Search

In this paper, we propose a scotogenic extension of the Standard Model (SM) which can provide a scalar dark matter (DM) candidate in the new, theoretically previously unaddressed, intermediate region (2 0 0 ≤ M DM ≤ 5 5 0 GeV) and also generate light Dirac neutrino masses. In this framework, the SM is extended by three gauge singlet fermions, two singlet scalar fields and one additional scalar doublet along with a continuous global symmetry U (1) B − L and discrete symmetries Z 2 and Z 4 . These additional symmetries prevent the singlet fermions from obtaining Majorana mass terms along with providing the stability to the DM candidate. It is known that in the case of the scalar singlet DM model, the only region which is not yet excluded is a narrow region close to the Higgs resonance m S ≃ m h 2 — others ruled out from different experimental and theoretical bounds. In the case of the inert doublet model, the mass region (∼ 6 0 –80 GeV) and the high-mass region (heavier than 550 GeV) are allowed. This motivates us to explore a parameter range in the intermediate-mass region M W ≤ M DM ≤ 5 5 0 GeV, which we do in a scotogenic extension of SM with a scalar doublet and scalar singlets. The DM in our model is a mixture of singlet and doublet scalars, in the freeze-out scenario. We constrain the allowed parameter space of the model using the Planck bound on present DM relic abundance, neutrino mass and the latest bound on spin-independent DM-nucleon scattering cross-section from the XENON1T experiment. Further, we constrain the DM parameters from the indirect detection bounds arising from the global analysis of the Fermi-LAT observations of dwarf spheroidal satellite (dSphs) galaxies, Higgs invisible decay and Electroweak Precision Test (EWPT) as well. We find that our model findings may provide a viable DM candidate satisfying all the constraints on DM parameters in the new, previously unexplored mass range (2 0 0 ≤ M DM ≤ 5 5 0 GeV). This new window for the DM candidate could be searched in future experiments along with an explanation of the Dirac mass of neutrinos since so far there is no strong evidence in support of the Majorana nature of neutrino mass. [ABSTRACT FROM AUTHOR]

A search for long-lived particles decaying into muon pairs is performed using proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment at the LHC in 2017 and 2018, corresponding to an integrated luminosity of 101 fb−1. The data sets used in this search were collected with a dedicated dimuon trigger stream with low transverse momentum thresholds, recorded at high rate by retaining a reduced amount of information, in order to explore otherwise inaccessible phase space at low dimuon mass and nonzero displacement from the primary interaction vertex. No significant excess of events beyond the standard model expectation is found. Upper limits on branching fractions at 95% confidence level are set on a wide range of mass and lifetime hypotheses in beyond the standard model frameworks with the Higgs boson decaying into a pair of long-lived dark photons, or with a long-lived scalar resonance arising from a decay of a b hadron. The limits are the most stringent to date for substantial regions of the parameter space. These results can be also used to constrain models of displaced dimuons that are not explicitly considered in this paper. [ABSTRACT FROM AUTHOR]

The (g − 2)μ anomaly indicates that the second generation of leptons should have new interactions beyond the standard model. The high flux of νμ and ν ¯ μ at the forward experiments such as FASERν and SND@LHC makes them suitable setups to search for new interactions of the second generation leptons. In this paper, we build a model in which the second generation left-handed leptons couple to a new right-handed neutrino, N and a new Higgs doublet which also couples to the quarks. The scattering of high energy νμ off nuclei can produce N. We investigate how forward experiments can test this model by looking for the N production vertex followed by the displaced vertex of the N decay. Discovering even a single such event can be a harbinger to look for the spectacular signals of the new Higgs doublet production at the LHC. We discuss the possibility of explaining the (g − 2)μ anomaly by adding more generations of N which will lead to chain decays of N and multiple leptons with distinct signals both at forward experiments and at the CMS and ATLAS detectors. Finally, we show that by adding a new light singlet scalar mixed with the neutral component of the new Higgs doublet (i.e., 2HDM+S model), the statistics of the data sample can be dramatically increased. [ABSTRACT FROM AUTHOR]

At the Large Hadron Collider (LHC), both the ATLAS and CMS Collaborations have been searching for light charged Higgs bosons via top (anti)quark production and decays channels, like pp → t t ¯ with one top (anti)quark decaying into a charged Higgs boson and a b (anti)quark, when the decay is kinematically open (i.e., when m H ± ≲ mt). In this paper, we propose new searches at the LHC involving light charged Higgs bosons via their pair production channels like pp → H±h/A and pp → H+H− in the 2-Higgs Doublet Model (2HDM) Type-I and -X scenarios. By focusing on the case where the heavy H state plays the role of the Standard Model (SM)-like Higgs boson with a mass near 125 GeV, we study the aforementioned Higgs boson pair production channels and investigate their bosonic decays, such as H± → W±h and/or H± → W±A. We demonstrate that for a light charged Higgs boson state, with m H ± ≲ mt, at the LHC, such di-Higgs production and decay channels can give rise to signatures with event rates much larger than those emerging from pp → t t ¯ → t b ¯ H− + c.c. We specifically study h/A → b b ¯ and τ+τ− decays. We, therefore, claim that the discussed combination of new production and decay modes can result in an alternative discovery channel for charged Higgs bosons lighter than the top (anti)quark at the LHC within the above two 2HDM Types. Finally, in order to motivate experimentalists in ATLAS and CMS to search for such signatures, we propose 16 Benchmark Points (BPs) which are compatible with both theoretical and experimental constraints. [ABSTRACT FROM AUTHOR]

The Higgs doublet can mediate a long-range interaction between multi-TeV particles coupled to the Weak interactions of the Standard Model, while its emission can lead to very rapid bound-state formation processes and bound-to-bound transitions. Using the rates calculated in a companion paper, here we compute the thermal decoupling of multi-TeV WIMP dark matter coupled to the Higgs, and show that the formation of metastable dark matter bound states via Higgs-doublet emission and their decay decrease the relic density very significantly. This in turn implies that WIMP dark matter may be much heavier than previously anticipated, or conversely that for a given mass, the dark matter couplings to the Higgs may be much lower than previously predicted, thereby altering the dark matter phenomenology. While we focus on a minimal singlet-doublet model in the coannihilation regime, our calculations can be extended to larger multiplets where the effects under consideration are expected to be even more significant. [ABSTRACT FROM AUTHOR]

Although the Higgs potential in the Standard Model (SM) contains only a simple electroweak symmetry breaking vacuum in the small field region, additional metastable or global vacua could exist in models beyond the SM. In this paper, we study one intriguing scenario with an additional electroweak symmetric vacuum that could be the global one. For the thermal universe ending at the current metastable vacuum, the electroweak symmetry should stay non-restored at high temperatures. We realize the scenario in a model with Higgs-portal couplings to SM singlet scalars with approximately global O(N) symmetries with a large N. For a large portion of model parameter space, both the quantum and thermal tunneling rates are suppressed such that our current metastable vacuum is long-lived enough. Our scenario predicts order-one changes for the Higgs self-couplings and a large contribution to the signal of the off-shell Higgs invisible decay. It can be partly probed at the LHC Run 3 and well tested at the high luminosity LHC. We also discuss the subcritical (anti-de Sitter) bubbles from the thermal tunneling that could have a large population and interesting cosmological implications. [ABSTRACT FROM AUTHOR]

A primary goal of present and future colliders is measuring the Higgs couplings to Standard Model (SM) particles. Any observed deviation from the SM predictions for these couplings is a sign of new physics whose energy scale can be bounded from above by requiring tree-level unitarity. In this paper, we extend previous work on unitarity bounds from the Higgs cubic coupling to Higgs couplings to vector bosons and top quarks. We find that HL-LHC measurements of these couplings compatible with current experimental bounds may point to a scale that can be explored at the HL-LHC or a next-generation collider. Our approach is completely model-independent: we assume only that there are no light degrees of freedom below the scale of new physics, and allow arbitrary values for the infinitely many couplings beyond the SM as long as they are in agreement with current measurements. We also extend and clarify the methodology of this analysis, and show that if the scale of new physics is above the TeV scale, then the deviations can be described by the leading higher-dimension gauge invariant operator, as in the SM effective field theory. [ABSTRACT FROM AUTHOR]

The 2HDM possesses a neutral scalar interaction eigenstate whose tree-level properties coincide with the Standard Model (SM) Higgs boson. In light of the LHC Higgs data which suggests that the observed Higgs boson is SM-like, it follows that the mixing of the SM Higgs interaction eigenstate with the other neutral scalar interaction eigenstates of the 2HDM should be suppressed, corresponding to the so-called Higgs alignment limit. The exact Higgs alignment limit can arise naturally due to a global symmetry of the scalar potential. If this symmetry is softly broken, then the Higgs alignment limit becomes approximate (although still potentially consistent with the current LHC Higgs data). In this paper, we obtain the approximate Higgs alignment suggested by the LHC Higgs data as a consequence of a softly broken global symmetry of the Higgs Lagrangian. However, this can only be accomplished if the Yukawa sector of the theory is extended. We propose an extended 2HDM with vector-like top quark partners, where explicit mass terms in the top sector provide the source of the soft symmetry breaking of a generalized CP symmetry. In this way, we can realize approximate Higgs alignment without a significant fine-tuning of the model parameters. We then explore the implications of the current LHC bounds on vector-like top quark partners for the success of our proposed scenario. [ABSTRACT FROM AUTHOR]

In this paper we propose a new reconstruction method to explore the low mass region in the associated production of top-quark pairs (t t ¯ ) with a generic scalar boson (ϕ) at the LHC. The new method of mass reconstruction shows an improved resolution of at least a factor of two in the low mass region when compared to previous methods, without the loss of sensitivity of previous analyses. It turns out that it also leads to an improvement of the mass reconstruction of the 125 GeV Higgs for the same production process. We use an effective Lagrangian to describe a scalar with a generic Yukawa coupling to the top quarks. A full phenomenological analysis was performed, using Standard Model background and signal events generated with MadGraph5_aMC@NLO and reconstructed using a kinematic fit. The use of CP-sensitive variables allows then to maximize the distinction between CP-even and CP-odd components of the Yukawa couplings. Confidence Levels (CLs) for the exclusion of ϕ bosons with mixed CP (both CP-even and CP-odd components) were determined as a function of the top Yukawa couplings to the ϕ boson. The mass range analysed starts slightly above the ϒΥ mass up to 40 GeV, although the analysis can be used for an arbitrary mass. If no new light scalar is found, exclusion limits at 95% CL for the absolute value of the CP-even and CP-odd Yukawa are derived. Finally, we analyse how these limits constrain the parameter space of the complex two-Higgs doublet model (C2HDM). [ABSTRACT FROM AUTHOR]

In this paper, a new technique for reconstructing and identifying hadronically decaying τ+τ− pairs with a large Lorentz boost, referred to as the di-τ tagger, is developed and used for the first time in the ATLAS experiment at the Large Hadron Collider. A benchmark di-τ tagging selection is employed in the search for resonant Higgs boson pair production, where one Higgs boson decays into a boosted b b ¯ pair and the other into a boosted τ+τ− pair, with two hadronically decaying τ-leptons in the final state. Using 139 fb−1 of proton-proton collision data recorded at a centre-of-mass energy of 13 TeV, the efficiency of the di-τ tagger is determined and the background with quark- or gluon-initiated jets misidentified as di-τ objects is estimated. The search for a heavy, narrow, scalar resonance produced via gluon-gluon fusion and decaying into two Higgs bosons is carried out in the mass range 1–3 TeV using the same dataset. No deviations from the Standard Model predictions are observed, and 95% confidence-level exclusion limits are set on this model. [ABSTRACT FROM AUTHOR]

The exotic decay modes of non-Standard Model Higgs bosons are efficient in probing the hierarchical Two Higgs Doublet Models (2HDM). In particular, the decay mode H±→HW± serves as a powerful channel in searching for charged Higgses. In this paper, we analyze the reach for H±→HW±→ t t ¯ W at a 100 TeV pp collider, and show that it extends the reach of the previously studied ττW final states once above the top threshold. Top tagging technique is used, in combination with a boosted decision tree classifier. At the low tan β region, almost the entire hierarchical Type-II 2HDM parameter space can be probed via the combination of all exotic decay channels. [ABSTRACT FROM AUTHOR]

The search for long-lived particles (LLP) is an exciting physics opportunity in the upcoming runs of the Large Hadron Collider. In this paper, we focus on a new search strategy of using the High Granularity Calorimeter (HGCAL), part of the upgrade of the CMS detector, in such searches. In particular, we demonstrate that the high granularity of the calorimeter allows us to see "shower tracks" in the calorimeter, and can play a crucial role in identifying the signal and suppressing the background. We study the potential reach of the HGCAL using a signal model in which the Standard Model Higgs boson decays into a pair of LLPs, h → XX. After carefully estimating the Standard Model QCD and the misreconstructed fake-track backgrounds, we give the projected reach for both an existing vector boson fusion trigger and a novel displaced-track-based trigger. Our results show that the best reach for the Higgs decay branching ratio, BR(h → XX), in the vector boson fusion channel is about O (10−4) with lifetime cτX ∼ 0.1–1 meters, while for the gluon gluon fusion channel it is about O (10−5–10−6) for similar lifetimes. For longer lifetime cτX ∼ 103 meters, our search could probe BR(h → XX) down to a few ×10−4(10−2) in the gluon gluon fusion (vector boson fusion) channels, respectively. In comparison with these previous searches, our new search shows enhanced sensitivity in complementary regions of the LLP parameter space. We also comment on many improvements can be implemented to further improve our proposed search. [ABSTRACT FROM AUTHOR]

This paper presents a study of a possible contribution to a Higgs boson signal in the hh→γγγγ channel due to H→hh decays, in the framework of the CP-conserving 2-Higgs Doublet Model Type-I (2HDM-I), where the heavier of the two CP-even Higgs bosons defined herein, H, is the SM-like Higgs state observed with a mass of 125 GeV at the Large Hadron Collider (LHC). We perform a broad scan of the 2HDM-I parameter space, in presence of both up-to-date theoretical and experimental constraints, in order to extract the interesting regions yielding such a signal. Then, after validating our numerical framework against public experimental analyses carried out at the LHC, we proceed to assess its scope in constraining and/or extracting the gg→H→hh→γγγγ signal in presence of a sophisticated Monte Carlo (MC) simulation. We find that, over a substantial region of the 2HDM-I parameter space presently un-accessible, the LHC will be able to establish such a potential signature in the next 2--3 years. [ABSTRACT FROM AUTHOR]

Beyond the Standard Model (SM) extensions usually include extended Higgs sectors. Models with singlet or doublet fields are the simplest ones that are compatible with the ρ parameter constraint. The discovery of new non-SM Higgs bosons and the identification of the underlying model requires dedicated Higgs properties analyses. In this paper, we compare several Higgs sectors featuring 3 CP-even neutral Higgs bosons that are also motivated by their simplicity and their ability to solve some of the flaws of the SM. They are: the SM extended by a complex singlet field (CxSM), the singlet extension of the 2-Higgs-Doublet Model (N2HDM), and the Next-to-Minimal Supersymmetric SM extension (NMSSM). In addition, we analyse the CP-violating 2-Higgs-Doublet Model (C2HDM), which provides 3 neutral Higgs bosons with a pseudoscalar admixture. This allows us to compare the effects of singlet and pseudoscalar admixtures. Through dedicated scans of the allowed parameter space of the models, we analyse the phenomenologically viable scenarios from the view point of the SM-like Higgs boson and of the signal rates of the non-SM-like Higgs bosons to be found. In particular, we analyse the effect of singlet/pseudoscalar admixture, and the potential to differentiate these models in the near future. This is supported by a study of couplings sums of the Higgs bosons to massive gauge bosons and to fermions, where we identify features that allow us to distinguish the models, in particular when only part of the Higgs spectrum is discovered. Our results can be taken as guidelines for future LHC data analyses, by the ATLAS and CMS experiments, to identify specific benchmark points aimed at revealing the underlying model. [ABSTRACT FROM AUTHOR]

This is the second of a series of papers that explores the physical parameterization, sum rules and unitarity bounds arising from a non-minimal scalar sector of the Standard Model (SM) that consists of N Higgs doublets. In this paper, we focus on the structure and implication of the Yukawa interactions that couple the N scalar doublets to the SM fermions. We employ the charged Higgs basis, which is defined as the basis of scalar fields such that the neutral scalar field vacuum expectation value resides entirely in one of the N scalar doublet fields, and the charged components of the remaining N − 1 scalar doublet fields are the physical (mass-eigenstate) charged Higgs fields. Based on the structure of the Yukawa Lagrangian of the model (and as a consequence of tree-level unitarity), one may deduce numerous sum rules, several of which have not appeared previously in the literature. These sum rules can be used to uncover intimate relations between the structure of the Higgs-fermion couplings and the scalar/gauge couplings. In particular, we show that the approximate alignment limit, in which the W+W− and ZZ couplings to the observed Higgs boson are approximately SM-like, imposes significant constraints on the Higgs-fermion couplings. [ABSTRACT FROM AUTHOR]

In this paper, we study the extended Standard Model (SM) with an extra Higgs doublet and right-handed neutrinos. If the symmetry to distinguish the two Higgs doublets is not assigned, flavor changing neutral currents (FCNCs) involving the scalars are predicted even at the tree level. We investigate the constraints on the FCNCs at the one-loop level, and especially study the semileptonic B meson decays, e.g. B → D(∗)τ ν and B → K(∗)ll processes, where the SM predictions are more than 2σ away from the experimental results. We also consider the flavor-violating couplings involving right-handed neutrinos and discuss if the parameters to explain the excesses of the semileptonic B decays can resolve the discrepancy in the anomalous muon magnetic moment. Based on the analysis, we propose the smoking-gun signals of our model at the LHC. [ABSTRACT FROM AUTHOR]

Most searches for top partners, T, are concerned with top partner pair production. However, as these bounds become increasingly stringent, the LHC energy will saturate and single top partner production will become more important. In this paper we study the novel signature of the top partner produced in association with the SM top, pp→Tt¯+tT¯, in a model where the Standard Model (SM) is extended by a vector-like SU(2)L singlet fermion top partner and a real, SM gauge singlet scalar, S. In this model, pp→Tt¯+tT¯ production is possible through loops mediated by the scalar singlet. We find that, with reasonable coupling strengths, the production rate of this channel can dominate top partner pair production at top partner masses of mT ≳ 1.5 TeV. In addition, this model allows for the exotic decay modes T → tg, T → tγ, and T → tS. In much of the parameter space the loop induced decay T → tg dominates and the top partner is quite long lived. New search strategies are necessary to cover these decay modes. We project the the sensitivity of the high luminosity LHC to pp→Tt¯+tT¯ via a realistic collider study. We find with 3 ab−1, the LHC is sensitive to this process for masses mT ≲ 2 TeV. In addition, we provide appendices detailing the renormalization of this model. [ABSTRACT FROM AUTHOR]

In the near future, fundamental interactions at high-energy scales may be most efficiently studied via precision measurements at low energies. A universal language to assemble and interpret precision measurements is the so-called SMEFT, which is an effective field theory (EFT) where the Standard Model (SM) Lagrangian is extended by higher-dimensional operators. In this paper we investigate the possible impact of the DUNE neutrino experiment on constraining the SMEFT. The unprecedented neutrino flux offers an opportunity to greatly improve the current limits via precision measurements of the trident production and neutrino scattering off electrons and nuclei in the DUNE near detector. We quantify the DUNE sensitivity to dimension-6 operators in the SMEFT Lagrangian, and find that in some cases operators suppressed by an O30 TeV scale can be probed. We also compare the DUNE reach to that of future experiments involving atomic parity violation and polarization asymmetry in electron scattering, which are sensitive to an overlapping set of SMEFT parameters. [ABSTRACT FROM AUTHOR]