arXiv subjects

Linda M. Carpenter

Publications and source records attributed to Linda M. Carpenter.

At least 19 recordsLinked to original sources

arXiv2026

Strong-Weak Bi-Adjoints, Gluon-W resonances, and new asymmetric LHC production processes

We study a novel production and decay mechanism for a bi-adjoint spin zero particle in the ($8,3,0$) representation of the Standard Model gauge groups. This work is part of a series studying new production processes for exotic particles in higher representations of Standard Model color and weak charge. Here, we study a specific new dimension 5 effective operator model which couples an exotic bi-adjoint scalar field to the SU(3) and SU(2) field strength tensors. The W-gluon resonant decay of the charged component of this new exotic field is explored. We discuss LHC production modes of both the charged and neutral bi-adjoint states and find a new single production mode for the charged state. This is the dominant LHC production mode for TeV-scale masses. We introduce a new HL-LHC search in which a single bi-adjoint is produced in association with a hard forward quark jet from asymmetric W-gluon fusion. This search yields a 5-sigma discovery potential for bi-adjoint masses up to 3 TeV for 10 TeV scalar effective operator cutoffs. We also find 2-sigma sensitivity at the HL-LHC for bi-adjoint masses up to 4 TeV and effective cutoffs in the 15 TeV range for the full 3 inverse atto-barn data set.

hep-ph↗

arXiv2026

The quark-lepton portal beyond leptoquarks

We explore models where single new exotic states interact with the Standard Model through an asymmetric Standard Model portal with couplings to at least one quark and one lepton. All effective operators up to dimension six where such interactions couple the SM to spin 0 and spin 1/2 particles are written down, and the exotic states accessible through the portal are identified. We note interactions that couple the SM to new particles with exotic combinations of baryon and lepton numbers, states of higher electric charge, and particles with unusual SM charge, including states in higher-dimensional representations of both SU(3) and SU(2). Finally, we discuss the phenomenology of these interactions, including novel particle decays, and we classify some of the collider production modes for exotic states at the LHC, LHeC and muon colliders.

hep-ph↗

arXiv2026

Dark matter with exotic mediators: The diquark portal

In this work we build out complete mediator sectors for models of frustrated dark matter (fDM), a new paradigm in which fermionic dark matter couples to the Standard Model (SM) through a scalar-fermionic mediator pair. The fDM paradigm allows great freedom in the charge assignments of the mediators: it accommodates any representation of the SM gauge group provided that the scalar and fermionic mediators have the same charges. In this paper, we write down all renormalizable models in which the mediator(s) make contact with the SM through pairs of quarks, a model space we refer to as the diquark portal. The mediators in this portal may be singlets, triplets, sextets, or octets of the color group $\mathrm{SU}(3)_{\text{c}}$. The mediators may additionally be in non-trivial representations of the weak group $\mathrm{SU}(2)_{\text{L}}$, including doublet and triplet representations, depending on the mediators' color charge. In addition to writing the complete set of renormalizable Lagrangians, we categorize the general collider phenomenology of the models and discuss pair- and single-production LHC signatures of the mediator sectors.

hep-ph↗

arXiv2025

The Lepton-Gluon Portal Beyond Lepto-Gluons

We explore models where single new exotic states interact with the Standard Model through an asymmetric Standard Model portal with couplings to at least one gluon and one lepton. We consider the complete set of effective operators up to dimension 6, and examine a few additional dimension 7 operators that contain interesting field content or potential collider signals. The lepton-gluon portal allows access to exotic states with an interesting range of SU(3) and SU(2) quantum numbers. Finally, we explore potential single-production modes and their phenomenological signatures at colliders.

hep-ph↗

arXiv2025

Portals to New Physics: The W-Quark Portal

We explore new EFT operators where single new exotic states interact with the Standard Model through an asymmetric Standard Model portal with couplings to at least one quark and one W boson. Effective operators up to dimension 6 are considered, and we specify SM charges of all new states accessible through this portal. We explore our interactions by detailing possible collider production processes at e-p and p-p colliders. Finally, we study the LHC production of a new weak-quadruplet SU(3) fundamental fermion which can be singly produced in association with a SM quark through W-quark portal processes.

hep-ph↗

arXiv2025

t-channel dark matter at the LHC -- a whitepaper

This report, summarising work achieved in the context of the LHC Dark Matter Working Group, investigates the phenomenology of $t$-channel dark matter models, spanning minimal setups with a single dark matter candidate and mediator to more complex constructions closer to UV-complete models. For each considered class of models, we examine collider, cosmological and astrophysical implications. In addition, we explore scenarios with either promptly decaying or long-lived particles, as well as featuring diverse dark matter production mechanisms in the early universe. By providing a unified analysis framework, numerical tools and guidelines, this work aims to support future experimental and theoretical efforts in exploring $t$-channel dark matter models at colliders and in cosmology.

hep-ph↗

arXiv2024

Unusual portals to new exotics, the W-gluon portal

We explore models where new light exotic states interact with the Standard Model through an asymmetric di-boson portal with one gluon and one W boson. We consider the complete set of effective operators up to dimension 6 which couple a single light exotic (LEX) state to at least one W boson and 1 gluon. Other Standard Model particles may also be present in the interactions. We discover that the W-gluon portal allows us to access a large array of exotic states in non-trivial representations of SU(3) and SU(2). We discuss new single production collider modes and phenomenological signatures for these light exotic states at LHC and e-p colliders.

hep-ph↗

arXiv2024

Leptonic signatures of color-sextet scalars II: Exploiting unique large-$E_{\text{T}}^{\text{miss}}$ signals at the LHC

The diverse and distinct collider phenomenology of color-sextet scalars motivates thorough investigation of their effective couplings to the Standard Model at the LHC. Some of the more unique sextet signals involve not only jets but also leptons. In previous work, we proposed an LHC search for color-sextet scalars in a channel with jets and a hard opposite-sign lepton pair, which results from a dimension-six coupling. In this sequel we study the counterpart processes with neutrinos, which produce jets in association with missing transverse energy ($E_{\text{T}}^{\text{miss}}$) in addition to possible leptons. We consider multiple search channels, including both single and pair sextet production, all characterized by significant missing energy and some featuring distinctive kinematic features. Our multifaceted study consists of three reinterpreted existing searches and a joint-likelihood analysis designed by us to maximize HL-LHC sensitivity to single sextet production. We show that our dedicated strategy in the jets + lepton + $E_{\text{T}}^{\text{miss}}$ channel can supersede today's limits from reinterpreted searches, and we make sensitivity projections for the HL-LHC. Altogether, our analysis can exclude sextet scalars lighter than 4.4 TeV or probe effective cutoffs as high as 16.8 TeV.

hep-ph↗

arXiv2024

Taking aim at the wino-higgsino plane with the LHC

In this work we explore multiple search strategies for higgsinos and mixed higgsino-wino states in the MSSM and project the results onto the $(μ,M_2)$ plane. Assuming associated production of higgsino-like pairs with a $W/Z$ boson, we develop a search in a channel characterized by a hadronically tagged vector boson accompanied by missing energy. We use as our template an ATLAS search for dark matter produced in association with a hadronically decaying vector boson, but upgrade the search by implementing a joint likelihood analysis, binning the missing transverse energy distribution, which greatly improves the search sensitivity. For higgsino-like states (more than 96% admixture) we find sensitivity to masses up to 550 GeV. For well-mixed higgsino-wino states (70-30% higgsino) we still find sensitivities above 300 GeV. Using this newly proposed search, we draw a phenomenological map of the wino-higgsino parameter space, recasting several complementary searches for disappearing tracks, soft leptons, trileptons, and hadronic diboson events in order to predict LHC coverage of the $(μ,M_2)$ mass plane at integrated luminosities of up to $3\,\text{ab}^{-1}$. Altogether, the full run of the HL-LHC can exclude much of the "natural" ($μ,M_2 <$ 500 GeV) wino-higgsino parameter space.

hep-ph↗

arXiv2023

LEX-EFT: The Light Exotics Effective Field Theory

We propose the creation of a Light Exotics Effective Field Theory (LEX-EFT) catalog. LEX-EFT is a generic framework to capture all interactions between the Standard Model (SM) and all (or at least a large class of) theoretically allowed exotic states beyond the Standard Model (bSM), indexed by their SM and bSM charges. These states are light enough to be on or nearly on shell in some collider processes. This framework, which subsumes beyond the Standard Model paradigms as generally as possible, is meant to extend recent successful implementations of bSM EFTs and complement e.g. the Standard Model Effective Field Theory (SMEFT), which can capture the off-shell effects of exotic fields. In this work, we review a general method for the construction of a complete list of gauge-invariant operators involving SM interactions with light exotics via iterative tensor product decomposition, up to the desired order in mass dimension. Each operator is characterized by specific Clebsch-Gordan coefficients determined by the charge flow; we show how this charge flow affects the range of EFT validity and cross sections associated with an effective operator. We create an example catalog of exotic scalars coupling to SM gauge boson pairs, and we highlight some operators with exotic weak $\mathrm{SU}(2)_{\text{L}}$ charges that can produce spectacular LHC phenomenology. We further demonstrate the utility of the LEX-EFT approach with several examples of effects on kinematic distributions and cross sections that would not be captured by EFTs agnostic to the exotic degrees of freedom and may evade the main inclusive collider searches tailored to the existing preferred set of standard bSM theories.

hep-ph↗

arXiv2022

Leptonic signatures of color-sextet scalars

Color-sextet scalars could have an array of possible couplings to the Standard Model beyond their well known renormalizable couplings to quark pairs. The next-largest couplings these scalars might enjoy have mass dimension six, and some include electroweak fields and can therefore produce highly distinctive signals at hadron colliders. Here we study the single production of color-sextet scalars in association with a hard lepton, which results from a dimension-six coupling to leptons in addition to quarks and gluons. We identify parameter space in which these scalars decay promptly and propose a search for such particles in final states with two jets and an opposite-charge lepton pair, one member of which has high momentum. We then impose our selection criteria on the proposed signal and its leading backgrounds to project the discovery potential and exclusion limits during the next runs of the LHC. We compare our search with existing searches for leptoquarks, and we find we achieve much higher sensitivity with our tailored approach due to the unique kinematics of leptonic sextet events.

hep-ph↗

arXiv2022

Distinctive signals of frustrated dark matter

We study a renormalizable model of Dirac fermion dark matter (DM) that communicates with the Standard Model (SM) through a pair of mediators -- one scalar, one fermion -- in the representation $(\boldsymbol{6},\boldsymbol{1}, \tfrac{4}{3})$ of the SM gauge group $\text{SU}(3)_{\text{c}} \times \text{SU}(2)_{\text{L}} \times \text{U}(1)_Y$. While such assignments preclude direct coupling of the dark matter to the Standard Model at tree level, we examine the many effective operators generated at one-loop order when the mediators are heavy, and find that they are often phenomenologically relevant. We reinterpret dijet and pair-produced resonance and $\text{jets} + E_{\text{T}}^{\text{miss}}$ searches at the Large Hadron Collider (LHC) in order to constrain the mediator sector, and we examine an array of DM constraints ranging from the observed relic density $Ω_χ h^2_{\text{Planck}}$ to indirect and direct searches for dark matter. Tree-level annihilation, available for DM masses starting at the TeV scale, is required in order to produce $Ω_χ h^2_{\text{Planck}}$ through freeze-out, but loops -- led by the dimension-five DM magnetic dipole moment -- are nonetheless able to produce signals large enough to be constrained, particularly by the XENON1T experiment. In some benchmarks, we find a fair amount of parameter space left open by experiment and compatible with freeze-out. In other scenarios, however, the open space is quite small, suggesting a need for further model-building and/or non-standard cosmologies.

hep-ph↗

arXiv2022

The phenomenological cornucopia of SU(3) exotica

We introduce an effort to catalog the gauge-invariant interactions of Standard Model (SM) particles and new fields in a variety of representations of the SM color gauge group $\text{SU}(3)_{\text{c}}$. In this first installment, we direct this effort toward fields in the six-dimensional (sextet, $\boldsymbol{6}$) representation. We consider effective operators of mass dimension up to seven (comprehensively up to dimension six), featuring both scalar and fermionic color sextets. We use an iterative tensor-product method to identify the color invariants underpinning such operators, emphasizing structures that have received little attention to date. In order to demonstrate the utility of our approach, we study a simple but novel model of color-sextet fields at the Large Hadron Collider (LHC). We compute cross sections for an array of new production channels enabled by our operators, including single-sextet production and sextet production in association with photons or leptons. We also discuss dijet-resonance constraints on a sextet fermion. This example shows that there remains a wide array of fairly minimal but well motivated and unexplored models with extended strong sectors as we await the high-luminosity LHC.

hep-ph↗

arXiv2022

Changing patterns in electroweak precision with new color-charged states: Oblique corrections and the $W$ boson mass

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 models feature weak multiplets of scalars charged under $\mathrm{SU}(3)_{\text{c}} \times \mathrm{U}(1)_Y$, which cannot attain nonzero vacuum expectation values but nevertheless produce e.g. $T \neq 0$ given some other mechanism to split the electrically charged and neutral scalars. We compute the oblique corrections in these models and identify ample parameter space supporting the CDF value of $m_W$.

hep-ph↗

arXiv2022

New physics in triboson event topologies

We present a study of the sensitivity to models of new physics of proton collisions resulting in three electroweak bosons. As a benchmark, we analyze models in which an exotic scalar field $ϕ$ is produced in association with a gauge boson ($V=γ$ or $Z$). The scalar then decays to a pair of bosons, giving the process $pp\rightarrow ϕV\rightarrow V'V"V$. We interpret our results in a set of effective field theories where the exotic scalar fields couple to the Standard Model through pairs of electroweak gauge bosons. We estimate the sensitivity of the LHC and HL-LHC datasets and find sensitivity to cross sections in the 10 fb -- 0.5 fb range, corresponding to scalar masses of 500 GeV to 2 TeV and effective operator coefficients up to 35 TeV.

hep-ph↗

arXiv2022

DarkFlux: A new tool to analyze indirect-detection spectra of next-generation dark matter models

We present DarkFlux, a software tool designed to analyze indirect-detection signatures for next-generation models of dark matter (DM) with multiple annihilation channels. Version 1.0 of this tool accepts user-generated models with $2\to 2$ tree-level dark matter annihilation to pairs of Standard Model (SM) particles and analyzes DM annihilation to $γ$ rays. The tool consists of three modules -- the annihilation fraction module, the flux module, and the analysis module -- which can be run in a loop in order to scan over DM mass if desired. [A description of each module is available in the full abstract.] DarkFlux v1.0 compares the total $γ$-ray flux to a joint-likelihood analysis of fifteen dwarf spheroidal galaxies (dSphs) analyzed by the $Fermi$-LAT collaboration. DarkFlux automatically provides data tables and can plot the output of the three modules. In this manual, we briefly motivate this indirect-detection computer tool and review the essential DM physics. We then describe the several modules of DarkFlux in greater detail. Finally, we show how to install and run DarkFlux and provide two worked examples demonstrating its capabilities.

hep-ph↗

arXiv2022

Exploring the phenomenology of weak adjoint scalars in minimal $R$-symmetric models

We examine the phenomenology of the scalar fields in weak and Higgs sectors of minimal $R$-symmetric models, in particular the 'swino' and 'sbino', the scalar partners to the chiral fields that marry the electroweak gauge bosons in Dirac gaugino models. These fields are in adjoint representations of $SU(2)$ and $U(1)$ and have both $CP$-even and $CP$-odd components. The interactions of these new states are summarized, and decay widths are computed analytically to one loop order. We discuss the tree level contributions of these new states to the mass spectrum of MSSM sfermions. We also explore production cross sections and decay signatures at colliders for several chosen benchmarks. We find that large regions of parameter space are unconstrained by present collider data.

hep-ph↗

arXiv2022

$t\bar{t}t\bar{t}$ signatures through the lens of color-octet scalars

We reinterpret two recent LHC searches for events containing four top quarks ($t\bar{t}t\bar{t}$) in the context of supersymmetric models with Dirac gauginos and color-octet scalars (sgluons). We explore whether sgluon contributions to the four-top production cross section $σ(pp \to t\bar{t}t\bar{t})$ can accommodate an excess of four-top events recently reported by the ATLAS collaboration. We also study constraints on these models from an ATLAS search for new phenomena with jets and missing transverse energy ($E_{\text{T}}^{\text{miss}}$) sensitive to signals with four top quarks. We find that these two analyses provide complementary constraints, with the jets + $E_{\text{T}}^{\text{miss}}$ search exceeding the four-top cross section measurement in sensitivity for sgluons heavier than about 800 GeV. We ultimately find that either a scalar or a pseudoscalar sgluon can currently fit the ATLAS excess in a range of reasonable benchmark scenarios, though a pseudoscalar in minimal Dirac gaugino models is ruled out. We finally offer sensitivity projections for these analyses at the HL-LHC, mapping the $5σ$ discovery potential in sgluon parameter space and computing exclusion limits at 95% CL in scenarios where no excess is found.

hep-ph↗