arXiv subjects

Claudio Andrea Manzari

Publications and source records attributed to Claudio Andrea Manzari.

At least 19 recordsLinked to original sources

arXiv2026

The Very Nearly Right Theory of Flavor

A striking empirical observation about the CKM matrix is that the angles of the unitarity triangle $(α, β, γ)$ are very close to $(π/2, π/8, 3 π/8) $, simple fractions of $π$ that are suggestive of an underlying theory linking flavor and spontaneous CP violation. However, relating this empirical observation to an underlying theory of flavor is challenging, since the unitarity triangle is a complicated function of the Yukawa matrices. In this letter we present a simple picture for the Yukawas where this direct link is possible. We begin by parametrizing the ten-dimensional space of flavor data via "nine-link textures", full-rank $Y_{u,d}$ matrices with a total of nine non-zero entries, with a single CP violating phase. Fitting the ten parameters of all such textures to the flavor data reveals a wonderful surprise: the CP phases cluster tightly around multiples of $π/8$! This happens because the entries of $Y_{u,d}$ naturally define a "Yukawa triangle", in most cases identical to the unitarity triangle at leading order in small flavor parameters. Most interestingly, these two triangles are not the same beyond leading order, yielding precise predictions for $(α, β, γ)$ with calculable deviation from $(π/2, π/8, 3 π/8)$, which can be decisively excluded or strongly confirmed by the next generation of experimental measurements of the angles. The 9-link textures are sparse and their determinants are naturally real, which taken together with spontaneous CP violation can resolve the strong CP problem.

hep-ph↗

arXiv2026

Searches for GeV-Scale ALPs at RHIC

We point out that ultra-peripheral Au+Au collision data collected at the Relativistic Heavy Ion Collider, operational during 2000-2026, can be used to search for axion-like particles coupled to photons via the resonant process $γγ\to a \to γγ$. Exploiting the $Z^4$ enhancement of the two-photon luminosity in heavy-ion collisions and the low photon energy thresholds achievable at RHIC, we simulate signal and background processes, the latter dominated by light-by-light scattering, hadronic resonance production, and misidentified $e^+e^-$ pairs, and estimate upper limits on the ALP-photon coupling $g_{aγγ}$ assuming $1.9~\text{nb}^{-1}$ of existing data collected by the PHENIX experiment. We find sensitivity to ALP masses in the range $2~\text{GeV} \lesssim m_a \lesssim 5~\text{GeV}$ with couplings $g_{aγγ} \gtrsim 4\times 10^{-4}~\text{GeV}^{-1}$, probing previously unexplored regions of parameter space. Access to larger luminosity datasets could substantially extend the sensitivity of this search, motivating a dedicated analysis of ultra-peripheral collision data collected at RHIC by PHENIX as well as other experiments.

hep-ph↗

arXiv2026

Generating the fermion mass hierarchy at the TeV scale

We propose a class of theories to generate quark and lepton mass matrices where the scale of new physics is at the TeV scale, without inducing the large flavor and CP violating processes that are often thought to relegate the origin of flavor to energies above $\sim 100$ TeV. The models have new vector-like leptons and quarks, with mass mixings to each other and Yukawa couplings to light Standard Model fields encoded in "chains" reminiscent of dimensional deconstruction. Locality in the chains both generates the hierarchical Standard Model Yukawa matrices, and ensures that CP and flavor violating effects are small, even with the vector-like particles at the TeV scale. A simple extension also generates neutrino masses, whose tiny size is parametrically related to the square of the electron Yukawa coupling. We outline the essential features of these models, explain how fermion mass hierarchies and mixing angles emerge, and explore their phenomenological implications. This framework can be tested both in the final run of the LHC as well as at possible future colliders operating at the 10 TeV scale, and we identify some of the distinctive experimental signatures associated with the production and decay of the new vector-like fermions.

hep-ph↗

arXiv2025

Clearing up the Strong $CP$ problem

The absence of a neutron electric dipole moment (EDM) constrains the quantum chromodynamics (QCD) theta angle to be less than one part in ten billion, posing the Strong $CP$ problem. We revisit two classes of proposed solutions. First, we show that when $P$ or $CP$ is realized as a gauged discrete symmetry - as can arise in quantum gravity - the vacuum necessarily preserves $CP$, contrary to recent claims that discrete-symmetry solutions fail. Gauged discrete models face model-building challenges, such as avoiding contributions to the neutron EDM after spontaneous $P$ or $CP$ breaking, but in principle have no fundamental obstructions. Second, we critically examine recent arguments that the Strong $CP$ problem is illusory, demonstrating that a nonzero neutron EDM at finite $\barθ$ follows directly from well-understood QCD dynamics. Taken together, our results reinforce the reality of the Strong $CP$ problem and highlight gauged discrete-symmetry realizations of $P$ or $CP$ as plausible solutions.

hep-ph↗

arXiv2025

Supernova axions convert to gamma-rays in magnetic fields of progenitor stars

It has long been established that axions could have been produced within the nascent proto-neutron-star formed following the type II supernova SN1987A, escaped the star due to their weak interactions, and then converted to gamma-rays in the Galactic magnetic fields; the non-observation of a gamma-ray flash coincident with the neutrino burst leads to strong constraints on the axion-photon coupling for axion masses $m_a \lesssim 10^{-10}$ eV. In this work we use SN1987A to constrain higher mass axions, all the way to $m_a \sim 10^{-3}$ eV, by accounting for axion production from the Primakoff process, nucleon bremsstrahlung, and pion conversion along with axion-photon conversion on the still-intact magnetic fields of the progenitor star. Moreover, we show that gamma-ray observations of the next Galactic supernova, leveraging the magnetic fields of the progenitor star, could detect quantum chromodynamics axions for masses above roughly 50 $μ$eV, depending on the supernova. We propose a new full-sky gamma-ray satellite constellation that we call the GALactic AXion Instrument for Supernova (GALAXIS) to search for such future signals along with related signals from extragalactic neutron star mergers.

hep-ph↗

arXiv2025

The SN 1987A Cooling Bound on Dark Matter Absorption in Electron Targets

We present new supernova (SN 1987A) cooling bounds on sub-MeV fermionic dark matter with effective couplings to electrons. These bounds probe the parameter space relevant for direct detection experiments in which dark matter can be absorbed by the target material, showing strong complementarity with indirect searches and constraints from dark matter overproduction. Crucially, our limits exclude the projected sensitivity regions of current and upcoming direct detection experiments. Since these conclusions are a priori not valid for light mediators, we extend our analysis to this case. We show that sub-GeV mediators can be produced resonantly both in supernova cores and in the early Universe, altering the SN 1987A analysis for effective couplings. Still, a combination of supernova cooling constraints and limits from dark matter overproduction excludes the entire parameter space relevant for direct detection in this case.

hep-ph↗

arXiv2025

Resonant Landau-Zener Conversion In Multi-Axion Systems

Multiple axions may emerge in the low-energy effective theory of Nature. Generically, the potentials describing these axion fields are non-diagonal, leading to mass mixing between axion states which can be temperature-dependent due to QCD instanton effects. As the temperature of the Universe drops, level crossing can occur, causing resonant conversion between axion states. In this work, we present an analytic study of the cosmological evolution of multi-axion systems including adiabatic and non-adiabatic resonant conversion from one axion state into another during the misalignment process. We show how the Landau-Zener formalism accurately captures the non-adiabatic resonant conversion, permitting an analytic description of the relic abundances of each axion field for nearly any arbitrary two-state axion mass matrix. As an application, we study the mixing of a QCD axion with an axion-like-particle for specific potentials to identify the predictions for haloscope experiments. We conclude that the detection of an axion off the expected QCD mass-coupling line predicts other haloscope targets if it mixes with the QCD axion.

hep-ph↗

arXiv2025

Strong CP and Flavor in Multi-Higgs Theories

We introduce a class of multi-Higgs doublet extensions of the Standard Model that solves the strong CP problem with profound consequences for the flavor sector. The Yukawa matrices are constrained to have many zero entries by a "Higgs-Flavor" symmetry, $G_{\rm HF}$, that acts on Higgs and quark fields. The violation of both CP and $G_{\rm HF}$ occurs in the Higgs mass matrix so that, for certain choices of $G_{\rm HF}$ charges, the strong CP parameter $\barθ$ is zero at tree-level. Radiative corrections to $\barθ$ are computed in this class of theories. They vanish in realistic two-Higgs doublet models with $G_{\rm HF} = \mathbb{Z}_3$. We also construct realistic three-Higgs models with $G_{\rm HF} = \rm U(1)$, where the one-loop results for $\barθ$ are model-dependent. Requiring $\barθ< 10^{-10}$ has important implications for the flavor problem by constraining the Yukawa coupling and Higgs mass matrices. Contributions to $\barθ$ from higher-dimension operators are computed at 1-loop and can also be sufficiently small, although the hierarchy problem of this class of theories is worse than in the Standard Model.

hep-ph↗

arXiv2025

Two Higgs Doublet Solutions to the Strong CP Problem

We solve the strong CP problem in a broad class of two Higgs doublet theories that will be probed at the Large Hadron Collider and at future colliders. These theories feature CP and Abelian flavor symmetries, both broken softly in the scalar potential, that yield realistic quark masses and mixings. The flavor symmetry charges are chosen so that $\barθ=0$ at tree level for all values of the Yukawa and quartic couplings of the theory. We prove that in all such theories the 1-loop contribution to $\barθ$ also vanishes, independently of the mass scale of the second Higgs doublet. We study two illustrative models with flavor group $\mathbb{Z}_3$. The direct contributions to the neutron electric dipole moment are negligible in both models. While the 2-loop contribution to $\barθ$ is less than $10^{-12}$ in one model, it can be as large as $10^{-10}$ in the other, yielding the prospect of a signal in planned experiments. Even with Abelian flavor symmetries, CP violation in neutral kaon mixing is generally expected to yield naturalness bounds on the masses of additional Higgs doublets of order 20 TeV. We prove that for all models in our class, where the flavor symmetry forces $\barθ$ to vanish at tree-level, the flavor-changing neutral currents are CP-conserving, yielding model-dependent bounds from neutral meson mixing near 1 TeV. Mixing of the two CP-even scalars gives corrections to the couplings of the 125 GeV Higgs state to $\bar{t}t, \bar{b}b, \bar{c}c, \barττ$ and $\barμ μ$, giving possible signals at high luminosity runs at LHC and at future colliders. Furthermore, distinctive correlations between corrections in the various channels can probe the underlying flavor symmetry.

hep-ph↗

arXiv2025

On-shell recursion and holomorphic HQET for heavy quark hadronic resonances

We develop a new theoretical framework for the treatment of heavy quark (HQ) resonances within heavy quark effective theory (HQET). This framework uses on-shell recursion techniques to express the resonant amplitude as a product of on-shell subamplitudes, which allows one to employ a form-factor representation of the hadronic matrix elements and to obtain an HQ expansion, but at the price of introducing complex momenta. We construct a generalized ``holomorphic HQET'' onto which such complex-momentum matrix elements can be matched, and we show that $PT$ symmetry ensures the Isgur-Wise functions (and the perturbative corrections) become holomorphic functions of the complex recoil parameter with real coefficients. They are thus an analytic continuation of the standard HQET description. This framework admits a HQ hadron (strong decay) width expansion. At second order, we show it is compatible with data for the $B_{1(2)}^{(*)}$ and $D_{1(2)}^{(*)}$ HQ doublets. Taking the $\bar{B} \to (D_1^*(1^-) \to Dπ)lν$ system as an example, we compute the holomorphic HQET expansion to first order, as well as the complex-momentum on-shell subamplitudes. A toy numerical study of the resulting differential rates demonstrates that this framework generates HQ resonance lineshapes with large tails, resembling those seen in data.

hep-ph↗

arXiv2024

Time-delayed gamma-ray signatures of heavy axions from core-collapse supernovae

Heavy axions that couple to both quantum electrodynamics and quantum chromodynamics with masses on the order of MeV - GeV and high-scale decay constants in excess of $\sim$$10^8$ GeV may arise generically in e.g. axiverse constructions. In this work we provide the most sensitive search to-date for the existence of such heavy axions using Fermi-LAT data towards four recent supernovae (SN): Cas A, SN1987A, SN2023ixf, and SN2024ggi. We account for heavy axion production in the proto-neutron-star cores through nuclear and electromagnetic processes and then the subsequent decay of the axions into photons. While previous works have searched for gamma-rays from SN1987A using the Solar Maximum Mission that observed SN1987A during the SN itself, we show that using Fermi Large Area Telescope data provides an approximately five orders of magnitude improvement in flux sensitivity for axions with lifetimes larger than around 10 years. We find no evidence for heavy axions and exclude large regions of previously-unexplored parameter space.

hep-ph↗

arXiv2024

Dark Matter in A Mirror Solution to the Strong CP Problem

We study thermal production of dark matter (DM) in a realization of the minimal models of Ref.~\cite{Bonnefoy:2023afx}, where parity is used to solve the strong CP problem by transforming the entire Standard Model (SM) into a mirror copy. Although the mirror electron $e^{\prime}$ is a good DM candidate, its viability is mired by the presence of the mirror up-quark $u^{\prime}$, whose abundance is intimately related to the $e^{\prime}$ abundance and must be suppressed. This can be achieved through a sequential freeze-in mechanism, where mirror photons are first produced from SM gluons, and then the mirror photons produce $e'$. After computing the details of this double freeze-in, we discuss the allowed parameter space of the model, which lies at the threshold of experimental observations. We find that this origin of $e'$ DM requires a low reheating temperature after inflation and is consistent with the baryon asymmetry arising from leptogenesis, providing mirror neutrinos have a significant degeneracy. Finally, we show that this $e'$ DM is not compatible with Higgs Parity, the simplest scheme with exact parity, unless SM parameters deviate significantly from their central values or the minimal model is extended.

hep-ph↗

arXiv2023

A Colorful Mirror Solution to the Strong CP Problem

We propose theories of a complete mirror world with parity (P) solving the strong CP problem. P exchanges the entire Standard Model (SM) with its mirror copy. We derive bounds on the two new mass scales that arise: $v'$ where parity and mirror electroweak symmetry are spontaneously broken, and $v_3$ where the color groups break to the diagonal strong interactions. The strong CP problem is solved even if $v_3 \ll v^{\prime}$, when heavy coloured states at the scale $v_3$ may be accessible at LHC and future colliders. Furthermore, we argue that the breaking of P introduces negligible contributions to $\bar θ_\text{QCD}$, starting at three-loop order. The symmetry breaking at $v_3$ can be made dynamical, without introducing an additional hierarchy problem.

hep-ph↗

arXiv2023

Supernova Limits on Muonic Dark Forces

Proto-neutron stars formed during core-collapse supernovae are hot and dense environments that contain a sizable population of muons. If these interact with new long-lived particles with masses up to roughly 100 MeV, the latter can be produced and escape from the stellar plasma, causing an excessive energy loss constrained by observations of SN 1987A. In this article we calculate the emission of light dark fermions that are coupled to leptons via a new massive vector boson, and determine the resulting constraints on the general parameter space. We apply these limits to the gauged $L_μ-L_τ$ model with dark fermions, and show that the SN 1987A constraints exclude a significant portion of the parameter space targeted by future experiments. We also extend our analysis to generic effective four-fermion operators that couple dark fermions to muons, electrons, or neutrinos. We find that SN 1987A cooling probes a new-physics scale up to $\sim7$ TeV, which is an order of magnitude larger than current bounds from laboratory experiments.

hep-ph↗

arXiv2023

Consistency and Interpretation of the LHC (Di-)Di-Jet Excesses

ATLAS observed a limit for {the cross section of di-jets resonances, which is weaker than expected for a} mass slightly below $\approx$1\TeV. In addition, CMS reported hints for the (non-resonant) pair production of di-jet resonances $X$ via a particle $Y$ at a very similar mass range with a local (global) significance of 3.6\,$σ$ (2.5\,$σ$) at $m_X\approx950\,$GeV. In this article we show that using the preferred range for $m_X$ from the ATLAS analysis, one can reinterpret the CMS analysis of di-di-jets in terms of a resonant search with $Y\to XX$, with a significantly reduced look-elsewhere effect, finding an excess for $m_Y\!\approx\!3.6$\TeV with a significance of $4.0\,σ$ ($3.2\,σ$) locally (globally). We present two possible UV completions capable of explaining the (di-)di-jet excesses, one containing two scalar di-quarks, the other one involving heavy gluons based on an $SU(3)_1\!\times\! SU(3)_2\!\times\! SU(3)_3$ gauge symmetry, spontaneously broken to $SU(3)$ color. In the latter case, non-perturbative couplings are required, pointing towards a composite or extra-dimensional framework. In fact, using 5D-AdS space-time, one obtains the correct mass ratio for $m_X/m_Y$, assuming the $X$ is the lowest lying resonance, and predicts a third (di-)di-jet resonance with a mass around $\approx2.2$\TeV.

hep-ph↗

arXiv2022

Unified Explanation of the Anomalies in Semi-Leptonic $B$ decays and the $W$ Mass

The discrepancies between the measurements of rare (semi-)leptonic $B$ decays and the corresponding Standard Model predictions point convincingly towards the existence of new physics for which a heavy neutral gauge boson ($Z^\prime$) is a prime candidate. However, the effect of the mixing of the $Z^\prime$ with the SM $Z$, even though it cannot be avoided by any symmetry, is usually assumed to be small and thus neglected in phenomenological analyses. In this letter we point out that a mixing of the naturally expected size leads to lepton flavour universal contributions, providing a very good fit to $B$ data. Furthermore, the global electroweak fit is affected by $Z-Z^\prime$ mixing where the tension in the $W$ mass, recently confirmed and strengthened by the CDF measurement, prefers a non-zero value of it. We find that a $Z^\prime$ boson with a mass between $\approx 1-5\,\rm {TeV}$ can provide a unified explanations of the $B$ anomalies and the $W$ mass. This strongly suggests that the breaking of the new gauge symmetry giving raise to the $Z^\prime$ boson is linked to electroweak symmetry breaking with intriguing consequences for model building.

hep-ph↗

arXiv2022

Comprehensive Analysis of Charged Lepton Flavour Violation in the Symmetry Protected Type-I Seesaw

The type-I seesaw model is probably the most straightforward and best studied extension of the Standard Model that can account for the tiny active neutrino masses determined from neutrino oscillation data. In this article, we calculate the complete set of one-loop corrections to charged lepton flavour violating processes within this model. We give the results both using exact diagonalisation of the neutrino mass matrix, and at at leading order in the seesaw expansion (i.e. $\mathcal{O}(v^2/M_R^2)$). Furthermore, we perform the matching onto the $SU(2)_L$ invariant Standard Model Effective Field Theory at the dimension-6 level. These results can be used as initial conditions for the renormalisation group evolution from the right-handed neutrino scale down to the scale of the physical processes, which resums large logarithms. In our numerical analysis, we study the inverse seesaw limit, i.e. the symmetry protected type-I seesaw, where the Wilson coefficient of the Weinberg operator is zero such that sizeable neutrino Yukawas are permissible and relevant effects in charged lepton flavour violating observables are possible. We correlate the different charged lepton flavour violating processes, e.g. $\ell\to\ell^\primeγ$, $\ell\to3\ell^\prime$, $μ\to e$ conversion and $Z\to \ell\ell^\prime$, taking into account the constraints from electroweak precision observables and tests of lepton flavour universality.

hep-ph↗

arXiv2022

A Flavour Inspired Model for Dark Matter

The discrepancies between data on rare $b$-hadron decays, controlled by the underlying neutral-current transitions $b\to s\ell^+\ell^- (\ell = e, μ)$, and the corresponding Standard Model predictions constitute one of the most intriguing hints for new physics. Leptoquarks are prime candidates to solve these anomalies and, in particular, the scalar leptoquark, $S_3$, triplet under $SU(2)_L$ with hypercharge $Y=-1/3$, provides a very good fit to data. Here, for the first time, we entertain the possibility that the same scalar leptoquark, responsible for the LFU anomalies, is the portal to a dark sector consisting of two additional vector-like fermions, one of which is a candidate for the cosmological dark matter. We study two scenarios, where the dark matter candidate belongs to an $SU(2)_L$ singlet and triplet respectively, and discuss the theory parameter space in the context of the dark matter candidate's relic density and prospects for direct and indirect dark matter searches. Direct detection rates are highly suppressed, and generically below the neutrino floor. Current observations with, and future prospects for, high-energy gamma-ray telescopes such as HESS and the Cherenkov Telescope Array are much more promising, as they already provide powerful constraints on the models under consideration, and will potentially probe the full parameter space in the future.

hep-ph↗