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A search for dark matter particles is performed using events with large missing transverse momentum, at least one energetic jet, and no leptons, in proton-proton collisions at $ \\sqrt{s}=13 $ TeV collected with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 12.9 fb$^{−1}$. The search includes events with jets from the hadronic decays of a W or Z boson. The data are found to be in agreement with the predicted background contributions from standard model processes. The results are presented in terms of simplified models in which dark matter particles are produced through interactions involving a vector, axial-vector, scalar, or pseudoscalar mediator. Vector and axial-vector mediator particles with masses up to 1.95 TeV, and scalar and pseudoscalar mediator particles with masses up to 100 and 430 GeV respectively, are excluded at 95% confidence level. The results are also interpreted in terms of the invisible decays of the Higgs boson, yielding an observed (expected) 95% confidence level upper limit of 0.44 (0.56) on the corresponding branching fraction. The results of this search provide the strongest constraints on the dark matter pair production cross section through vector and axial-vector mediators at a particle collider. When compared to the direct detection experiments, the limits obtained from this search provide stronger constraints for dark matter masses less than 5, 9, and 550 GeV, assuming vector, scalar, and axial-vector mediators, respectively. The search yields stronger constraints for dark matter masses less than 200 GeV, assuming a pseudoscalar mediator, when compared to the indirect detection results from Fermi-LAT.

The composition and physical state of dark matter remain among the most pressing unresolved questions in modern physics. Addressing these questions is crucial to our understanding of the Universe’s structure. In this work, we explore the hypothesis that massive scalar bosons, such as axions, constitute the majority of dark matter. We focus on two key aspects of axion physics: (i) the role of axion–neutrino coupling in generating neutrino mass and (ii) the thermodynamic properties of axion dark matter. We propose that the interaction between neutrinos and axions in the early Universe, prior to hadronic formation, could provide a mechanism for finite neutrino masses. Furthermore, to account for the observed large-scale distribution of dark matter, we extend the Bose–Einstein condensation framework and derive the critical temperature Tc that defines the onset of the condensate phase. Our calculations suggest that this temperature ranges from a few 10−3 degrees Kelvin to approximately one Kelvin, depending on the axion scale factor fa. These findings support the plausibility of axions as viable dark matter candidates and emphasize the importance of future experimental searches for axion–neutrino interactions. Additional astrophysical and laboratory investigations could further refine axion mass constraints and shed light on the role of axion condensates in the evolution of the early Universe.

A search for physics beyond the standard model in events with at least three charged leptons (electrons or muons) is presented. The data sample corresponds to an integrated luminosity of 137 fb$^{−1}$ of proton-proton collisions at $ \\sqrt{s} $ = 13 TeV, collected with the CMS detector at the LHC in 2016–2018. The two targeted signal processes are pair production of type-III seesaw heavy fermions and production of a light scalar or pseudoscalar boson in association with a pair of top quarks. The heavy fermions may be manifested as an excess of events with large values of leptonic transverse momenta or missing transverse momentum. The light scalars or pseudoscalars may create a localized excess in the dilepton mass spectra. The results exclude heavy fermions of the type-III seesaw model for masses below 880 GeV at 95% confidence level in the scenario of equal branching fractions to each lepton flavor. This is the most restrictive limit on the flavor-democratic scenario of the type-III seesaw model to date. Assuming a Yukawa coupling of unit strength to top quarks, branching fractions of new scalar (pseudoscalar) bosons to dielectrons or dimuons above 0.004 (0.03) and 0.04 (0.03) are excluded at 95% confidence level for masses in the range 15–75 and 108–340 GeV, respectively. These are the first limits in these channels on an extension of the standard model with scalar or pseudoscalar particles.[graphic not available: see fulltext]

The standard model (SM) production of four top quarks (tt¯tt¯) in proton–proton collisions is studied by the CMS Collaboration. The data sample, collected during the 2016–2018 data taking of the LHC, corresponds to an integrated luminosity of 137fb−1 at a center-of-mass energy of 13TeV. The events are required to contain two same-sign charged leptons (electrons or muons) or at least three leptons, and jets. The observed and expected significances for the tt¯tt¯ signal are respectively 2.6 and 2.7 standard deviations, and the tt¯tt¯ cross section is measured to be 12.6+5.8−5.2fb. The results are used to constrain the Yukawa coupling of the top quark to the Higgs boson, yt, yielding a limit of |yt/ySMt|<1.7 at 95% confidence level, where ySMt is the SM value of yt. They are also used to constrain the oblique parameter of the Higgs boson in an effective field theory framework, H^<0.12. Limits are set on the production of a heavy scalar or pseudoscalar boson in Type-II two-Higgs-doublet and simplified dark matter models, with exclusion limits reaching 350–470GeV and 350–550GeV for scalar and pseudoscalar bosons, respectively. Upper bounds are also set on couplings of the top quark to new light particles.

A search for dark matter is performed looking for events with large missing transverse momentum and a Higgs boson decaying either to a pair of bottom quarks or to a pair of photons. The data from proton-proton collisions at a center-of-mass energy of 13 TeV, collected in 2015 with the CMS detector at the LHC, correspond to an integrated luminosity of 2.3 fb$^{−1}$. Results are interpreted in the context of a Z′-two-Higgs-doublet model, where the gauge symmetry of the standard model is extended by a U(1)$_{Z ′}$ group, with a new massive Z′ gauge boson, and the Higgs sector is extended with four additional Higgs bosons. In this model, a high-mass resonance Z′ decays into a pseudoscalar boson A and a light SM-like scalar Higgs boson, and the A decays to a pair of dark matter particles. No significant excesses are observed over the background prediction. Combining results from the two decay channels yields exclusion limits in the signal cross section in the m$_{Z ′}$ - m$_{A}$ phase space. For example, the observed data exclude the Z$^{′}$ mass range from 600 to 1860 GeV, for Z′ coupling strength g$_{Z ′}$ = 0.8, the coupling of A with dark matter particles g$_{χ}$ = 1, the ratio of the vacuum expectation values tan β = 1, and m$_{A}$ = 300 GeV. The results of this analysis are valid for any dark matter particle mass below 100 GeV.

The method of functional integration has been previously applied to the evaluation of Green functions, in particular to the one-nucleon Green function in the cases of neutral scalar and charged scalar mesons interacting with a static nucleon. This work is extended in this and subsequent papers to pseudoscalar meson theory allowing nucleon recoil. In this paper the formal extension, in particular the inclusion of vacuum polarization effects, is made and the resulting forms discussed. In particular, the comparison between forms arising from the usual interaction of fermions and bosons with the analogous boson-boson forms striking dissimilarity. The reduction of the evaluation of the functional integral is discussed in part II.

Following the formal work of the preceding paper, a method is proposed to evaluate the functional integral which has been derived for the Green function of one nucleon interacting with a pseudoscalar meson field. The method is basically that of stationary phase taken to its second approximation, and since this approximation where applicable is accurate in the limits of strong and weak coupling constants, it is assumed good in general. There are several difficulties involved in the evaluation, and as far as possible these are isolated and discussed with the aid of models each showing one difficulty alone. Combining these separate points, the evaluation of the functional integral is thereby expressed in terms of the solution of a set of coupled equations which provide a basis for a covariant intermediate coupling approach to the problem. The solution of these equations is not attempted in this paper.