arXiv subjects

Julian Heeck

Publications and source records attributed to Julian Heeck.

At least 19 recordsLinked to original sources

arXiv2026

Effects of the interaction of dark matter and neutron-star matter on extreme and intermediate mass-ratio inspirals

Extreme and intermediate mass-ratio inspirals in a dense dark-matter distribution have the effects of the dark matter imprinted on the orbital dynamics of and the emitted gravitational waves from these systems. Prior work has shown that space-based gravitational-wave detectors can measure the dark-matter-induced effects on the gravitational waves, which would give evidence for the presence of dark matter around the massive black hole. In this earlier work, the dark matter has been assumed to have only gravitational interactions (namely, no dark-matter self-annihilation or interactions between dark matter and ordinary baryonic or leptonic matter). In this article, we investigate the gravitational-wave effects of introducing such interactions of dark matter with itself or with ordinary matter in binaries with a neutron-star secondary. We consider broad classes of dark-matter models that change the distribution of dark matter (spikes or annihilation plateaus) and which permit accretion onto the secondary, as well as an increasing or static mass of the neutron star during the inspiral (in addition to the purely gravitational effect of dynamical friction). We find distinctive gravitational-wave signatures of these interactions and of self-annihilation, which in some of the scenarios could be sufficiently large for space-based detectors to distinguish them using gravitational-wave observations of these systems.

gr-qc↗

arXiv2026

Scalar baryons in neutron stars

Neutron stars have baryon chemical potentials that can exceed the neutron mass, providing favorable conditions to convert neutrons to new particles carrying baryon number, even if those processes are kinematically forbidden in vacuum. We study the effect of GeV-scale scalars with baryon number on neutron stars' equation of state and show that non-perturbatively large repulsive self-couplings are required to support the observed two-solar-mass neutron stars. We also study potentials with attractive self-interactions, which can trigger scalar production even for masses above the chemical potential and resemble Coleman's Q-matter.

hep-ph↗

arXiv2026

Basis for non-derivative baryon-number-violating operators

We present a minimal basis for non-derivative baryon-number-violating operators in the Standard Model Effective Field Theory up to mass dimension 11, as well as for the $(\Delta B,\Delta L) = (2,2)$ and $(2,-2)$ operators at dimension 12. Compared to existing results, our bases generally contain fewer terms and simpler contractions, although we also highlight select cases where a minimal basis is incompatible with simple structures.

hep-ph↗

arXiv2026

Gauged Q-balls in flat potentials

Q-balls are large bound-state systems of scalar particles, described classically through localized solutions of the equations of motion. Promoting the required stabilizing U(1) symmetry to a gauge symmetry leads to gauged Q-balls, which cannot grow beyond some maximal size and charge on account of the repulsive gauge interactions. These gauged Q-balls have been studied extensively for scalar potentials that satisfy Coleman's thin-wall criterion; here, we explore gauged Q-balls in flat potentials, which often occur in supersymmetric models. Even though global Q-balls in flat potentials are qualitatively different from Coleman's Q-balls, we find that the gauged versions are remarkably similar. We provide analytic approximations for these solitons and compare to numerical solutions. In addition, we study Proca Q-balls, i.e. make the gauge bosons massive, which interpolates between the global and gauged cases.

hep-ph↗

arXiv2026

Q-balls across dimensions

Scalars carrying a conserved global charge $Q$ can form stable localized field configurations composed of a large number of particles. These non-topological solitons are spherically symmetric and are called Q-balls. While usually analyzed in three spatial dimensions, these solitons can be straightforwardly generalized to $d$ spatial dimensions. For $d=1$, we can analytically solve the non-linear differential equation for an important class of single-field potentials; for $d>1$, we can analytically approximate the solutions in the thin-wall or large Q-ball regime, including the first sub-leading correction consistently. Since the underlying differential equations have the same form as vacuum-decay bounce solutions, our results find applications there, too.

hep-ph↗

arXiv2026

Opening up baryon-number-violating operators

Baryon number violation is our most sensitive probe of physics beyond the Standard Model. Its realization through heavy new particles can be conveniently encoded in higher-dimensional operators that allow for model-agnostic analyses. The unparalleled sensitivity of nuclear decays to baryon number violation makes it possible to probe effective operators of very high mass dimension, far beyond the commonly discussed dimension-six operators. To facilitate studies of this ginormous and scarcely explored testable operator landscape we provide the exhaustive set of tree-level UV completions consisting of scalars, fermions, and vectors for non-derivative baryon-number-violating operators in this Standard Model effective field theory up to mass dimension 15, which corresponds roughly to the border of sensitivity. In addition to the known Standard Model fields we also include right-handed neutrinos in our operators. Our public code can be used to UV-complete any non-derivative operator and match it onto an operator basis.

hep-ph↗

arXiv2025

New avenues for tau flavor violation

I present a concise overview of tau flavor violation and the broad opportunities it offers, with a focus on non-standard decay channels and their underlying theoretical motivations.

hep-ph↗

arXiv2025

Nucleon Decays into Light New Particles in Neutrino Detectors

Proton and neutron decays into light new particles $X$ can drastically change the experimental signatures and benefit from the complementarity of large water-Cherenkov neutrino detectors such as Super/Hyper-Kamiokande and tracking detectors such as JUNO and DUNE. The proton decays $p\to \ell^+ X$ and $p\to \pi^+ X$ with $m_X$ near phase-space closure lead to charged particles below Cherenkov threshold, rendering them practically invisible in Super- and Hyper-Kamiokande but not in JUNO and DUNE, which are therefore uniquely positioned for these baryon-number-violating signatures despite their smaller size. As an additional signature, such nucleon decays in Earth can produce a sizable flux of $X$ particles in underground detectors. We present a simple model in which nucleons decay into sub-GeV sterile neutrinos that subsequently decay through active-sterile neutrino mixing, with a promisingly large number of events in Super-Kamiokande even in the seesaw-motivated parameter space.

hep-ph↗

arXiv2025

Lepton flavor violation by three units

The conservation of lepton flavor is a prediction of the Standard Model and is still an excellent approximate symmetry despite our observation of neutrino oscillations. Lepton flavor violation by one or two units have been discussed for decades, with several dedicated experiments exploring the vast model landscape but no discoveries so far. Here, we explore operators and processes that violate at least one lepton flavor by three units and identify testable signatures. In the Standard Model effective field theory, such operators already arise at mass dimension 7 and can be tested through their contributions to Michel parameters in leptonic decays. True neutrinoless charged-lepton flavor violation arises at mass dimension 10 and can realistically only be seen in the tau decay channels $\tau \to eee\bar{\mu}\bar{\mu}$ or $\tau \to \mu\mu\mu\bar{e}\bar{e}$, for example in Belle II. Testable rates for these tau decays require light new particles and subsequently predict an avalanche of remarkably clean but so-far unconstrained collider signatures.

hep-ph↗

arXiv2025

Revisiting the connection of baryon number, lepton number, and operator dimension

The effects of heavy new particles beyond the Standard Model can be conveniently captured through higher-dimensional effective operators. As noted long ago by Weinberg, the amount of baryon and lepton number an operator can carry is intricately connected to its mass dimension. We derive an improved inequality for this connection and compare it to explicit operator constructions up to mass dimension 25. For the effective field theory of Standard Model plus right-handed neutrinos, our relationship is even an equality up to high mass dimension.

hep-ph↗

arXiv2025

Baryon Number Violation: From Nuclear Matrix Elements to BSM Physics

Processes that violate baryon number, most notably proton decay and $n\bar n$ transitions, are promising probes of physics beyond the Standard Model (BSM) needed to understand the lack of antimatter in the Universe. To interpret current and forthcoming experimental limits, theory input from nuclear matrix elements to UV complete models enters. Thus, an interplay of experiment, effective field theory, lattice QCD, and BSM model building is required to develop strategies to accurately extract information from current and future data and maximize the impact and sensitivity of next-generation experiments. Here, we briefly summarize the main results and discussions from the workshop "INT-25-91W: Baryon Number Violation: From Nuclear Matrix Elements to BSM Physics," held at the Institute for Nuclear Theory, University of Washington, Seattle, WA, January 13-17, 2025.

hep-ph↗

arXiv2025

Decaying scalar dark matter in the minimal left-right symmetric model

In the minimal left-right symmetric theory, the dark matter candidate is usually ascribed to the lightest right-handed neutrino. Here we present an alternative decaying dark matter candidate in this model in terms of the lightest neutral scalar from the $SU(2)_R$-triplet field. This setup requires a vast hierarchy between the scalar mass and the left-right symmetry breaking scale, which renders the scalar dark matter sufficiently stable on cosmological time scales. The stability of the dark matter imposes constraints on the right-handed neutrino mass, which has consequences for the neutrino mass generation, as well as for leptogenesis. Although somewhat fine-tuned, it provides a very economical scenario wherein the minimal left-right model can simultaneously explain dark matter, neutrino masses, and the matter-antimatter asymmetry of the Universe.

hep-ph↗

arXiv2024

Lepton flavor violation with tau leptons

We review the status and importance of lepton flavor violation with tauons, focusing on overlooked flavor-breaking patterns as well as tau-flavor violation in nucleon decays.

hep-ph↗

arXiv2024

Baryon number violation involving tau leptons

Baryon number violation is our most sensitive probe of physics beyond the Standard Model, especially through the study of nucleon decays. Angular momentum conservation requires a lepton in the final state of such decays, kinematically restricted to electrons, muons, or neutrinos. We show that operators involving taus, which are at first sight too heavy to play a role in nucleon decays, still lead to clean nucleon decay channels with tau neutrinos. While many of them are already constrained from existing two-body searches such as $p\to \pi^+\nu$, other operators induce many-body decays such as $p \to \eta \pi^{+} \bar\nu_\tau$ and $n\to K^+ \pi^-\nu_\tau$ that have never been searched for.

hep-ph↗

arXiv2024

Dirac leptogenesis from asymmetry wash-in via scatterings

Leptogenesis typically requires the introduction of heavy particles whose out-of-equilibrium decays are essential for generating a matter-antimatter asymmetry, according to one of Sakharov's conditions. We demonstrate that in Dirac leptogenesis, scatterings between the light degrees of freedom -- Standard Model particles plus Dirac neutrinos - are sufficient to generate the asymmetry. The generation requires at least two effective charges conserved by the fast Standard Model interactions. Due to its vanishing source term in the Boltzmann equations, the asymmetry of right-handed neutrinos solely arises through wash-in processes. Sakharov's conditions are satisfied because the right-handed neutrino partners are out of equilibrium. Consequently, heavy degrees of freedom never needed to be produced in the early universe, allowing for a reheating temperature well below their mass scale. Considering a minimal leptoquark model, we discuss the viable parameter space along with the potential observational signature of an increased number of effective neutrinos in the early universe.

hep-ph↗

arXiv2024

Lepton flavor violation by two units

Charged lepton flavor violation arises in the Standard Model Effective Field Theory at mass dimension six. The operators that induce neutrinoless muon and tauon decays are among the best constrained and are sensitive to new-physics scales up to $10^7\,$GeV. An entirely different class of lepton-flavor-violating operators violates lepton flavors by two units rather than one and does not lead to such clean signatures. Even the well-known case of muonium--anti-muonium conversion that falls into this category is only sensitive to two out of the three $\Delta L_\mu = - \Delta L_e = 2$ dimension-six operators. We derive constraints on many of these operators from lepton flavor universality and show how to make further progress with future searches at Belle II and future experiments such as $Z$ factories or muon colliders.

hep-ph↗

arXiv2023

Neutrino mass models at $\mu$TRISTAN

We study the prospects of probing neutrino mass models at the newly proposed antimuon collider $\mu$TRISTAN, involving $\mu^+e^-$ scattering at $\sqrt{s}= 346$ GeV and $\mu^+\mu^+$ scattering at $\sqrt{s}= 2$ TeV. We show that $\mu$TRISTAN is uniquely sensitive to leptophilic neutral and doubly-charged scalars naturally occurring in various neutrino mass models, such as Zee, Zee-Babu, cocktail, and type-II seesaw models, over a wide range of mass and coupling values, well beyond the current experimental constraints. It also allows for the possibility to correlate the collider signals with neutrino mixing parameters and charged lepton flavor violating observables.

hep-ph↗

arXiv2023

The Tunneling Potential Approach to Q-Balls

Q-balls are bound-state configurations of complex scalars stabilized by a conserved Noether charge Q. They are solutions to a second-order differential equation that is structurally identical to Euclidean vacuum-decay bounce solutions in three dimensions. This enables us to translate the recent tunneling potential approach to Q-balls, which amounts to a reformulation of the problem that can simplify the task of finding approximate and even exact Q-ball solutions.

hep-ph↗