We express the oblique parameters $S$, $T$, $U$, $V$, $W$, and $X$ in terms of the corresponding mixing matrices in the framework of three BSM models with three CP-even neutral scalars. We consider three types of the extension of the scalar sector of the SM with non-standard (i) two real singlet scalars, (ii) one complex doublet and one real singlet scalar, and (iii) two complex doublets. We present the expressions such that one can use these when all the neutral CP-even scalars have VEV, or one of them does not have any VEV. The principal benifit of presenting the oblique parameters in this way is, the sole knowledge of the mixing matrices in the corresponding scalar sector is enough to extract the expression of the oblique parameter of that particular BSM model. This paper also presents some plots, for reference, showing the allowed region of the masses of the three CP-even neutral scalars and the three mixing angles of the three above-mentioned models.
We consider an effective field theory framework with three standard model (SM) gauge singlet right handed neutrinos, and an additional SM gauge singlet scalar field. The framework successfully generates eV masses of the light neutrinos via seesaw mechanism, and accommodates a feebly interacting massive particle (FIMP) as dark matter candidate. Two of the gauge singlet neutrinos participate in neutrino mass generation, while the third gauge singlet neutrino is a FIMP dark matter. We explore the correlation between the $\textit{vev}$ of the gauge singlet scalar field which translates as mass of …
In scenarios beyond the Standard Model (BSM) characterized by charged ($W^\prime$) or neutral ($Z^\prime$) massive gauge bosons with large width, resonant mass searches are not very effective, so that one has to exploit the tails of the mass distributions measured at the Large Hadron Collider (LHC). In this case, the LHC sensitivity to new physics signals is influenced significantly by systematic uncertainties associated with the Parton Distribution Functions (PDF), particularly in the valence quark sector relevant for the multi-TeV mass region. As a BSM framework featuring such conditions, we…
Experiments searching for Heavy Neutral Leptons (HNLs) typically interpret their results within simplified models consisting of a single HNL coupled to a single lepton flavor. However, any model which aims to describe neutrino oscillations necessarily features more than one HNL, coupled to several flavors. As we show in this work, the reinterpretation of the results of experimental searches in terms of realistic models is a non-trivial task. We perform a detailed reinterpretation of the latest ATLAS search for prompt HNLs in W decays within a minimal low-scale seesaw with two HNLs. We show tha…
Additional Higgs bosons appear in many extensions of the Standard Model (SM). While most existing searches for additional Higgs bosons concentrate on final states consisting of SM particles, final states containing beyond the SM (BSM) particles play an important role in many BSM models. In order to facilitate future searches for such final states, we develop a simplified model framework for heavy Higgs boson decays to a massive SM boson as well as one or more invisible particles. Allowing one kind of BSM mediator in each decay chain, we classify the possible decay topologies for each final sta…
We consider extensions of the Standard Model with neutral scalars in multiplets of $SU(2)$ larger than doublets. When those scalars acquire vacuum expectation values, the resulting masses of the gauge bosons $W^\pm$ and $Z^0$ are not related by $m_W = m_Z \cos{θ_W}$. In those extensions of the Standard Model the oblique parameters $S$ and $U$, when computed at the one-loop level, turn out to be either gauge-dependent or divergent. We show that one may eliminate this problem by modifying the Feynman rules of the Standard Model for some vertices containing the Higgs boson; the modifying factors …
We compute the renormalisation factors (Z-matrices) of the $ΔF=2$ four-quark operators needed for Beyond the Standard Model (BSM) kaon mixing. We work with nf=2+1 flavours of Domain-Wall fermions whose chiral-flavour properties are essential to maintain a continuum-like mixing pattern. We introduce new RI-SMOM renormalisation schemes, which we argue are better behaved compared to the commonly-used corresponding RI-MOM one. We find that, once converted to MS, the Z-factors computed through these RI-SMOM schemes are in good agreement but differ significantly from the ones computed through the RI…
The recent measurement by the CDF Collaboration of the $W$ boson mass is in significant tension with the Standard Model expectation, showing a discrepancy of seven standard deviations. A larger value of $m_W$ affects the global electroweak fit, particularly the best-fit values of the Peskin-Takeuchi parameters $S$, $T$ (and perhaps $U$) that measure oblique corrections from new physics. To meet this challenge, we propose some simple models capable of generating non-negative $S$ and $T$, the latter of which faces the greatest upward pressure from the CDF measurement in scenarios with $U=0$. Our…
We study the potential for precision electroweak (EW) measurements and beyond-the-Standard Model (BSM) searches using cross-section asymmetries in neutral-current (NC) deep inelastic scattering at the electron-ion collider (EIC). Our analysis uses a complete and realistic accounting of systematic errors from both theory and experiment and considers the potential of both proton and deuteron beams for a wide range of energies and luminosities. We also consider what can be learned from a possible future positron beam and a potential ten-fold luminosity upgrade of the EIC beyond its initial decade…
We identify two types of well-motivated, so-far experimentally unexplored LHC signatures of extended Higgs sectors: First, Higgs-to-Higgs decay signatures that involve (at least) two Beyond-the-Standard Model (BSM) neutral scalar bosons, $ϕ_i \to ϕ_j ϕ_k$. These signatures are discussed in the framework of the Two-Real-Singlet-Model (TRSM), which can furthermore exhibit cascades of Higgs-to-Higgs decays leading to multi-Higgs final states. Second, the charged Higgs boson decay to a W boson and a neutral BSM Higgs boson, which can easily become the dominant decay within the Two-Higgs-Doublet-Mo…
We formulate a generalization of Higgs effective field theory (HEFT) including arbitrary number of extra neutral and charged Higgs bosons (generalized HEFT, GHEFT) to describe non-minimal electroweak symmetry breaking models. Using the geometrical form of the GHEFT Lagrangian, which can be regarded as a nonlinear sigma model on a scalar manifold, it is shown that the scalar boson scattering amplitudes are described in terms of the Riemann curvature tensor (geometry) of the scalar manifold and the covariant derivatives of the potential. The coefficients of the one-loop divergent terms in the ob…
Davidson College（戴维森学院）；Florida State University（佛罗里达州立大学）
One of the goals of current particle physics research is to obtain evidence for new physics, that is, physics beyond the Standard Model (BSM), at accelerators such as the Large Hadron Collider (LHC) at CERN. The searches for new physics are often guided by BSM theories that depend on many unknown parameters, which, in some cases, makes testing their predictions difficult. In this paper, machine learning is used to model the mapping from the parameter space of the phenomenological Minimal Supersymmetric Standard Model (pMSSM), a BSM theory with 19 free parameters, to some of its predictions. Ba…
The program HiggsBounds is a well-established tool for testing Beyond-the-Standard Model (BSM) theories with an extended Higgs sector against experimental limits from collider searches at LEP, Tevatron and LHC. Thus far, it could be applied to any neutral or charged Higgs bosons originating from the modified Higgs sector. Implicitly, these particles were assumed to exhibit a somewhat hierarchical Yukawa structure as present in the Standard Model, where in particular the couplings to first generation fermions could be neglected. In this work, we extend the HiggsBounds functionalities to go beyo…
Many theories beyond the standard model (BSM) contain new CP-odd and CP-even neutral scalars $ϕ= \{A,H\}$, and new vector-like fermions ($ψ_{VL}$). The couplings of the CP-odd scalar $A$ to two standard model (SM) gauge bosons cannot occur from renormalizable operators in a CP-conserving sector, but can be induced at the quantum loop level. We compute these effective couplings at the 1-loop level induced by the SM fermions and vector-like fermions, present analytical expressions for them, and plot them numerically. Using the 8~TeV Large Hadron Collider (LHC) $γγ$, $τ^{+} τ^{-}$ and $t \bar t$ …
We explore the parameter space of the type-II two-Higgs-doublet model with softly broken Z2 symmetry, allowing for CP violation in the scalar potential. Imposing theory-motivated and experimentally-driven constraints, we show that as the CP-violating phases are increased, only small regions of parameter space survive, including regions slightly away from the alignment limit. Electroweak oblique parameters and electric dipole moments emerge as most restrictive constraints. We show that imposing these constraints (as well as theoretical bounds such as perturbativity) the masses of the charged an…
Neutrinos are neutral, spin-$\frac{1}{2}$ particles which undergo only weak interactions. The experimentally observed phenomenon of neutrino oscillation establishes the fact that neutrinos are massive and there is mixing between different neutrino flavours. This constitutes the first unambiguous hint towards the physics Beyond Standard Model (BSM). In the BSM theories, the neutrino mass terms in the Lagrangian lead to the non-diagonal neutrino mass matrix in the flavour basis which depends on neutrino mass and mixing parameters. Thus knowledge of the neutrino oscillation parameters and underst…
We explore the phenomenology of models containing one Vector-Like Quark (VLQ), $t'$, which can decay into the Standard Model (SM) top quark, $t$, and a new spin-0 neutral boson, $S$, the latter being either a scalar or pseudoscalar state. We parametrise the underlying interactions in terms of a simplified model which enables us to capture possible Beyond the SM (BSM) scenarios. We discuss in particular three such scenarios: one where the SM state is supplemented by an additional scalar, one which builds upon a 2-Higgs Doublet Model (2HDM) framework and another which realises a Composite Higgs …
We analyse the Higgs sector of an $S_3$ model with three Higgs doublets and no CP violation. After electroweak breaking there are nine physical Higgs bosons, one of which corresponds to the Standard Model one. We study the scalar and gauge sectors of this model, taking into account the conditions set by the minimisation and stability of the potential. We calculate the masses, trilinear and quartic Higgs-Higgs, and Higgs-gauge couplings. We consider two possible alignment scenarios, where only one of the three neutral scalars has couplings to the gauge bosons and corresponds to the SM Higgs, an…
We enumerate various effective couplings that contribute to the mixings between an exotic vector boson $Z^{\prime}$ and the neutral electroweak vector bosons. The miscellaneous mixing patterns can be evaluated perturbatively. The effective oblique parameters $S^{\prime}$, $T^{\prime}$, and $U^{\prime}$ are calculated to compare with the electroweak precision test results. With the contributions to the non-negligible $U^{\prime}$ parameter from the $ε_{B,W}$ parameters and the aid of some other parameters to cancel the negative $T^{\prime}$, the recent CDF $W$-mass anomaly can therefore be expl…
The model of heavy neutral leptons (HNLs) is one of the well-motivated models beyond the standard model (BSM) from both theoretical and phenomenological point of views. It is an indispensable ingredient to explain the puzzle of tiny neutrino masses and the origin of the matter-antimatter asymmetry in our Universe, based on the models in which the simplest Type-I seesaw mechanism can be embedded. The HNL with a mass up to the electroweak scale is an attractive scenario which can be readily tested in present or near-future experiments including the LHC. In this work, we study the decay rates of …
We investigate the potential of the Large Hadron Collider (LHC) to probe one of the most compelling Beyond the Standard Model (BSM) frameworks --- Walking Technicolor (WTC), involving strong dynamics and having a slowly running (walking) new strong coupling. For this purpose we use recent LHC Run2 data to explore the full parameter space of the minimal WTC model using dilepton signatures from heavy neutral $Z^{\prime}$ and $Z^{\prime\prime}$ resonances predicted by the model. This signature is the most promising one for discovery of WTC at the LHC for the low-intermediate values of the $\tilde…
