arXiv subjects

Gia Dvali

Publications and source records attributed to Gia Dvali.

At least 19 recordsLinked to original sources

arXiv2026

GUT Color-Triplet Around the Corner: The Story of an Overlooked Lightness

In traditional approach to the doublet-triplet splitting problem in grand unified theories (GUTs) it is assumed that color-triplet partner of the Higgs doublet must be superheavy in order not to mediate proton decay. However, it has been proposed [1] that the splitting, instead of the mass sector, can occur among the Yukawa couplings. In this scenario the color-triplet emerges as a long-lived $T$-particle with the mass around the TeV scale. This framework provides a direct low-energy window into GUT physics. In the present paper, we study an explicit supersymmetric $SO(10)$ GUT which realizes this mechanism, including effects of gravity-mediated supersymmetry breaking. We show how the shift of the heavy fields, triggered by supersymmetry-breaking, generates a tiny coupling between the $T$-particle and the Standard Model fields and explore the resulting phenomenology. Depending on the order of gravitino mass in which the coupling emerges, the lifetime of the $T$-particle is either around a second or exceeds the age of the Universe. In our analysis, we validate some earlier constraints on (super)gravity vacua imposed by the $S$-matrix: based on the Goldstino Argument, we show that none of the GUT vacua have positive energy densities, whereas the Minkowski vacua are safe against tunneling. We also highlight the role of the species scale cutoff in sensitivity of the low energy observables towards the GUT physics.

hep-ph↗

arXiv2026

Exploring Cosmic Rays from Gravity-Limited Acceleration at Supermassive Black Holes

We show that horizon-scale magnetic fields around supermassive black holes (SMBHs), only limited by gravity, yield a universal, model-independent ceiling on electromagnetic energy density. For rotating SMBHs, this field enables particle acceleration up to $\sim\!10^{27}$\,eV set solely by fundamental constants. We identify a parameter space in accretion rate and magnetic field strength in which quiescent nuclei simultaneously satisfy the transparency conditions for Ultra-High-Energy Cosmic Rays (UHECR) escape and the field requirements for reaching Ultra-High Energies (UHE), naturally complementing photon-rich Active Galactic Nuclei (AGN), which favor neutrino production but suppress UHECR escape. We observe that, when including curvature energy losses, the energy of the primaries scales weakly as $E_{\rm curv}\!\propto\!M^{1/4}$ and allows to achieve UHE across different compositions and SMBHs masses ($10^6$--$10^{10}\,M_\odot$), without requiring extreme spins or super-Eddington accretion. A cross-correlation of the Pierre Auger Observatory (PAO) public data with galaxies hosting reliably measured SMBH masses, separating AGN from quiescent hosts, reveals marginal local excesses ($\lesssim\!2.8σ$) consistent with isotropy after correcting for the look-elsewhere effect. The framework provides a direct link between black-hole physics and the maximum energies of cosmic particles, and defines concrete observational tests for next-generation UHECR datasets.

astro-ph.HE↗

arXiv2026

Detecting Axion-Like Particles With Coiled Optical Fibers I: Silica Fibers

We propose a new approach to axion-like particle (ALP) searches based on long, coiled optical fibers in an external magnetic field. We develop the theoretical framework required to describe photon-ALP conversion in this geometry by incorporating transverse boundary conditions and fiber bending. For solid silica fibers with refractive index considerably larger than unity, we show that the leading signal is a phase shift of the photon, with negligible loss due to ALP production. This setup has the potential to set new constraints in the regime of large ALP mass. We further identify parameter regions in which boundary effects become important, in particular for hollow-core fibers, where signals due to ALPs can be significantly enhanced.

hep-ph↗

arXiv2026

On Time-Evolution in Quantum Gravity

We derive an explicit BRST-exact operator identity for the bulk Hamiltonian in quantum gravity, working within a BRST-invariant quantization of General Relativity, treated as a low-energy effective field theory. We show that, up to a boundary term, the Hamiltonian can be written elegantly as the anticommutator of the BRST charge and the temporal ghost field. This form makes manifest that the Hamiltonian flow acts as a time-reparameterization on the correlation functions of the physical degrees of freedom. We demonstrate that the BRST-exactness of the bulk Hamiltonian does not trivialize the time evolution of gravitational backgrounds or bulk correlators, nor does it trivialize scattering amplitudes.

hep-th↗

arXiv2026

Black Hole Memory Burden and its Signatures in Gravitational Waves from Mergers

Swift memory burden (MB) implies that the information stored in a black hole (BH) can modify its classical dynamics when the BH is perturbed. This influences the gravitational waves (GWs) emitted during BH mergers. In this paper, we investigate how the BH memory load is determined by the features of the collapsing source. We show that the memory load can vastly exceed the information content of its progenitor. An extreme example is a BH formed in a two-particle collision, which exhibits maximal MB. We then derive bounds for BHs formed through stellar collapse and examine the impact of swift MB on BH quasinormal modes, quantifying the MB-induced frequency shift of GWs. These findings imply that GW observations probe the fundamental mechanisms of BH information storage as well as their formation history.

gr-qc↗

arXiv2026

Removing the Cosmological Bound on the Axion Scale via Confinement During Inflation

We implement the scenario of early relaxation of the axion via a high scale confinement within $SU(5)$ grand unified theory and study an epoch of strong QCD in inflationary cosmology. We consider scenarios in which, during inflation, the $SU(5)$ is either entirely or partially in the confining phase. This generates an early potential for the axion and dilutes its energy density removing any cosmological upper bound on the decay constant. We show that a phase of strong QCD can be realized by at least two mechanisms: 1) A direct coupling between the inflaton and the gauge fields and/or 2) by restoration of the $SU(5)$ symmetry during the inflationary epoch. In the latter case, strong coupling is already achieved via the RG running of the $SU(5)$ gauge coupling. We show that the mechanism works for all known realizations of the invisible axion idea: Peccei-Quinn (PQ) type formulations in which the anomalous global symmetry is realized via additional scalars (DFSZ) or heavy fermions (KSVZ) as well as the two-form gauge axion formulation based entirely on the QCD gauge redundancy without any anomalous global symmetry. Even if the expectation value of the PQ scalar vanishes during inflation, the axion is a well defined degree of freedom represented by the phase of the fermion 't Hooft determinant. For the DFSZ case, this phase is composed out of a condensate of the ordinary quarks, amounting to an early universe version of the $η'$-meson. In all considered scenarios, the present day axion can be a viable dark matter candidate for an arbitrarily large value of the decay constant.

hep-ph↗

arXiv2026

Cosmological Implications of the Slingshot Effect: Gravitational Waves, Primordial Black Holes and Dark Matter

In this paper, we explore the implications of the so-called slingshot effect. It represents a rather general phenomenon occurring when a localized source, such as a monopole, quark, or a $D$-brane, crosses a domain wall separating the confined (Higgsed) and unconfined (Coulomb) phases of the crossing source. The crossover is accompanied by a stretched ``string'' of proper co-dimensionality that confines the source to the domain wall. The effect takes place for different setups, such as phase transitions leading to confinement, both electric and magnetic, as well as in string theoretic inflation with $D$-branes. We discuss the role of the phenomenon in sourcing gravitational waves and dark matter in the form of Kaluza-Klein gravitons. We also show that the slingshot effect can lead to the formation of primordial black holes in observationally interesting mass ranges for dark matter and high-energy cosmic rays.

hep-ph↗

arXiv2025

The Role of Microstate Degeneracy in Phase Transitions: Gravitational Waves from Bubble Entanglement

Vacuum bubbles, formed in first order phase transitions, have important implications for cosmology. In particular, they source gravitational waves. Usually, it is assumed that, once bubbles are materialized, their state, further evolution and mergers are well-described classically. This paper will show that this intuition breaks down for bubbles which possess high microstate degeneracy. This is generic when the phase transition breaks spontaneously a symmetry. First, the degeneracy enhances the transition rate. Furthermore, the internal quantum state of the bubbles profoundly affects the classical dynamics of their mergers. A bubble, no matter how macroscopic, is born in a maximally entangled quantum state. This state can be viewed as a symmetric superposition of many different would-be classical bubbles. The inner entanglement is largely maintained up until their mergers. The resulting true quantum dynamics of the merger is macroscopically different from any type of classical mergers. These differences are imprinted as macroscopic features in the resulting classical gravitational waves. In this way, the inner microstate entanglement of merging bubbles provides a qualitatively new source of gravitational waves. This phenomenon is quantified and compared with the swift memory burden effect in black hole mergers.

hep-th↗

arXiv2025

The Strong-$CP$ Problem and its Gauge Axion solution as Evidence for Fundamental Strings

The topological susceptibility of the QCD vacuum provides an understanding of $θ$-vacua as vacua of a Chern-Simons gauge theory. In this way, it gives an immediate proof of the physicality of the boundary $θ$-term. This makes the essence of the strong-$CP$ puzzle very transparent and offers a solution in form of the gauge axion, which has exact quality. This axion represents an intrinsic part of the QCD gauge redundancy without any reference to an anomalous global symmetry. It is a two-form transforming under the QCD gauge symmetry. Due to its pure gauge nature, the gauge axion represents a powerful tool to monitor physics of $θ$-vacua in various regimes. Unlike the ordinary Peccei-Quinn axion, which is UV-completed into a Goldstone phase of a complex scalar and thereby suffers from the quality problem, the gauge axion is UV-completed directly into a fundamental theory of gravity. We study the domain wall and string structure of the gauge axion and show that the strings sourcing it must be a part of this fundamental theory. We thus observe that the absence of the axion quality problem motivates the presence of fundamental strings. This provides a new argument for a connection between the axion and gravity.

hep-th↗

arXiv2025

Visions in Quantum Gravity

To deepen our understanding of Quantum Gravity and its connections with black holes and cosmology, building a common language and exchanging ideas across different approaches is crucial. The Nordita Program "Quantum Gravity: from gravitational effective field theories to ultraviolet complete approaches" created a platform for extensive discussions, aimed at pinpointing both common grounds and sources of disagreements, with the hope of generating ideas and driving progress in the field. This contribution summarizes the twelve topical discussions held during the program and collects individual thoughts of speakers and panelists on the future of the field in light of these discussions.

hep-th↗

arXiv2025

Witten Effect in $3$-Form Description of $θ$-vacua

The $θ$-vacua of a gauge theory admit an equivalent formulation as vacua of a massless Chern-Simons $3$-form, which originate from the topological susceptibility of the vacuum. This formulation provides a framework in which the physical manifestations of the $θ$-angle, which are quantum in origin, can be captured at the level of effective classical equations of motion. Within this framework, we derive the Witten effect, demonstrating that in the background of a massless $3$-form, the magnetic monopole indeed acquires an electric charge proportional to $θ$. This result, in particular, provides evidence that instantons, even when constrained by the Higgs effect, maintain a non-zero topological susceptibility of the vacuum. In addition to the Witten effect, we numerically demonstrate that a magnetic monopole exhibits polarizability when placed in a constant background electric field.

hep-th↗

arXiv2025

Swift Memory Burden in Merging Black Holes: how information load affects black hole's classical dynamics

In this paper we argue that the information load carried by a black hole affects its classical perturbations. We refer to this phenomenon as the ``swift memory burden effect" and show that it is universal for objects of high efficiency of information storage. The effect is expected to have observable manifestations, for example, in mergers of astrophysical black holes in Einstein gravity. The black holes with different information loads, although degenerate in the ground state, respond very differently to perturbations. The strength of the imprint is controlled by the memory burden parameter which measures the fraction of the black hole's memory space occupied by the information load. This represents a new macroscopic quantum characteristics of a black hole. We develop a calculable theoretical framework and derive some master formulas which we then test on explicit models of black holes as well as on solitons of high capacity of information storage. We show that the effect must be significant for the spectroscopy of both astrophysical and primordial black holes and can be potentially probed in gravitational wave experiments. We also provide a proposal for the test of the memory burden phenomenon in a table-top laboratory setting with cold bosons.

hep-th↗

arXiv2025

$η_{\rm w}$-meson from topological properties of the electroweak vacuum

We further scrutinize the evidence for a recently suggested pseudo-scalar particle, the electroweak $η_{\rm w}$-meson. Its existence is demanded by matching the removal of the weak vacuum angle $θ_{\rm w}$ by the anomalous $B+L$ - symmetry with a massive pole in the topological susceptibility of the vacuum. We specifically focus on the possibility of the emergence of $η_{\rm w}$ as a collective excitation of the phase of the condensate of the 't Hooft fermion determinant, generated by the electroweak instantons, which breaks the $B+L$ - symmetry spontaneously. We argue that the generation of the 't Hooft vertex is in one-to-one correspondence with its non-zero vacuum expectation value which is cutoff insensitive. We outline certain puzzles about the nature of the emergent $η_{\rm w}$ which require further investigations.

hep-th↗

arXiv2025

Similarities in the evaporation of saturated solitons and black holes

It has been suggested some time ago that many black hole properties are not specific to gravity, but rather are shared by a large class of objects, the so-called saturons, that saturate the quantum field theoretic upper bound on microstate degeneracy. By now, various aspects of this universality have been understood and demonstrated in a number of explicit examples. In the present paper, we add one more brick to the building by showing that the decay of a simple two-dimensional saturated soliton copies some key aspects of the black hole decay as well as of the information retrieval. In particular, we study the evaporation process of a classically-stable vacuum bubble of a spontaneously broken $SU(N)$-symmetry, coupled to massless fermions. We show that the decay rate as well as the characteristic energy of the emitted quanta are given by the inverse size of the object, in striking similarity with the Hawking evaporation of a black hole. The time-scale of information retrieval also matches the one previously suggested for a black hole by Page. We give the semiclassical derivation of the phenomenon as well as its fully quantum resolution as a decaying coherent state of Goldstone bosons. The universal nature of the effect and its microscopic understanding support the analogous quantum portrait of a black hole as a saturated coherent state of gravitons.

hep-th↗

arXiv2025

Electroweak $η_{\rm w}$ meson

We argue that the Standard Model is accompanied by a new pseudo-scalar degree of freedom, $η_{\rm w}$-meson, which cancels the topological susceptibility of the electroweak vacuum and gets its mass from this effect. The prediction is based on the analyticity properties of the Chern-Simons correlator combined with the basic features of gravity. Depending on the quality level of the $U(1)_{B+L}$-symmetry, $η_{\rm w}$ emerges as a $B+L$ pseudo-Goldstone boson or as a Stückelberg $2$-form of the electroweak gauge redundancy. An intriguing scenario of the first category is the emergence of $η_{\rm w}$ in the form of the phase of a $U(1)_{B+L}$-violating fermion condensate triggered by the instantons, somewhat similar to $η'$-meson in QCD. Regardless of its origin, the presence of $η_{\rm w}$-meson in the theory appears to be a matter of consistency.

hep-th↗

arXiv2025

Cosmic strings and domain walls of the QCD quark condensate with and without a hidden axion

The chiral quark condensate of QCD, which spontaneously breaks the anomalous axial symmetry, gives rise to axionic type global string-wall systems. If a Peccei-Quinn type axion exists in the theory, the axionic strings are in general accompanied by winding of the QCD quark condensate. Depending on the axion model the winding can proceed either in the $η'$ or in the pion direction. This determines the structure of fermionic zero modes and the anomaly inflow which has important astrophysical consequences. We point out that $η'$ and pion string-wall systems exist in pure QCD, independently of the hidden axion. Strikingly, even if a hidden axion exists, the early cosmology can be entirely dominated by string-wall systems formed by the QCD quark condensate. We also discuss their role in the QCD phase transition and in heavy-ion physics.

hep-ph↗

arXiv2025

Transitioning to Memory Burden: Detectable Small Primordial Black Holes as Dark Matter

Mounting theoretical evidence suggests that black holes are subjected to the memory burden effect, implying that after certain time the information stored in them suppresses the decay rate. This effect opens up a new window for small primordial black holes (PBHs) below $10^{15}\,{\rm g}$ as dark matter. We show that the smooth transition from semi-classical evaporation to the memory-burdened phase strongly impacts observational bounds on the abundance of small PBHs. The most stringent constraints come from present-day fluxes of astrophysical particles. Remarkably, currently-transitioning small PBHs are detectable through high-energetic neutrino events.

hep-ph↗

arXiv2025

Implications of Photon Mass: Vortextrap Magnetization of Black Holes

We discuss certain astrophysical implications of the photon mass. It offers a new mechanism of black hole magnetization, described as ``vortextrap magnetization" (VTM), which can generate a near-saturated magnetic field in astrophysical black holes. The extreme magnetic field is provided by a large number of Nielsen-Olesen type vortex lines piercing a black hole. In massive photon scenario the galactic magnetic field is a densely populated forest of overlapping magnetic flux tubes. These get trapped and collected by a black hole over a cosmological time-scale. The VTM mechanism neatly fits supermassive black holes with sizes matching the phenomenologically-acceptable values of the photon mass, and has implications for magnetic-field based particle acceleration. Even in absence of surrounding plasma, the near-saturated magnetic field is expected to result into an intense electromagnetic radiation as well as gravitational waves in black hole mergers. We provide a numerical simulation of the VTM phenomenon in a prototype system.

gr-qc↗