arXiv subjects

Adam Martin

Publications and source records attributed to Adam Martin.

At least 19 recordsLinked to original sources

arXiv2026

Anomalous triple gauge couplings in the light of dimension-8 operators in $W^+W^-$

We compare the size of dimension-8 effects on $W^+W^-$ production at the LHC arising from the $q\bar q$ and $\gamma\gamma$ initial states. In particular, we consider bosonic operators, which contribute to the anomalous triple and quadruple gauge couplings. The relevant dimension-6 and dimension-8 operators are matched to the anomalous triple gauge couplings that contribute to the $q\bar q$ channel, allowing for the resummation of large logarithmic contributions arising in the presence of a jet-veto through the program MCFM-RE. For the $\gamma\gamma$ channel, which receives contributions from both triple and quadruple gauge couplings, such resummation can be performed through the program MadGraph, by simply setting the factorisation scale to the jet-veto scale. We find that, when neglecting fermionic dimension-8 operators, the $\gamma\gamma$ channel has a dominant bosonic dimension-8 contribution and this channel can be used to understand the range of validity of the Effective Field Theory. With this in mind, and carefully considering theoretical and experimental uncertainties, we provide constraints on higher dimensional operators using current and future data.

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arXiv2026

EFT Validity and Truncation Uncertainty from few Nuisance Parameters

An observable in an Effective Field Theory (EFT) is an expansion in a set of small parameters, no different than any other perturbation series. Truncating such a series expansion leaves the leading dropped term as the dominant source of error, and that term itself contains a calculable portion. We explore the partial calculation of this next-order error, available at dim-6$^2$ in SMEFT with no additional tools needed to simulate it, and explore how to efficiently use that partial calculation to model the next-order uncertainty in full using a minimal number of nuisance parameters. This estimate of the uncertainty of the EFT signal rate naturally imposes EFT validity by ensuring that bounds are driven by kinematic regions where truncation uncertainties are parametrically smaller than the signal. We incorporate the calculable dim-6$^2$ piece into the signal and cover the remaining higher-dimension uncertainty with a small set of nuisance parameters derived from a scan over Wilson-coefficient values. Our algorithm to determine the relevant nuisance parameters and distributions is automation-friendly and applies to arbitrary truncation choices. We then provide multiple examples of its implementation in high-energy collider processes focused on SMEFT truncated at $\mathcal{O}(\Lambda^{-2})$, where the dim-6$^2$ piece is used to estimate the full $\mathcal O(\Lambda^{-4})$ dependence. In the examples considered here the reduction of nuisance parameters is appreciable, generically reducing the nuisance parameter count by an order of magnitude compared to na\"ive estimates.

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arXiv2026

Geometric Amplitudes: A Covariant Functional Approach for Massless Scalar Theories

Functional geometry is a framework using concepts from geometry to understand the invariance of amplitudes in quantum field theory under a large class of field redefinitions, including those involving derivatives. It is inspired by recursion relations among correlation functions, where higher-point functions depend iteratively upon smaller correlators. Previous work has shown that, with suitable modifications, these correlation functions become covariant under field redefinitions, provided they are evaluated at the physical ``on-shell" point. In this paper, we show how to further modify correlation functions in massless scalar field theories to achieve ``off-shell" covariance. We investigate the conditions required for the framework to work and discuss the geometric interpretation of this construction -- which prioritizes the covariant transformation of observables under field redefinitions over the role of a metric tensor and its derivatives. While analogous modifications may exist for massive theories, we show that framework developed here does not extend straightforwardly to that case.

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arXiv2026

Higgs decays to four leptons to $\mathcal{O}(1/\Lambda^4)$ in SMEFT

We study the decays $h \to \ell \bar{\ell} \left(Z \to \ell' \bar{\ell'}\right)$ and $h\to\ell\bar{\nu}_\ell\nu_{\ell'}\bar{\ell'}$ within the SMEFT framework and including effects up to $\mathcal O(1/\Lambda^4)$, where $\Lambda$ is the new physics scale suppressing higher dimensional operators. To work to this order, we must include the square of dimension-six operators and the interference of dimension-eight operators with the Standard Model. We study angular asymmetries and other differential decay observables and determine which are most sensitive to $\mathcal O(1/\Lambda^4)$ effects. While new kinematic structures arising in higher dimensional operators have the potential to induce novel angular dependency, we find this does not occur for $h\to\ell\bar{\ell}\left(Z\xrightarrow{}\ell'\bar{\ell'}\right)$. For $h \to \ell \bar{\nu}_\ell \nu_{\ell'} \bar{\ell'}$, new angular dependencies do arise at $\mathcal O(1/\Lambda^4)$, though they require a fully reconstructible (meaning we can go to the Higgs rest frame) final state. For non-reconstructible final states such as $\ell \bar{\nu}_\ell \nu_{\ell'} \bar{\ell'}$, we must study Higgs production and decay together with the appropriate observables, which we find obscures the new angular effects.

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arXiv2026

Probing EFT breakdown in the tails of $W^+ W^-$ observables

In this letter, we test clipping effective field theory (EFT) simulations as a method of ensuring EFT validity. The procedure imposes that, at the level of the simulation, the invariant mass of a $W^+W^-$ pair $M_{WW}$ is less than the new physics scale $\Lambda$. We compare this to two other methods, comparison bin by bin of dimension-6 and dimension-8 squared contributions and implementing a cut on data. We find that setting $M_{WW} < \Lambda$ is not strict enough to ensure that the hierarchy of EFT operators is respected for dimension-6 and dimension-8 contributions. We also show that, even when using a stricter cut on $M_{WW}$, due to different correlations between $M_{WW}$ and $M_{e\mu}$ at different EFT orders, the bins in $M_{e\mu}$ (the invariant mass of the leptons originating from $W$ decays) used in an EFT fit may not truly be in the regime of EFT validity when performing a dimension-6 fit with $M_{WW} < \Lambda$. We also explore the correlations of three transverse mass observables: $M_{T1}, M_{T2}$ and $M_{T3}$, finding that $M_{T1}$ and $M_{T3}$ follow the $M_{WW}$ distribution more closely than $M_{e\mu}$. We present sensitivity studies using both the $M_{T3}$ distribution and $M_{e\mu}$ distribution. We test implementing an experimental cut on $M_{T3}$ in place of clipping the EFT simulation at $M_{WW} < \Lambda$. We finally comment that adding $M_{WW} < \Lambda$ cuts only to the EFT simulation could be interpreted as modifying the SMEFT expansion by a form factor and could therefore impact the model independence of EFT fits under this procedure.

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arXiv2025

Phenomenology of Fractionally Charged Particles: Two Reps Are Better Than One

We continue our study of fractionally charged particles (FCPs) -- particles carrying electric charge a multiple of $e/6$. Discovering an FCP would inform us about both Standard Model physics (what the true gauge group and the one-form global symmetry are) and Beyond the Standard Model physics (ruling out many unified theories), which makes them a high-stakes target for collider searches. Here we find that with two FCPs there are vastly richer phenomenologies compared to the single-particle extensions we previously studied. Stringent constraints on colored FCPs can be dramatically weakened when decays are open; conversely the cross sections of the least visible species can be enlarged by up to $\sim 10^3$, increasing their discovery potential enormously at the LHC and milliQan. Overall, these simple models motivate performing searches for FCPs produced along with jets or leptons, and highlight 'free' discovery potential in reanalyzing existing missing-energy datasets for low-quality tracks.

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arXiv2025

Non-factorizable Superamplitudes for Massive N = 1 Superstates

In this paper we study non-factorizable N = 1 superamplitudes for massive chiral superstates. We demonstrate how little group scaling and the supersymmetric Ward identities determine the form of non-factorizable massless superamplitudes, then extrapolate to massive superamplitudes by requiring they reduce to the massless form when we send all masses to zero. This technique does not depend on whether or not the superstates are self-conjugate (so that the fermionic components are either Dirac or Majorana) or whether the superamplitude is dressed with a form-factor.

hep-th↗

arXiv2025

Energy-Enhanced Expansion of the Standard Model Effective Field Theory

We formalize energy-scaling arguments in the Standard Model Effective Field Theory (SMEFT) to estimate effects of operators up to dimension ten. Introducing a classification based on the number of external legs and an energy-counting parameter, we establish a dual expansion in $v/\Lambda$ and $E/\Lambda$. Extending to four-, five-, and six-particle vertices, our framework highlights energy-enhanced operators that dominate high-energy processes at the HL-LHC. This organization streamlines experimental analyses to only include operators with energetic impact in their analyses and enhances the discoverability of new physics within the SMEFT framework.

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arXiv2024

Dimension-8 operators in $W^+W^-$ production via gluon fusion

We investigate the impact of dimension-8 operators on $W^+W^-$ production at the LHC for the incoming gluon-gluon channel. To this end, we have identified all dimension-8 CP-even operators contributing to the process in question, and computed the corresponding tree-level helicity amplitudes for fully-leptonic decays of the $W$ bosons. These are implemented in the program MCFM-RE, which automatically incorporates the effect of a jet-veto to reduce the otherwise overwhelming $t\bar t$ background. We find that, unless we break the hierarchy of the effective field theory (EFT), the interference of the dimension-8 operators with the Standard Model is negligible across the considered distributions. This justifies including the square of dimension-6 operators when performing EFT fits with this channel. We then present new constraints on CP-even and CP-odd dimension-6 operators within the EFT regime. Lastly, we postulate a scenario in which the hierarchy of the EFT is broken, justified by the strong constraints on dimension-6 operators from existing on-shell Higgs data. In this scenario, we discuss the constraints that can be reasonably set on CP-even dimension-8 operators with current and future data. We remark that the effect of the jet-veto on the ability to constrain new physics in the $W^+W^-$ channel is quite dramatic and must be properly taken into account.

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arXiv2024

Energy-Enhanced Dimension Eight SMEFT Effects in VBF Higgs production

We study Higgs boson production via vector boson fusion at the LHC, focusing on the process $pp \to H + jj$ and capturing the leading energy-enhanced contributions within the Standard Model Effective Field Theory (SMEFT) up to order $1/\Lambda^4$. Employing energy-scaling arguments, we predict the magnitude of each higher-dimensional operator's contribution. Utilizing the geometric formulation of SMEFT, our analysis incorporates dimension-eight operators not previously considered. We find that the kinematics of vector boson fusion - characterized by two highly forward jets - tend to suppress contributions from higher-dimensional operators, requiring a lower scale $\Lambda$ for SMEFT effects to become observable. This suggests that the SMEFT remains valid for lower $\Lambda$ than expected. Combined with the fact that LEP constrains the dimension-six operators with the most considerable impact on vector boson fusion, a regime exists where dimension-eight operators can have significant effects. In many cases, these dimension-eight operators also influence associated production processes like $pp \to H V(jj)$, though differences in analysis cuts and kinematics mean this is not always the case. Our findings provide insights that could refine the search for SMEFT signals in collider experiments.

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arXiv2024

EFT Workshop at Notre Dame

The LPC EFT workshop was held April 25-26, 2024 at the University of Notre Dame. The workshop was organized into five thematic sessions: "how far beyond linear" discusses issues of truncation and validity in interpretation of results with an eye towards practicality; "reconstruction-level results" visits the question of how best to design analyses directly targeting inference of EFT parameters; "logistics of combining likelihoods" addresses the challenges of bringing a diverse array of measurements into a cohesive whole; "unfolded results" tackles the question of designing fiducial measurements for later use in EFT interpretations, and the benefits and limitations of unfolding; and "building a sample library" addresses how best to generate simulation samples for use in data analysis. This document serves as a summary of presentations, subsequent discussions, and actionable items identified over the course of the workshop.

hep-ex↗

arXiv2024

Fractionally Charged Particles at the Energy Frontier: The SM Gauge Group and One-Form Global Symmetry

The observed Standard Model is consistent with the existence of vector-like species with electric charge a multiple of $e/6$. The discovery of a fractionally charged particle would provide nonperturbative information about Standard Model physics, and furthermore rule out some or all of the minimal theories of unification. We discuss the phenomenology of such particles and focus particularly on current LHC constraints, for which we reinterpret various searches to bound a variety of fractionally charged representations. We emphasize that in some circumstances the collider bounds are surprisingly low or nonexistent, which highlights the discovery potential for these species which have distinctive signatures and important implications. We additionally offer pedagogical discussions of the representation theory of gauge groups with different global structures, and separately of the modern framework of Generalized Global Symmetries, either of which serves to underscore the bottom-up importance of these searches.

hep-ph↗

arXiv2024

Basis for Non-Factorizable Superamplitudes in N = 1 Supersymmetry

In this paper we develop a semi-standard Young tableau (SSYT) approach to construct a basis of non-factorizable superamplitudes in N = 1 massless supersymmetry. This amplitude basis can be directly translated to a basis for higher dimensional supersymmetric operators, yielding both the number of independent operators and their form. We deal with distinguishable (massless) chiral/vector superfields at first, then generalize the result to the indistinguishable case. Finally, we discuss the advantages and disadvantages of this method compared to the previously studied Hilbert series approach.

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arXiv2024

Drell-Yan Bounds on Gapped Continuum Spectra

Theories with gapped continuum spectra have gotten some attention, either as pure 4D models like unparticles, or in 5D realizations as certain soft walls constructions. In this paper, we derive experimental bounds from Drell-Yan processes ($pp \to \ell^+\ell^-$, $pp \to \ell^\pm \nu$) in a particular scenario where the electroweak bosons propagate in an extra dimension that produces a propagator with a continuum spectrum, on top of the isolated corresponding Standard Model pole. Using current LHC data we put a lower bound on the gap of 4.2 TeV (expected), 6.2 TeV (observed, bins with $< 10$ events combined) at 95\% CL, with some dependence in the observed limit on how low statistics bins are treated. We also study the limits for HL-LHC.

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arXiv2023

A case study of SMEFT $\mathcal O(1/\Lambda^4)$ effects in diboson processes: $pp \to W^\pm(\ell^\pm \nu) \gamma$

In this paper we explore $pp \to W^\pm (\ell^\pm \nu) \gamma$ to $\mathcal O(1/\Lambda^4)$ in the SMEFT expansion. Calculations to this order are necessary to properly capture SMEFT contributions that grow with energy, as the interference between energy-enhanced SMEFT effects at $\mathcal O(1/\Lambda^2)$ and the Standard Model is suppressed. We find that there are several dimension eight operators that interfere with the Standard Model and lead to the same energy growth, $\sim \mathcal O(E^4/\Lambda^4)$, as dimension six squared. While energy-enhanced SMEFT contributions are a main focus, our calculation includes the complete set of $\mathcal O(1/\Lambda^4)$ SMEFT effects consistent with $U(3)^5$ flavor symmetry. Additionally, we include the decay of the $W^\pm \to \ell^\pm\nu$, making the calculation actually $\bar q q' \to \ell^\pm \nu \gamma$. As such, we are able to study the impact of non-resonant SMEFT operators, such as $(L^\dag\bar\sigma^\mu \tau^I\, L) (Q^\dag\bar\sigma^\nu \tau^I\, Q)\, B_{\mu\nu}$, which contribute to $\bar q q' \to \ell^\pm \nu \gamma$ directly and not to $\bar q q' \to W^\pm \gamma$. We show several distributions to illustrate the shape differences of the different contributions.

hep-ph↗

arXiv2023

Hidden U(N) Symmetry behind N=1 Superamplitudes

In this paper we develop a Young diagram approach to constructing higher dimensional operators formed from massless superfields and their superderivatives in $\mathcal{N}=1$ supersymmetry. These operators are in one-to-one correspondence with non-factorizable terms in on-shell superamplitudes, which can be studied with massless spinor helicity techniques. By relating all spin-helicity variables to certain representations under a hidden $U(N)$ symmetry behind the theory, we show each non-factorizable superamplitude can be identified with a specific Young tableau. The desired tableau is picked out of a more general set of $U(N)$ tensor products by enforcing the supersymmetric Ward identities. We then relate these Young tableaux to higher dimensional superfield operators and list the rules to read operators directly from Young tableau. Using this method, we present several illustrative examples.

hep-th↗

arXiv2023

More accurate $\sigma(\mathcal{G} \,\mathcal{G}\rightarrow h)$, $\Gamma(h \rightarrow \mathcal{G} \,\mathcal{G}, \mathcal{A} \mathcal{A}, \bar{\Psi} {\Psi})$ and Higgs width results via the geoSMEFT

We develop Standard Model Effective Field Theory (SMEFT) predictions of $\sigma(\mathcal{G} \,\mathcal{G}\rightarrow h)$, $\Gamma(h \rightarrow \mathcal{G} \,\mathcal{G})$, $\Gamma(h \rightarrow \mathcal{A} \mathcal{A})$ to incorporate full two loop Standard Model results at the amplitude level, in conjunction with dimension eight SMEFT corrections. We simultaneously report consistent $\Gamma(h \rightarrow \bar{\Psi} {\Psi})$ results including leading QCD corrections and dimension eight SMEFT corrections. This extends the predictions of the former processes $\Gamma, \sigma$ to a full set of corrections at $\mathcal{O}(\bar{v}_T^2/\Lambda^2 (16 \pi^2)^2)$ and $\mathcal{O}(\bar{v}_T^4/\Lambda^4)$, where $\bar{v}_T$ is the electroweak scale vacuum expectation value and $\Lambda$ is the cut off scale of the SMEFT. Throughout, cross consistency between the operator and loop expansions is maintained by the use of the geometric SMEFT formalism. For $\Gamma(h \rightarrow \bar{\Psi} {\Psi})$, we include results at $\mathcal{O}(\bar{v}_T^2/\Lambda^2 (16 \pi^2))$ in the limit where subleading $m_\Psi \rightarrow 0$ corrections are neglected. We clarify how gauge invariant SMEFT renormalization counterterms combine with the Standard Model counter terms in higher order SMEFT calculations when the Background Field Method is used. We also update the prediction of the total Higgs width in the SMEFT to consistently include some of these higher order perturbative effects.

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arXiv2023

Counting Operators in $N=1$ Supersymmetric Gauge Theories

Following a recent publication, in this paper we count the number of independent operators at arbitrary mass dimension in $N=1$ supersymmetric gauge theories and derive their field and derivative content. This work uses Hilbert series machinery and extends a technique from our previous work on handling integration by parts redundancies to vector superfields. The method proposed here can be applied to both abelian and non-abelian gauge theories and for any set of (chiral/antichiral) matter fields. We work through detailed steps for the abelian case with single flavor chiral superfield at mass dimension eight, and provide other examples in the appendices.

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