arXiv subjects

Giacomo Cacciapaglia

Publications and source records attributed to Giacomo Cacciapaglia.

At least 19 recordsLinked to original sources

arXiv2026

Grand-unification Theory Atlas: Standard Model and Beyond

Under a reasonable set of ab-initio assumptions, we define and chart the atlas of simple gauge theories with families of fermions whose masses are forbidden by gauge invariance. We propose a compass to navigate the atlas based on counting degrees of freedom. When searching for Grand-unification Theories with three matter generations, the free energy singles out the SU(5) Georgi-Glashow model as the minimal one, closely followed by SO(10) with spinorial matter. The atlas also defines the dryland of grand-unifiable gauge extensions of the standard model. We further provide examples relevant for gauge dual completions of the standard model as well as extensions by an additional SU(N) gauge symmetry.

hep-ph↗

arXiv2026

Impact of Higgs precision measurements at the LHC and FCC-ee on the spectrum of composite Higgs models

We investigate the minimal composite Higgs model based on the symmetry-breaking pattern $\mathrm{SU}(4)\rightarrow\mathrm{Sp}(4)$, where electroweak symmetry breaking is governed by the vacuum alignment angle $θ$. Through the leading-order relations $κ_V=\cosθ$ and $m_η=m_h/\sinθ$, precision measurements of Higgs couplings are translated into direct constraints on the vacuum structure and the singlet pseudo-Nambu--Goldstone boson mass. Using the current ATLAS Run-2 measurement of $κ_V$, we construct a Bayesian posterior for $θ$, including the Jacobian associated with the transformation from $κ_V$ to $θ$, and validate the results through an independent frequentist $Δχ^2$ analysis. The same framework is then applied to the projected sensitivities of the High-Luminosity LHC and FCC-ee. The current data imply a conservative lower bound of approximately $440~\mathrm{GeV}$ on the singlet mass at the $95\%$ credibility level, while the projected sensitivities improve this limit to about $600~\mathrm{GeV}$ at the HL-LHC and beyond $2~\mathrm{TeV}$ at FCC-ee. The close agreement between the Bayesian and frequentist determinations demonstrates the robustness of the extracted constraints. These results show that future Higgs precision measurements will probe the vacuum alignment of the minimal $\mathrm{SU}(4)/\mathrm{Sp}(4)$ composite Higgs model with unprecedented sensitivity, placing increasingly stringent constraints on the allowed parameter space and establishing the singlet scalar as a compelling target for upcoming collider programs.

hep-ph↗

arXiv2026

Perusing confining pseudoreal theories: a story of emerging massless spin-1 bosons

Solving quantum field theory, which is at the basis of the standard model of particle interactions, is one of the main tasks of contemporary theoretical physics. Minimal asymptotically free pseudoreal theories, containing one or two species of massless Weyl fermions in pseudoreal representations of the gauge group, flow towards a poorly understood infrared dynamics. We provide a comprehensive study of all pseudoreal theories, identifying the ones that likely flow towards a conformal dynamics, while we show that the remaining ones confine with a non-trivial condensate dynamics. Among the latter, all but one one-species theories feature a massless spin-1 state. Instead, the only confining two-species theory likely features two massless spin-1 states and one Nambu-Goldstone boson. These predictions could be further tested, for instance by use of Lattice simulations, the functional renormalization group, and supersymmetric analogs.

hep-th↗

arXiv2026

When Black Holes Can Wear Pants

We investigate the conditions under which black hole fragmentation, the splitting of a black hole horizon into multiple smaller ones, may occur. The simplest realization is that of a single black hole horizon splitting into two, giving rise to the eponymous pants topology. In classical general relativity, the Bekenstein-Hawking area law forbids such processes for Schwarzschild black holes. For spinning Kerr black holes, purely kinematic analyses impose constraints that prevent fragmentation, even in regimes where entropy considerations might allow it, except possibly in near-extremal cases. We then hunt for scenarios where black holes can wear pants: from the well-known Gregory-Laflamme instability in higher dimensions, to the potential effect of superradiant instabilities in non-axisymmetric radiation trapping, to finally gravitational models that modify the relations between entropy and/or horizon radius and the black hole mass in four dimensions. In all such cases, emission of small fragments can be entropically favored, however its occurrence still depends on the kinematic configuration of the initial state. Our analysis clarifies the theoretical landscape where black holes may fragment, which is particularly relevant for primordial black holes and catastrophic events such as black hole mergers.

gr-qc↗

arXiv2026

Heavy Axion from a Confining Mirror GUT

We propose a new framework for solving the strong CP problem via a heavy axion, using mirror symmetry and grand unification. The mirror GUT sector remains unbroken and dynamically generates a calculable heavy mass scale via confinement without fine tuning. Models in this class feature a heavy axion, whose potential is less sensitive to Planck scale corrections, as well as a rich hidden sector from the confined mirror GUT. The solution to the strong CP problem remains unspoiled by the presence of additional phases in the GUT Yukawas, yet allowing the possibility of electric dipole moments within the reach of future experiments. Our proposal offers new directions in GUT model building, axion phenomenology, dark matter and cosmology.

hep-ph↗

arXiv2026

Completely asymptotically free chiral theories with scalars

We provide the conditions for complete asymptotic freedom for chiral gauge theories including scalars, as motivated by grand unified models. These are generalised Georgi-Glashow and Bars-Yankielowicz theories that feature a scalar field transforming either in the fundamental or in the adjoint of the gauge group. In both scenarios, we consider the addition of multiple chiral fermion families. We systematically analyse the interplay between gauge, Yukawa, and quartic couplings required for all interactions to remain asymptotically free at short distances. We find that for both scalar representations, complete asymptotic free models can be obtained for a specific number of colours and multiplicity of vector-like and chiral families.

hep-th↗

arXiv2026

Composite top partners in exotic colour representations

Composite Higgs models with partial compositeness generically predict coloured fermionic resonances associated with the strong dynamics responsible for electroweak symmetry breaking. While most phenomenological studies have focused on colour-triplet and colour-octet top partners, several UV-complete hypercolour constructions also contain fermionic colour sextets. We present a systematic study of these states in the minimal model classes where they arise, constructing the relevant low-energy interactions and deriving their characteristic decay patterns. The sextets predominantly decay through coloured pseudo-Nambu-Goldstone bosons, leading to top-rich final states, while additional channels with $b$-jets and missing transverse energy can be important. We reinterpret existing ATLAS and CMS searches for high-multiplicity final states to derive the dedicated constraints on these resonances. For the benchmark spectra considered, current LHC data exclude individual sextet components up to masses in the $2-2.5$ TeV regime, with stronger bounds when the full sextet multiplet is included, while conservative extrapolations to the HL-LHC indicate a reach close to $3$ TeV. Our results therefore show that colour-sextet fermions provide a powerful and largely unexplored probe of composite Higgs models with partial compositeness.

hep-ph↗

arXiv2026

Recursive relations from diffeomorphism in the Randall-Sundrum model

Models of gravity in warped extra dimensions enjoy invariance under diffeomorphism. We derive the nonlinear transformation rules for the metric perturbations in the unitary gauge. As an off-shell symmetry, the main consequence of diffeomorphism is a set of recursive relations linking consecutive orders in the field expansion of the effective Lagrangian. The physical consequences are briefly explored for the Randall-Sundrum model with hard branes.

hep-th↗

arXiv2026

Composite Hybrid Inflation : Primordial Black Holes and Stochastic Gravitational Waves

We investigate the production of primordial black holes and gravitational waves in composite hybrid inflation. Starting from an effective chiral Lagrangian with a dilaton and pions, we identify inflation occurring due to the walking dynamics of the theory. A $\mathbb{Z}_2$ symmetry-breaking term in the pion sector induces a shift in the inflaton's trajectory, which leads to a tachyonic instability phase. Curvature perturbations grow exponentially, producing copious primordial black holes and a stochastic gravitational wave background. We show that the primordial black hole mass and the gravitational wave frequency are strongly restricted by the anomalous dimensions of the pion operators, with larger anomalous dimensions giving lighter primordial black holes and higher frequency gravitational waves. In both cases, the associated signatures lie within reach of future gravitational wave observatories.

hep-ph↗

arXiv2026

Electroweak precision tests for asymptotic Grand Unification models

Asymptotic grand unification is an alternative framework to traditional quantitative unification, as the renormalisation flow leads towards an ultra-violet safe fixed point. Phenomenologically, 5-dimensional realisations permit new particles with masses as low as the TeV scale, well below the usual unification scale. We explore the impact of such models on electroweak precision observables, focusing on a minimal SU(5) template for concreteness. We show that current measurements are not sensitive to this class of models. Future colliders, such as CEPC and FCC-ee, can push the 95% limit on the Kaluza-Klein mass up to 2 and 4 TeV, respectively, beyond the direct reach of the LHC programme.

hep-ph↗

arXiv2026

One loop renormalization of 5D gauge-Yukawa theories

The common lore dictates that extra dimensional theories loose predictive power at energies just above the compatification scale, due to the power-law running of bulk coupling. We show that five-dimensional gauge-Yukawa theories can be valid up to arbitrarily high scales, provided: 1) A finite number of terms are required to absorb power-law divergences; 2) All power-law running couplings flow to UV fixed points. By explicitly computing bulk and localized divergences for a gauge-Yukawa theory on $\mathcal{S}^1/\mathbb{Z}_2$, we prove the one-loop renormalization properties of Lagrangians containing only interactions that would be renormalizable in four dimensions. The existence of UV fixed points imposes further constraints on the content of the model. Our results provide a consistency check for the high-energy behavior of any 5D theory, and provide a discrimination between UV consistent models and those that can describe only a handful of Kaluza-Klein modes. Hence, we offer the first concrete step towards an all-order proof of `renormalizability' for gauge-Yukawa theories in five dimensions.

hep-th↗

arXiv2025

The Good Qualities of the Weak Axion

The presence of a topological susceptibility in the electroweak sector of the Standard Model motivates the existence of a good quality weak axion $a_W$, associated with the spontaneous breaking of $B\!+\!L$. Its anomalous couplings and tiny mass, generated from electroweak instantons, render $a_W$ photophobic. We find that the strongest bound on the associated decay constant, $f_W$, stems from a loop-induced coupling to electrons, leading to $f_W \gtrsim 1000$ TeV from stellar cooling. Spontaneous breaking of the abelian ${B\!+\!L}$ symmetry induces proton decay via higher dimensional operators controlled by a new physics scale, $Λ$. Existing Super-Kamiokande limits on these decay channels constrain the new physics scale to be $Λ\gtrsim 10^{12}$ GeV. The characteristic channel $p\to e^+ a_W$ and other possible operators mediating interactions with the Standard Model fields yield signals which are not detectable within the allowed parameter space. Future proton decay searches at the next-generation of neutrino experiments offer the most promising avenues to test the good qualities of the weak axion paradigm.

hep-ph↗

arXiv2025

Unveiling the Quantum Nature of Black Holes: Towards a Proof of Hawking Radiation through Gamma-Ray Observations

Hawking's groundbreaking prediction that black holes emit thermal radiation and ultimately evaporate remains unverified due to the extreme faintness of this radiation for stellar-mass or larger black holes. In this study, we explore a novel observational strategy to search for Hawking radiation from asteroid-mass black hole morsels -- hypothetical small black holes that may form and be ejected during catastrophic events such as binary black hole mergers. These black hole morsels are expected to emit gamma rays in the GeV-TeV range on observable timescales. We analyze data from the Fermi Large Area Telescope coinciding with the well-localized binary black hole merger GW170814, searching for delayed gamma-ray signatures associated with morsel evaporation. While we find no evidence for such emission, we place exclusion limits on morsel masses, ruling out the 4 x 10^8 kg scenario at the 95 percent confidence level for a total emitted mass of one solar mass. We also outline future directions, including the incorporation of late-time evaporation spikes, systematic application across the growing gravitational wave catalog, and the enhanced discovery potential of next-generation facilities such as the Cherenkov Telescope Array Observatory.

astro-ph.HE↗

arXiv2025

Probing Long-Lived Photophobic Axion-Like Particles via Prompt Leptons and Mono-$γ$ at FCC-ee and CEPC

We investigate the potential to probe axion-like particles (ALPs) under the photophobic scenario at the FCC-ee and CEPC at the Z-pole, with $\sqrt{s} = 91.2$ GeV. The signal process is $$ e^+e^- \to Z \to γa,\quad a \to \ell^+ \ell^-, $$ where we consider final states with two prompt leptons and one photon, or only one photon (Mono-$γ$). We estimate the sensitivity to the ALP mass $m_a$ and associated energy scale $Λ$ for $a\toμ^+μ^-$ and $a\toτ^+τ^-$ (with leptonic decays of the $τ$) by use of a XGBoost classifier. For an integrated luminosity of 150 ab$^{-1}$ at the Z-pole, the combined leptonic channel can probe the ALP scale $Λ$ between $10$ to $700$~TeV, depending on the ALP mass. The Mono-$γ$ signal offers a complementary probe, reaching $Λ$ up to $2000$~TeV for masses below $20$~GeV.

hep-ph↗

arXiv2025

Hiding in Plain Sight, the electroweak $η_W$

The presence of a topological susceptibility in the electroweak sector of the Standard Model implies the existence of a pseudoscalar state in the spectrum, $η_W$. We show that, within the Standard Model, no new particle is required to form this state. We identify the $η_W$ state with the CP-odd linear combination of the ground states of hydrogen and antihydrogen atoms.

hep-ph↗

arXiv2025

The Cosmological Constant, Dark Matter and the ElectroWeak Scale meet in the Swampland

The Swampland program, which looks for low energy theories consistent with quantum gravity, has led to the introduction of a dark dimension stemming from the cosmological constant. We show that the same argument leads to the emergence of the electroweak scale, once the dark dimension is realised in a warped background. A second warped extra dimension at the TeV scale is, therefore, postulated, where the long-standing problem of the hierarchy between the electroweak and the Planck scales can be addressed. Furthermore, standard model contributions to the cosmological constant are tamed, together with the gravitational ones. In the emergent holistic picture of gravity and gauge interactions, both Planck and the electroweak scales are emergent from a theory with two fundamental scales: $10^{-2}$ eV and $10^{10}$ GeV, which are of geometric origin and, following the Distance Conjecture, natural. Hence, a bridge is established between the two standard models of particle physics and cosmology.

hep-th↗

arXiv2025

Comment to "The asymptotically-free gauge theories"

The recent paper "The asymptotically-free gauge theories" by Ben Gripaios and Khoi Le Nguyen Nguyen [arXiv:2507.12348] presents a proposed classification of gauge theories valid down to arbitrarily short scales. In this comment, we aim to clarify several points and address some statements that may be misleading. We also provide additional context by discussing relevant prior literature and existing classifications.

hep-th↗

arXiv2025

Looking for Black Hole Morsels in Astrophysical Mergers via Hawking Radiation

Gravitational wave observation has provided numerous insights into the merger of astrophysical black holes. In contrast to other violent events (e.g. supernovae), they are, however, not expected to lead to significant emissions of photons and neutrinos. In this paper we discuss a scenario that would lead to characteristic observable gamma ray bursts, which would provide numerous hints to physics beyond General Relativity. Starting from the hypothesis that micro-black holes (called morsels) are formed during the merger process, we show that it is possible to observe their Hawking radiation, which takes the form of gamma ray bursts of a uniquely characteristic form: with energies in the TeV range, their temporal structure is unlike that stemming from any other astrophysical event. Notably, the time delay from the gravitational wave event is correlated to the mass distribution of the morsels. The integrated mass of the morsels, allowed by the unaccounted merger mass, leads to a Hawking radiation in photons that is above the sensitivity of atmospheric Cherenkov telescopes such as HESS, LHAASO and HAWC, and gamma ray space telescopes, such as Fermi-LAT. This renders the hypothesis of morsel creation experimentally testable, and we provide the first concrete bounds on the total mass of morsels formed in specific events.

astro-ph.HE↗