arXiv subjects

Jeffrey Kuntz

Publications and source records attributed to Jeffrey Kuntz.

8 recordsLinked to original sources

arXiv2026

Gravitational Background of Alice-Vortices and R7-Branes

Codimension-two vortex solutions are important solitonic objects in both quantum field theory and gravity. In this paper, we construct a class of codimension-two Alice-vortex solutions in axio-dilaton gravity, in which monodromy around the vortex enacts the axion transformation $C_0 \mapsto -C_0$. In IIB supergravity, this furnishes a class of R7-brane backgrounds of the sort predicted by the Swampland Cobordism Conjecture. Such configurations generically carry an intrinsic dipole moment. We extract additional properties of such branes from scattering probes. These results provide further evidence that the worldvolume theory of an R7-brane is an 8D non-supersymmetric interacting quantum field theory.

hep-th↗

arXiv2025

Unitarity through PT symmetry in Quantum Quadratic Gravity

Theories described by non-Hermitian Hamiltonians are known to possess strictly positive energy eigenvalues and exhibit unitary time evolution if the Hamiltonian is symmetric under discrete parity and time (PT) transformation. In this work, we demonstrate how quantum quadratic gravity, a theory that generally violates unitarity when viewed as a Hermitian quantum field theory, can be complex-deformed into such a PT-symmetric theory with an action that consists of a ghost-less Hermitian free part and non-Hermitian interactions. Paying special attention to the gauge symmetry present in the theory, we quantize in the covariant operator formalism after suggesting how the framework might be extended to the pseudo-Hermitian picture. We find compelling evidence that the resulting quantum theory possesses a unitary inner product and a sensible interpretation of quantum probability, thus avoiding the ghost problem present in the Hermitian formulation of quadratic gravity.

hep-th↗

arXiv2025

Primordial Gravitational Waves in Quadratic Gravity

Quadratic gravity is a fourth-order (in derivatives) theory that can serve as an attractive upgrade to the standard description of gravity provided by General Relativity, thanks to its renormalizability and its built-in description of primordial inflation. We bring quadratic gravity into a second-order form by introducing an auxiliary tensor field and we consider the primordial tensor fluctuations (gravitational waves) in the theory around a Friedmann-Lemaître-Robertson-Walker background. After a canonical quantization of the perturbations, we calculate the tensor power spectrum in quasi de Sitter spacetime. We find that the spectral index $n_t$ and the amplitude $A_t$ of the tensor power spectrum are both suppressed by the factor $(1 + 2{\bf H}^2_*/m_\text{gh}^2)^{-1}$, where ${\bf H}_*$ is the Hubble rate at horizon exit and $m_\text{gh}$ is the mass of the spin-two ghost. This restores the slow-roll consistency condition familiar from single-field inflation models, where the tensor-to-scalar ratio $r$ is equal to $-8n_t$ in the lowest nontrivial order in the slow-roll approximation. We also discuss the well-known issue of the ghost problem in fourth-order theories and how it pertains to the results at hand.

gr-qc↗

arXiv2025

Extra Dimensions Beyond the Horizon

We discuss an extra-dimensional braneworld with a 5th dimension compactified on a circle. As a characteristic feature, the warp factor is hyperbolic and separates the hidden and visible branes by a bulk horizon without a singularity. The two most widely separated scales of 4D physics - the 4D Planck mass and 4D cosmological constant - are determined by two physical scales in the extra dimension, namely: $(i)$ the proper size of the extra dimension, $R$, and, $(ii)$ the distance between the visible brane and the horizon, $R_0$. A realistic scale hierarchy between 4D Planck mass and 4D cosmological constant is obtained for $R/R_0\sim2.34$. The usual fine tuning is not reduced but promoted to a fine tuning of two separate brane energy densities that must approach the fundamental scale of the model with very high precision. Our scenario is based on an exact solution to the 5D Einstein equations with a strictly empty bulk and Friedmann-Lemaître-Robertson-Walker metric on the 4D branes. This requires positive 4D brane energy densities and describes an adiabatic runaway solution in agreement with the de Sitter swampland conjecture. The Kaluza-Klein (KK) graviton states are solutions of a modified Pöschl-Teller potential which permits a discrete graviton spectrum of exactly two modes. In addition to the usual massless graviton, our scenario predicts an extra massive spin-2 graviton with a mass gap of $m_1=\sqrt{2}H_0\approx2\times10^{-33}\,\mathrm{eV}$ which might be detectable in the foreseeable future. A KK tower of gravitons, or a possible continuum of massive graviton states, is prohibited by unitarity with respect to the horizon. We discuss hurdles in turning this model into a realistic cosmology at all times, which points us towards 4D brane tensions that that must be raising towards the fundamental scale of the model, while the observable 4D expansion rate is decreasing.

hep-ph↗

arXiv2022

Inflation with Massive Spin-2 Ghosts

We consider a generic model of quadratic gravity coupled to a single scalar and investigate the effects of gravitational degrees of freedom on inflationary parameters. We find that quantum corrections arising from the massive spin-2 ghost generate significant contributions to the effective inflationary potential and allow for a realization of the spontaneous breakdown of global scale invariance without the need for additional scalar fields. We compute inflationary parameters, compare the resulting predictions to well-known inflationary models, and find that they fit well within the Planck and BICEP/Keck collaboration's constraints on inflation.

astro-ph.CO↗

arXiv2022

Spontaneous Conformal Symmetry Breaking and Quantum Quadratic Gravity

We investigate several quantum phenomena related to quadratic gravity after rewriting the general fourth-order action in a more convenient form that is second-order in derivatives and produces only first-class constraints in phase space. We find that a Higgs mechanism may occur in the conformally invariant subset of the general quadratic action if the theory is conformally coupled to a scalar field that acquires a non-zero vacuum expectation value and spontaneously breaks the conformal symmetry. Then, in the broken phase, the originally massless spin-2 ghost may absorb both the scalar and vector fields to become massive. We also perform a BRST quantization of second-order quadratic gravity in the covariant operator formalism and discuss conditions under which unitarity of the full interacting quantum theory may be established.

hep-th↗

arXiv2022

Analysis of Unitarity in Conformal Quantum Gravity

We perform a canonical quantization of Weyl's conformal gravity by means of the covariant operator formalism and investigate the unitarity of the resulting quantum theory. After reducing the originally fourth order theory to second order in time derivatives via the introduction of an auxiliary tensor field, we identify the full Fock space of quantum states under a BRST construction that includes Faddeev-Popov ghost fields corresponding to Weyl transformations. Using the Kugo-Ojima quartet mechanism, we identify the physical subspace of quantum states and find that the subspace containing the transverse spin-2 states comes equipped with an indefinite inner product metric and a one-particle Hamiltonian that possesses only a single eigenstate. We construct the LSZ reduction formula for the S-matrix in this spin-2 subspace and find that unitarity is violated in scattering events. The explicit way in which this violation occurs represents a new view on the ghost-problem in quadratic theories of quantum gravity.

hep-th↗

arXiv2021

Unified Emergence of Energy Scales and Cosmic Inflation

In the quest for unification of the Standard Model with gravity, classical scale invariance can be utilized to dynamically generate the Planck mass $M_\mathrm{Pl}$. Then, the relation of Planck scale physics to the scale of electroweak symmetry breaking $μ_H$ requires further explanation. In this paper, we propose a model that uses the spontaneous breaking of scale invariance in the scalar sector as a unified origin for dynamical generation of both scales. Using the Gildener-Weinberg approximation, only one scalar acquires a vacuum expectation value of $v_S \sim (10^{16-17})\,\mathrm{GeV}$, thus radiatively generating $M_\mathrm{Pl} \approx β_S^{1/2} v_S$ and $μ_H$ via the neutrino option with right handed neutrino masses $m_N = y_M v_S \sim 10^7 \,\mathrm{GeV}$. Consequently, active SM neutrinos are given a mass with the inclusion of a type-I seesaw mechanism. Furthermore, we adopt an unbroken $Z_2$ symmetry and a $Z_2$-odd set of right-handed Majorana neutrinos $χ$ that do not take part in the neutrino option and are able to produce the correct dark matter relic abundance (dominantly) via inflaton decay. The model also describes cosmic inflation and the inflationary CMB observables are predicted to interpolate between those of $R^2$ and linear chaotic inflationary model and are thus well within the strongest experimental constraints.

hep-ph↗