LHC Constraints Research Articles

RD(*) and survival of the fittest scalar leptoquark

Motivated by the long-standing discrepancy in lepton flavor universality ratios RD and RD* we assess the status of scalar leptoquark states R2, R˜2 and S1 which can in principle provide a desired enhancement of B(B→D(*)τν) in a minimal setup with two Yukawa couplings only. We consider unavoidable low-energy constraints, Z-pole measurements as well as high-pT constraints. After setting the mass of each leptoquark to 1.5 TeV we find that of all considered states only S1 leptoquark, coupled to both chiralities of leptons and quarks, is still a completely viable solution while the scenario with R2 is in growing tension with Γ(Z→ττ) and with the LHC constraints on the ditau tails at high-pT. We comment on the future experimental tests of the S1 scenario. Published by the American Physical Society 2024

Vector dark matter and LHC constraints, including a 95 GeV light Higgs boson

We study LHC searches for an extension of the Standard Model (SM) by exploiting an additional Abelian UD(1) gauge symmetry and a complex scalar Higgs portal. As the scalar is charged under this gauge symmetry, a vector dark matter (VDM) candidate can satisfy the observed relic abundance and limits from direct dark matter (DM) searches. The ATLAS and CMS experiments have developed a broad search program for the DM candidates, including associate production of Higgs boson, Z boson, and top quark that couple to DM. In this paper, we perform an extensive analysis to constrain the model by using these experiments at LHC. It can be seen that the LHC results can exclude some parts of the parameter space that are still allowed by relic density and the direct detection searches. Using the LHC results, all scalar Higgs portal masses are excluded for the light VDM. Furthermore, exclusion limits on the parameter space of the model by using the new results of the CMS and ATLAS Collaborations for a new light Higgs boson with mass ∼95 GeV are provided. Published by the American Physical Society 2024

Baryogenesis through asymmetric reheating in the mirror twin Higgs

We present the νϕMTH, a Mirror Twin Higgs (MTH) model realizing asymmetric reheating, baryogenesis and twin-baryogenesis through the out-of-equilibrium decay of a right-handed neutrino without any hard \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathbb{Z}}_{2}$$\\end{document} breaking. The MTH is the simplest Neutral Naturalness solution to the little hierarchy problem and predicts the existence of a twin dark sector related to the Standard Model (SM) by a \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathbb{Z}}_{2}$$\\end{document} symmetry that is only softly broken by a higher twin Higgs vacuum expectation value. The asymmetric reheating cools the twin sector compared to the visible one, thus evading cosmological bounds on ∆Neff. The addition of (twin-)colored scalars allows for the generation of the visible baryon asymmetry and, by the virtue of the \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathbb{Z}}_{2}$$\\end{document} symmetry, also results in the generation of a twin baryon asymmetry. We identify a unique scenario with top-philic couplings for the new scalars that can satisfy all cosmological, proton decay and LHC constraints; yield the observed SM baryon asymmetry; and generate a wide range of possible twin baryon DM fractions, from negligible to unity. The viable regime of the theory contains several hints as to the possible structure of the Twin Higgs UV completion. Our results motivate the search for the rich cosmological and astrophysical signatures of twin baryons, and atomic dark matter more generally, at cosmological, galactic and stellar scales.

Walls, bubbles and doom — the cosmology of HEFT

As experiment charts new territory at the electroweak scale, the enterprise to characterise all possible theories becomes all the more necessary. In the absence of new particles, this ambitious enterprise is attainable and has led to the Higgs Effective Field Theory (HEFT) as the most general characterising framework, containing the Standard Model Effective Field Theory (SMEFT) as a subspace. The characterisation of this theory space led to the dichotomy SMEFT vs. HEFT SMEFT as the two possible realisations of symmetry breaking. The criterion to distinguish these two possibilities is non-local in field space, and phenomena which explore field space beyond the neighbourhood of the vacuum manifold are in a singular position to tell them apart. Cosmology allows for such phenomena, and this work focuses on HEFT SMEFT, the less explored of the two options, to find that first order phase transitions with detectable gravitational wave remnants, domain wall formation and vacuum decay in the far, far distant future can take place and single out HEFT SMEFT. Results in cosmology are put against LHC constraints, and the potential of future ground- and space-based experiments to cover parameter space is discussed.

Right-handed slepton bulk regions for dark matter in a generalized minimal supergravity

We study the light right-handed slepton bulk regions for dark matter from the generalized minimal supergravity (GmSUGRA) in the minimal supersymmetric Standard Model. In our comprehensive numerical studies, we show that Rϕ˜≳10% is a conservative criterion to formulate bulk region, where Rϕ˜≡(mϕ˜−mχ˜10)/mχ˜10. For right-handed stau as the next-to-the-lightest supersymmetric particle (NLSP), we find a large viable parameter space, consistent with the current LHC constraints, Planck2018 dark matter relic density bounds, and direct bounds on neutralino-nucleons scattering cross section that naturally supports the right-handed stau bulk regions for dark matter. In particular, the upper bounds on the masses of the lightest supersymmetric particle neutralino and right-handed stau are about 120.4 and 138 GeV, respectively. This bulk region may be beyond the current LHC reach and could be probed at LUX-ZEPLIN, a next-generation dark matter direct-detection experiment, the Future Circular Collider at CERN, and the Circular Electron Positron Collider. However, the scenario with the right-handed selectron as the NLSP is excluded by the LHC supersymmetry searches. Published by the American Physical Society 2024

Global LHC constraints on electroweak-inos with SModelS v2.3

Electroweak-inos, superpartners of the electroweak gauge and Higgs bosons, play a special role in supersymmetric theories. Their intricate mixing into chargino and neutralino mass eigenstates leads to a rich phenomenology, which makes it difficult to derive generic limits from LHC data. In this paper, we present a global analysis of LHC constraints for promptly decaying electroweak-inos in the context of the minimal supersymmetric standard model, exploiting the SMODELS software package. Combining up to 16 ATLAS and CMS searches for which electroweak-ino efficiency maps are available in SMODELS, we study which combinations maximise the sensitivity in different regions of the parameter space, how fluctuations in the data in individual analyses influence the global likelihood, and what is the resulting exclusion power of the combination compared to the analysis-by-analysis approach.

Alternative 3-3-1 models with exotic electric charges

We report the most general classification of 3-3-1 models with β=3 . We found several solutions where anomaly cancellation occurs among fermions of different families. These solutions are particularly interesting as they generate non-universal heavy neutral vector bosons. Non-universality in the standard model fermion charges under an additional gauge group generates charged lepton flavor violation and flavor changing neutral currents; we discuss under what conditions the new models can evade constraints coming from these processes. In addition, we also report the Large Hadron Collider~(LHC) constraints.

B meson anomalies within the triplet vector boson model to the light of recent measurements from LHCb

The triplet vector boson (TVB) is a simplified new physics model involving massive vector bosons transforming as a weak triplet vector. Such a model has been proposed as a combined explanation of the anomalous b→sμ+μ− and b→cτν¯τ data (the so-called B meson anomalies). In this work, we carry out a revamped view of the TVB model by incorporating the most recent 2022 and 2023 LHCb measurements on the lepton-flavor universality ratios R(D(*))=BR(B→D(*)τν¯τ)/BR(B→D(*)ℓ′ν¯ℓ′), R(Λc)=BR(Λb→Λcτν¯τ)/BR(Λb→Λcμν¯μ), and RK(*)=BR(B→K(*)μ+μ−)/BR(B→K(*)e+e−). We perform a global fit to explore the allowed parameter space by the new data and all relevant low-energy flavor observables including the recent experimental progress from Belle, Belle II, and LHCb. Our results are confronted with the recent high-mass dilepton searches at the LHC. We find that for a heavy TVB mass of 1 TeV a common explanation of the B meson anomalies is possible for all data with the recent LHCb measurements on R(D(*)), consistent with LHC constraints. However, this framework is in strong tension with LHC bounds when one considers all data along with the world average values reported by the Heavy Flavor Averaging Group (, Belle, and LHCb) on R(D(*)). Future measurements will be required in order to clarify such a situation. Published by the American Physical Society 2024

Ultraviolet running constraints on low mass dark sectors

We analyze the UV breakdown of Sub-GeV dark matter models that live in a new, dark U(1) sector. Many of these models include a scalar field, which is either the dark matter itself or a dark Higgs field that generates mass terms for the dark matter particle via spontaneous symmetry breaking. A quartic self coupling of this scalar field is generically allowed, and we show that its running is largely governed by the strength of the U(1) gauge field, αD. Furthermore, it consistently has a lower Landau pole than the gauge coupling. Link fields, which couple to both the dark sector and the Standard Model (SM), connect these Landau poles to constraints on SM charged particles. Current LHC constraints on link fields are compatible with αD ≲ 0.5 − 1 for most of the mass range in most models, while smaller values, αD ≲ 0.15, are favored for Majorana DM.

Positivity bounds on Higgs-Portal dark matter

We consider the positivity bounds for WIMP scalar dark matter with effective Higgs-portal couplings up to dimension-8 operators. Taking the superposed states for Standard Model Higgs and scalar dark matter, we show that the part of the parameter space for the effective couplings, otherwise unconstrained by phenomenological bounds, is ruled out by the positivity bounds on the dimension-8 derivative operators. We find that dark matter relic density, direct and indirect detection and LHC constraints are complementary to the positivity bounds in constraining the effective Higgs-portal couplings. In the effective theory obtained from massive graviton or radion, there appears a correlation between dimension-8 operators and other effective Higgs-portal couplings for which the strong constraint from direct detection can be evaded. Nailing down the parameter space mainly by relic density, direct detection and positivity bounds, we find that there are observable cosmic ray signals coming from the dark matter annihilations into a pair of Higgs bosons, WW or ZZ.

Search for leptophilic dark matter at the LHeC

The Large Hadron electron Collider (LHeC) has been designed to push the field of deep inelastic scattering to the high energy and intensity frontier using an intense electron beam with a proton beam from the High Luminosity–Large Hadron Collider. However, LHeC is also a great laboratory for new physics. In this work, we propose a search for dark matter that couples with leptons. This may yield and signals that can be potentially observed through simple missing-energy cuts that suppress the Standard Model background. Considering direct dark matter detection and LHC constraints, we show that LHeC offers a complementary probe for a weak scale dark matter fermion for masses up to 350 GeV, which reproduces the correct relic density, and has interesting implications for lepton flavor violation.

The CMSSM survives Planck, the LHC, LUX-ZEPLIN, Fermi-LAT, H.E.S.S. and IceCube

We revisit the viability of the CMSSM, searching for regions of parameter space that yield a neutralino dark matter density compatible with Planck measurements, as well as LHC constraints including sparticle searches and the mass of the Higgs boson, recent direct limits on spin-independent and -dependent dark matter scattering from the LUX-ZEPLIN (LZ) experiment, the indirect constraints from Fermi-LAT and H.E.S.S. on dark matter annihilations to photons in dwarf spheroidal galaxies and the Galactic Centre, and the IceCube limits on muons from annihilations to neutrinos in the Sun. For representative values of tan beta and A_0 we map in detail the Planck-compatible strips in CMSSM parameter planes, which exhibit multiple distinctive features for large tan beta , A_0 = 0 and mu > 0, and identify portions of the strips that survive all the phenomenological constraints. We find that the most powerful constraint is that from m_h, followed by the LZ limit on spin-independent scattering, whereas sparticle searches at the LHC and indirect dark matter searches are less restrictive. Most of the surviving CMSSM parameter space features a Higgsino-like dark matter particle with a mass sim 1000{-}1100 GeV, which could best be probed with future direct searches for dark matter scattering.

Generic U(1)X models inspired from SO(10)

We propose the family universal $U(1)_X$ models with three right-handed neutrinos by choosing the $U(1)_X$ gauge symmetry as a linear combination of $U(1)_Y\times U(1)_{\chi}$ of $SO(10)$. To be consistent with the quantum gravity effects, we introduced a Dirac fermion $\chi$ as a dark matter candidate, which is odd under the gauged $Z_2$ symmetry after $U(1)_X$ breaking. The isospin violation dark matter with $f_n/f_p = -0.7$ can be realized naturally, and thus the LUX, PANDAX, and XENON1T experimental constraints can be evaded. Moreover, we study the masses and mixings for Higgs and gauge bosons, consider the LHC constraints on the $Z'$ mass, simulate various constraints from dark matter direct and indirect detection experiments, and then present the viable parameter spaces. To study the LHC $Z'$ mass bounds on the generic $U(1)_X$ models, we considered four kinds of scenarios, where scenario II with zero $U(1)_X$ charge for right-handed up-type quarks can relax the LHC $Z'$ mass bound a little bit.

Global constraints on Yukawa operators in the standard model effective theory

CP-violating contributions to Higgs-fermion couplings are absent in the standard model of particle physics (SM), but are motivated by models of electroweak baryogenesis. Here, we employ the framework of the SM effective theory (SMEFT) to parameterise deviations from SM Yukawa couplings. We present the leading contributions of the relevant operators to the fermionic electric dipole moments (EDMs). We obtain constraints on the SMEFT Wilson coefficients from the combination of LHC data and experimental bounds on the electron, neutron, and mercury EDMs. We perform, for the first time, a combined fit to LHC and EDM data allowing the presence of CP-violating contributions from several fermion species simultaneously. Among other results, we find non-trivial correlations between EDM and LHC constraints even in the multi-parameter scans, for instance, when floating the CP-even and CP-odd couplings to all third-generation fermions.

Supersymmetric explanation of the muon g – 2 anomaly with and without stable neutralino

In this paper we explore the possibility of explaining the muon g − 2 anomaly in various types of supersymmetric extensions of the Standard Model. In particular, we investigate and compare the phenomenological constraints in the MSSM with stable neutralino and the other types of scenarios where the neutralino is unstable. For the latter case we study the Gauge Mediated SUSY Breaking (GMSB) scenario with very light gravitino and the UDD-type R-Parity Violating (RPV) scenario. In the MSSM with stable neutralino, the parameter region favoured by the (g − 2)μ is strongly constrained by the neutralino relic abundance and the dark matter direct detection experiments, as well as by the LHC searches in the lepton plus missing transverse energy channel. On the other hand, the scenarios without stable neutralino are free from the dark matter constraints, while the LHC constraints depends strongly on the decay of the neutralino. We find that in GMSB the entire parameter region favoured by the muon g − 2 is already excluded if the Next Lightest SUSY Particle (NLSP) is the neutralino. In the GMSB scenario with a stau NSLP and in the RPV scenario, LHC constraints are weaker than the stable neutralino case and a larger region of parameter space is available to fit the (g − 2)μ anomaly.

Z′-mediated Majorana dark matter: suppressed direct-detection rate and complementarity of LHC searches

We study the direct-detection rate for axial-vectorial dark matter scattering off nuclei in an SU(2) × U(1) invariant effective theory and compare it against the LHC reach. Current constraints from direct detection experiments are already bounding the mediator mass to be well into the TeV range for WIMP-like scenarios. This motivates a consistent and systematic exploration of the parameter space to map out possible regions where the rates could be suppressed. We do indeed find such regions and proceed to construct consistent UV models that generate the relevant effective theory. We then discuss the corresponding constraints from both collider and direct-detection experiments on the same parameter space. We find a benchmark scenario, where even for future XENONnT experiment, LHC constraints will have a greater sensitivity to the mediator mass.

Constraining the {mathcal {C}}{mathcal {P}} structure of Higgs-fermion couplings with a global LHC fit, the electron EDM and baryogenesis

{mathcal {C}}{mathcal {P}} violation in the Higgs couplings to fermions is an intriguing, but not yet extensively explored possibility. We use inclusive and differential LHC Higgs boson measurements to fit the {mathcal {C}}{mathcal {P}} structure of the Higgs Yukawa couplings. Starting with simple effective models featuring {mathcal {C}}{mathcal {P}} violation in a single Higgs–fermion coupling, we probe well-motivated models with up to nine free parameters. We also investigate the complementarity of LHC constraints with the electron electric dipole moment bound, taking into account the possibility of a modified electron Yukawa coupling, and assess to which extent {mathcal {C}}{mathcal {P}} violation in the Higgs–fermion couplings can contribute to the observed baryon asymmetry of the universe. Even after including the recent analysis of angular correlations in Hrightarrow tau ^+tau ^- decays, we find that a complex tau Yukawa coupling alone may be able to account for the observed baryon asymmetry, but with large uncertainties in the baryogenesis calculation. A combination of complex top and bottom quark Yukawa couplings yields a result four times larger than the sum of their separate contributions, but remains insufficient to account for the observed baryon asymmetry.

Gravitational waves in models with multicritical-point principle

The multicritical-point principle (MPP) provides a natural explanation of the large hierarchy between the Planck and electroweak scales. We consider a scenario in which MPP is applied to the Standard Model extended by two real singlet scalar fields phi and S, and a dimensional transmutation occurs by the vacuum expectation value of phi . In this paper, we focus on the critical points that possess a {mathbb {Z}}_2 symmetry Srightarrow -S and all the other fields are left invariant. Then S becomes a natural dark matter (DM) candidate. Further, we concentrate on the critical points where phi does not possess further {mathbb {Z}}_2 symmetry so that there is no cosmological domain-wall problem. Among such critical points, we focus on maximally critical one called CP-1234 that fix all the superrenormalizable parameters. We show that there remains a parameter region that satisfies the DM relic abundance, DM direct-detection bound and the current LHC constraints. In this region, we find a first-order phase transition in the early universe around the TeV-scale temperature. The resultant gravitational waves are predicted with a peak amplitude of {{mathcal {O}}}(10^{-12}) at a frequency of 10^{-2}{-}10^{-1} Hz, which can be tested with future space-based instruments such as DECIGO and BBO.

Addendum to “Leptophilic U(1) massive vector bosons from large extra dimensions: Reexamination of constraints from LEP data” [Phys. Lett. B 820 (2021) 136585

Very recently, we proposed an explanation of the discrepancy between the measured anomalous magnetic moment of the muon and the Standard Model (SM) prediction in which the dominant contribution to (g−2)μ originates in Kaluza-Klein (KK) excitations (of the lepton gauge boson) which do not mix with quarks (to lowest order) and therefore can be quite light avoiding LHC constraints. In this addendum we reexamine the bounds on 4-fermion contact interactions from precise electroweak measurements and show that the constraints on KK masses and couplings are more severe than earlier thought. However, we demonstrate that our explanation remains plausible if a few KK modes are lighter than LEP energy, because if this were the case the contribution to the 4-fermion scattering from the internal propagator would be dominated by the energy and not by the mass. To accommodate the (g−2)μ discrepancy we assume that the lepton number L does not partake in the hypercharge and propagates in one extra dimension (transverse to the SM branes): for a mass of the lowest KK excitation of 60 GeV (lower than the LEP energy), the string scale is roughly 10 TeV while the L gauge coupling is of order ∼10−1.

Can electron and muon g-2 anomalies be jointly explained in SUSY?

The FNAL+BNL measurements for muon g-2 is 4.2sigma above the SM prediction, and the Berkeley ^{133}Cs measurement for the fine-structure constant alpha _mathrm{em} leads to the SM prediction for electron g-2 which is 2.4sigma above the experimental value. Hence, a joint explanation of both anomalies requires a positive contribution to muon g-2 and a negative contribution to electron g-2, which is rather challenging. In this work we explore the possibility of such a joint explanation in the minimal supersymmetric standard model (MSSM). Assuming no universality between smuon and selectron soft masses, we find out a part of parameter space for a joint explanation at 2sigma level, i.e., mu M_1,mu M_2<0, m_{L1}, m_{E2}<200 GeV, m_{L2} being much larger than the soft masses of other sleptons, |M_1|<125 GeV and mu <400 GeV. This part of parameter space can survive LHC and LEP constraints, but gives an over-abundance for dark matter if the bino-like lightest neutralino is assumed to be the dark matter candidate. With the assumption that the dark matter candidate is a superWIMP (say a pseudo-goldstino in multi-sector SUSY breaking scenarios, whose mass can be as light as GeV and produced from the late-decay of the thermally freeze-out lightest neutralino), the dark matter problem can be avoided. So, we conclude that the MSSM may give a joint explanation for the muon and electron g-2 anomalies at 2sigma level (the muon g-2 anomaly can be even ameliorated to 1sigma ).