introduce sizable couplings to the top quark to be evaded.

Enrico Maria Sessolo

Constraints on charmphilic solutions to the muon <math><mi>g</mi><mo>−</mo><mn>2</mn></math> with leptoquarks

In the development of atomic clocks, some atomic transition frequencies are measured with remarkable precision. These measured spectra may include the effects of a new force mediated by a weakly interacting boson. Such effects might be distilled out from possible violation of a linear relation in isotope shifts between two transitions, as known as King’s linearity, with relatively suppressed theoretical uncertainties. We discuss the experimental sensitivity to a new force in the test of the linearity as well as the linearity violation owing to higher-order effects within the Standard Model. The sensitivity to new physics is limited by such effects. We have found that, for Yb+ , the higher-order effect is in the reach of future experiments. The sensitivity to a heavy mediator is also discussed. It is analytically clarified that the sensitivity becomes weaker than that in the literature. Our numerical results of the sensitivity are compared with other weak force search experiments.

Kyoko Mikami

South Korea

Probing new intra-atomic force with isotope shifts

We study a class of models in which the Higgs pair production is enhanced at hadron colliders by an extra neutral scalar. The scalar particle is produced by the gluon fusion via a loop of new colored particles, and decays into di-Higgs through its mixing with the Standard Model Higgs. Such a colored particle can be the top/bottom partner, such as in the dilaton model, or a colored scalar which can be triplet, sextet, octet, etc., called leptoquark, diquark, coloron, etc., respectively. We examine the experimental constraints from the latest Large Hadron Collider (LHC) data, and discuss the future prospects of the LHC and the Future Circular Collider up to 100Â TeV. We also point out that the 2.4Ï excess in the bbÂ¯Î³Î³ final state reported by the ATLAS experiment can be interpreted as the resonance of the neutral scalar at 300Â GeV.

Koji Nakamura

Kenji Nishiwaki

Kin-ya Oda

Seong Chan Park

Di-Higgs enhancement by neutral scalar as probe of new colored sector

We study the Higgs derivative interactions on models including arbitrary number of the Higgs doublets. These interactions are generated by two ways. One is higher order corrections of composite Higgs models, and the other is integration of heavy scalars and vectors. In the latter case, three point couplings between the Higgs doublets and these heavy states are the sources of the derivative interactions. Their representations are constrained to couple with the doublets. We explicitly calculate all derivative interactions generated by integrating out. Their degrees of freedom and conditions to impose the custodial symmetry are discussed. We also study the vector boson scattering processes with a couple of two Higgs doublet models to see experimental signals of the derivative interactions. They are differently affected by each heavy field.

Yohei Kikuta

Spain

Derivative interactions and perturbative UV contributions in N Higgs doublet models

Leptophilic interactions can only be observed at the LHC in four-lepton final states. If these interactions are mediated by a resonance in the di-leptonic channel with renormalizable couplings, the mediator must have spin 1. We study the LHC reach for such a vector boson allowing for arbitrary couplings. We find that only couplings to muons can be probed at the LHC because lepton flavor violating couplings are constrained by rare processes, couplings to electrons by LEP and the LHC is not sensitive to final states involving taus in this case. The ILC becomes then complementary to the LHC as it will provide the best limits on Z ′ couplings to tau leptons. A prominent example is the case of the anomaly-free Z ′ coupling to the muon minus tau lepton number L μ − L τ . If no departure from the Standard Model is observed at the LHC, the most stringent bounds on this vector boson are provided from events with only three charged leptons plus missing energy. Masses of the order of 1 TeV can be probed at the high-luminosity phase of the LHC for Z ′ couplings of order one. Generic four-lepton operators parametrizing leptophilic interactions can be also constrained using three and four (or two at the ILC) charged-lepton samples, but the corresponding limits are marginal, if meaningful, because the resonant behavior appears to be essential for the signal to be significant.