arXiv subjects

Marc Riembau

Publications and source records attributed to Marc Riembau.

At least 19 recordsLinked to original sources

arXiv2026

Bump Hunting Inside Jets with Energy Correlators

Energy correlators exhibit well-understood scaling behavior in the collinear limit, governed by perturbative QCD dynamics. We explore how this scaling regime is broken by new physics, converting precise energy correlator measurements into a broadband search for new physics. Under generic assumptions, unitarity and positivity are sufficient to classify and constrain the relevant signatures, which imprint an angular resonance on top of this smoothly scaling background. This converts the search into bump hunting within jets. As a proof of principle, we derive projected LHC sensitivity for a light hadrophilic $Z'$, finding competitive constraints with existing searches.

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arXiv2025

Energy Correlators of Spinning Sources

The $N$-point energy correlator measures the energy flux through $N$ detectors. We present a general framework that characterizes its full angular dependence in a series of \textit{spinning energy correlators}. These spinning correlators resurrect the angular momentum structure of both the source and the detector configuration, lost otherwise in inclusive measurements. We demonstrate that unitarity and energy positivity confine these correlators to a sharply bounded region, with the boundary realized by extremal correlators generated by pure spin states. We present a first calculation of spinning energy correlators in QCD as well as spinning energy-charge correlators. Their enhanced insensitivity to infrared dynamics opens up a new set of observables that directly probe the hard part of the scattering. Finally, we provide generalized sum rules, extended to spinning correlators and to conserved charges beyond energy.

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arXiv2025

Flow between extremal one-point energy correlators in QCD

The energy density generated by a vector current is characterized by a single parameter $a_{\mathcal{E}}$ bounded by unitarity to $-1/2 \leq a_{\mathcal{E}} \leq 1$, with extremal values saturated by free theories of different matter content. Through confinement, QCD transmutes fermionic matter into scalars, revealing a nontrivial flow between extremal correlators. We reconstruct this flow using perturbative QCD and chiral perturbation theory. The observable is accessible with currently available experimental data.

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arXiv2025

On the extraction of $\alpha_\textit{em}(m_Z^2)$ at Tera-$Z$

The current projected sensitivity on the electromagnetic coupling $\alpha_\textit{em}(m_Z^2)$ represents a bottleneck for the precision electroweak program at FCC-ee. We propose a novel methodology to extract this coupling directly from $Z$-pole data. By comparing the differential distribution of electrons, muons and positrons in the forward region, the approach achieves a projected statistical sensitivity below the $10^{-5}$ level, representing a significant improvement over other methods. We assess the impact of leading parametric uncertainties including that of the top quark mass.

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arXiv2024

One-point correlators of conserved and non-conserved charges in QCD

One-point correlators of conserved charges are argued to be perturbatively IR safe in QCD, which includes not only the density of energy, but also those of electric charge, isospin and baryon number. Theoretical and phenomenological aspects of the density matrix of one-point correlators are discussed in the context of the states produced by a chiral current, as in the decay of a polarized electroweak boson. Densities of some non-conserved charges such as energy with arbitrary non-negative powers, despite their incalculability, are shown to obey an infinite set of consistency constraints. QCD is observed to live near a kink in the allowed parameter space of one-point correlators.

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arXiv2024

Recursion for Wilson-line Form Factors

Matrix elements of Wilson-line dressed operators play a central role in the factorization of soft and collinear modes in gauge theories. When expressed using spinor helicity variables, these so-called form factors admit a classification starting from a Maximally Helicity Violating configuration, in close analogy with gauge theory amplitudes. We show that a single-line complex momentum shift can be used to derive recursion relations that efficiently compute these helicity form factors at tree-level: a combination of lower point form factors and on-shell amplitudes serve as the input building blocks. We obtain novel compact expressions for the $1\to 2$ and $1\to 3$ splitting functions in QCD, which also serves to validate our methods.

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arXiv2023

Boundaries of Universal Theories

Universal theories are a broad class of well-motivated microscopic dynamics of the electroweak sector that go beyond the Standard Model description. The long distance physics is described by electroweak parameters which correspond to local operators in the Effective Field Theory. We show how unitarity and analyticity constrain the space of parameters. In particular, the $W$ and $Y$ parameters are constrained to be positive and are necessarily the leading terms in the low energy expansion. We assess the impact of unitarity on the interpretation of Drell-Yan data. In passing, we uncover an unexpected Wilson coefficient transcendental cancellation at the $\mathcal{O}(<10^{-3})$ level.

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arXiv2022

Full Unitarity and the Moments of Scattering Amplitudes

We study the impact of full unitarity on the moment structure of forward scattering amplitudes. We introduce the semiarcs, calculable quantities in the EFT dispersively related to both real and imaginary parts of the UV amplitude for a fixed number of subtractions. It is observed that large hierarchies between consecutive moments are forbidden by unitarity. Bounds from full unitarity compete with the ones stemming from convexity, and become more important in EFTs where the loop expansion is more important than the derivative expansion.

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arXiv2022

Energy Correlators of Hadronically Decaying Electroweak Bosons

Energy correlators are field-theoretically clean and phenomenologically valuable probes of QCD dynamics. We explore the possibility of using the information encoded in the energy correlators of a hadronically decaying electroweak vector boson in order to extract its full decay density matrix. The kinematics of the one- and two-point energy correlators can indeed discriminate between longitudinal and transverse modes and reveal the interference pattern between different vector polarizations. Such observables improve the sensitivity to microscopic new physics affecting the production rate of the different helicities. We assess the impact on higher dimensional EFT operators in simple scenarios.

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arXiv2021

The IR-Side of Positivity Bounds

We show how calculable IR loop effects impact positivity bounds in Effective Field Theories with causal and unitary UV completions. We identify infrared singularities which appear in dispersion relations at $|t|\lesssim m^2$. In the massless limit, they weaken two-sided bounds based on crossing symmetry, such as the lower bound on the amplitude for Galileon scattering. For amplitudes that are analytic in $s$ even for large negative $t$, i.e. $|t|\gg m^2$, we propose a new simple analytic approach to dispersive bounds, which are instead insensitive to the singularities, and explicitly compute the finite contributions from loops. Finally we show that the singularity do not affect the bounds based on smearing in impact parameter.

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arXiv2021

EFT approach to the electron Electric Dipole Moment at the two-loop level

The ACME collaboration has recently reported a new bound on the electric dipole moment (EDM) of the electron, $|d_e|< 1.1 \times 10^{-29}\, {\rm e\cdot cm}$ at 90$\%$ confidence level, reaching an unprecedented accuracy level. This can translate into new relevant constraints on theories beyond the SM laying at the TeV scale, even when they contribute to the electron EDM at the two-loop level. We use the EFT approach to classify these corrections, presenting the contributions to the anomalous dimension of the CP-violating dipole operators of the electron up to the two-loop level. Selection rules based on helicity and CP play an important role to simplify this analysis. We use this result to provide new bounds on BSM with leptoquarks, extra Higgs, or constraints in sectors of the MSSM and composite Higgs models. The new ACME bound pushes natural theories significantly more into fine-tune territory, unless they have a way to accidentally preserve CP.

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arXiv2021

Positive Moments for Scattering Amplitudes

We find the complete set of conditions satisfied by the forward $2\to2$ scattering amplitude in unitarity and causal theories. These are based on an infinite set of energy dependent quantities -- the arcs -- which are dispersively expressed as moments of a positive measure defined at (arbitrarily) higher energies. We identify optimal finite subsets of constraints, suitable to bound Effective Field Theories (EFTs), at any finite order in the energy expansion. At tree-level arcs are in one-to-one correspondence with Wilson coefficients. We establish under which conditions this approximation applies, identifying seemingly viable EFTs where it never does. In all cases, we discuss the range of validity in both couplings and energy. We also extend our results to the case of small but finite~$t$. A consequence of our study is that EFTs in which the scattering amplitude in some regime grows in energy faster than $E^6$ cannot be UV-completed.

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arXiv2020

EFT anomalous dimensions from the S-matrix

We use the on-shell S-matrix and form factors to compute anomalous dimensions of higher dimension operators in the Standard Model Effective Field Theory. We find that in many instances, these computations are made simple by using the on-shell method. We first compute contributions to anomalous dimensions of operators at dimension-six that arise at one-loop. Then we calculate two-loop anomalous dimensions for which the corresponding one-loop contribution is absent, using this powerful method.

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arXiv2019

Higgs Couplings without the Higgs

The measurement of Higgs couplings constitute an important part of present Standard Model precision tests at colliders. In this article, we show that modifications of Higgs couplings induce energy-growing effects in specific amplitudes involving longitudinally polarized vector bosons, and we initiate a novel program to study these very modifications of Higgs couplings off-shell and at high-energy, rather than on the Higgs resonance. Our analysis suggests that these channels are complementary and, at times, competitive with familiar on-shell measurements; moreover these high-energy probes offer endless opportunities for refinements and improvements.

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arXiv2019

Probing light top partners with CP violation

We investigate CP-violating effects induced by light top partners in composite Higgs theories. We find that sizable contributions to the dipole moments of the light SM quarks and leptons are generically generated at the two-loop level through Barr-Zee-type diagrams. The present constraints on the electron and neutron electric dipole moments translate into bounds on top partner masses of order few TeV and are competitive with the reach of LHC direct searches. Interestingly, we find that CP-violation effects are sensitive to the same operators that control top partner single production. Near-future improvements in the determination of the electron dipole moment will extend the reach on top partner masses beyond the 5 - 10 TeV range.

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arXiv2019

Diboson at the LHC vs LEP

We use the current CMS and ATLAS data for the leptonic $pp \to WW, WZ$ channels to show that diboson production is, for a broad class of flavour models, already competitive with LEP-1 measurements for setting bounds on the dimension six operators parametrising the anomalous couplings between the quarks and the electroweak gauge bosons, at least under the assumption that any new particle is heavier than a few TeV. We also make an estimate of the HL-LHC reach with $3$ ab$^{-1}$. We comment on possible BSM interpretations of the bounds, and show the interplay with other searches for a simplified model with vector triplets. We further study the effect of modified $Z$-quark-quark couplings on the anomalous triple gauge coupling bounds. We find that their impact is already significant and that it could modify the constraints on $δg_{1z}$ and $δκ_γ$ by as much as a factor two at the end of HL-LHC ($λ_γ$ is only marginally affected), requiring a global fit to extract robust bounds. We stress the role of flavour assumptions and study explicitly flavour universal and minimal flavour violation scenarios, illustrating the differences with results obtained for universal theories.

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arXiv2018

Probing Electroweak Phase Transition via Enhanced Di-Higgs Production

We consider a singlet extension of the Standard Model (SM) with a spontaneous $Z_2$ breaking and study the gluon-gluon fusion production of the heavy scalar, with subsequent decay into a pair of SM-like Higgs bosons. We find that an on-shell interference effect can notably enhance the resonant di-Higgs production rate up to 40\%. In addition, consistently taking into account both the on-shell and off-shell interference effects between the heavy scalar and the SM di-Higgs diagrams significantly improves the HL-LHC and HE-LHC reach in this channel. As an example, within an effective field theory analysis in an explicitly $Z_2$ breaking scenario, we further discuss the potential to probe the parameter region compatible with a first order electroweak phase transition. Our analysis is applicable for general potentials of the singlet extension of the SM as well as for more general resonance searches.

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arXiv2017

A global view on the Higgs self-coupling at lepton colliders

We perform a global effective-field-theory analysis to assess the precision on the determination of the Higgs trilinear self-coupling at future lepton colliders. Two main scenarios are considered, depending on whether the center-of-mass energy of the colliders is sufficient or not to access Higgs pair production processes. Low-energy machines allow for ~40% precision on the extraction of the Higgs trilinear coupling through the exploitation of next-to-leading-order effects in single Higgs measurements, provided that runs at both 240/250 GeV and 350 GeV are available with luminosities in the few attobarns range. A global fit, including possible deviations in other SM couplings, is essential in this case to obtain a robust determination of the Higgs self-coupling. High-energy machines can easily achieve a ~20% precision through Higgs pair production processes. In this case, the impact of additional coupling modifications is milder, although not completely negligible.

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