arXiv subjects

Gia Dvali

Publications and source records attributed to Gia Dvali.

At least 37 records · Page 2Linked to original sources

arXiv2024

Coherent States in Gauge Theories: Topological Defects and Other Classical Configurations

We present a formulation of coherent states as of consistent quantum description of classical configurations in the BRST-invariant quantization of electrodynamics. The quantization with proper gauge-fixing is performed on the vacuum of the theory, whereas other backgrounds are obtained as BRST-invariant coherent states. One of the key insights is the possibility of constructing the coherent states of pure-gauge configurations. This provides a coherent state understanding of topologically non-trivial configurations in gauge theories, and makes number of features, such as the suppression of transitions between topologically-distinct sectors, very transparent at full quantum level. As an example, we construct the Nielsen-Olesen string as a BRST-invariant coherent state. The Abelian pure-gauge configurations can also be viewed as useful analogs for a set of space-times related by coordinate reparameterizations in General Relativity.

hep-th↗

arXiv2024

Consistent Canonical Quantization of Gravity: Recovery of Classical GR from BRST-invariant Coherent States

We perform canonical quantization of General Relativity, as an effective quantum field theory below the Planck scale, within the BRST-invariant framework. We show that the promotion of constraints to dynamical equations of motion for auxiliary fields leads to the healthy Hamiltonian flow. In particular, we show that the classical properties of Einstein's gravity, such as vanishing Hamiltonian modulo boundary contribution, is realized merely as an expectation value in appropriate physical states. Most importantly, the physicality is shown not to entail trivial time-evolution for correlation functions. In the present approach we quantize the theory once and for all around the Minkowaski vacuum and treat other would-be classical backgrounds as BRST-invariant coherent states. This is especially important for cosmological spacetimes as it uncovers features that are not visible in ordinary semi-classical treatment. The Poincaré invariance of the vacuum, essential for our quantization, provides strong motivation for spontaneously-broken supersymmetry.

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arXiv2024

A String Theoretic Derivation of Gibbons-Hawking Entropy

We describe an attempt of string theoretic derivation of the Gibbons-Hawking entropy. Despite not admitting a de Sitter vacuum, the string theory, by the power of open-close correspondence, captures the Gibbons-Hawking entropy as the entropy of Chan-Paton species on a de Sitter-like state obtained via $D$-branes. Moreover, this derivation sheds a new light at the origin of the area-form, since the equality takes place for a critical 't Hooft coupling for which the species entropy of open strings saturates the area-law unitarity bound.

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arXiv2024

Hint to Supersymmetry from GR Vacuum

The $S$-matrix formulation of gravity suggests that the $θ$-vacuum structure must not be sustained by the theory. We point out that, when applied to the vacuum of general relativity, this criterion hints to supersymmetry. The topological susceptibility of gravitational vacuum induced by Eguchi-Hanson instantons can be eliminated neither by spin-$1/2$ fermions nor by an axion coupled via them since such fermions do not provide instanton zero modes. Instead, the job is done by a spin-$3/2$ fermion, hence realizing a local supersymmetry. This scenario also necessitates the spontaneous breaking of supersymmetry and predicts the existence of axion of $R$-symmetry which gets mass exclusively from the gravitational instantons. The $R$-axion can be a viable dark matter candidate. Matching between the index and the anomaly imposes a constraint that spin-$1/2$ fermions should not contribute to the chiral gravitational anomaly.

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arXiv2024

Memory Burden Effect in Black Holes and Solitons: Implications for PBH

The essence of the \textit{memory burden} effect is that a load of information carried by a system stabilizes it. This universal effect is especially prominent in systems with a high capacity of information storage, such as black holes and other objects with maximal microstate degeneracy, the entities universally referred to as \textit{saturons}. The phenomenon has several implications. The memory burden effect suppresses a further decay of a black hole, the latest, after it has emitted about half of its initial mass. As a consequence, the light primordial black holes (PBHs), that previously were assumed to be fully evaporated, are expected to be present as viable dark matter candidates. In the present paper, we deepen the understanding of the memory burden effect. We first identify various memory burden regimes in generic Hamiltonian systems and then establish a precise correspondence in solitons and in black holes. We make transparent, at a microscopic level, the fundamental differences between the stabilization by a quantum memory burden versus the stabilization by a long-range classical hair due to a spin or an electric charge. We identify certain new features of potential observational interest, such as the model-independent spread of the stabilized masses of initially degenerate PBHs.

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arXiv2024

Vortex Effects in Merging Black Holes and Saturons

Vorticity has recently been suggested to be a property of highly-spinning black holes. The connection between vorticity and limiting spin represents a universal feature shared by objects of maximal microstate entropy, so-called saturons. Using $Q$-ball-like saturons as a laboratory for black holes, we study the collision of two such objects and find that vorticity can have a large impact on the emitted radiation as well as on the charge and angular momentum of the final configuration. As black holes belong to the class of saturons, we expect that the formation of vortices can cause similar effects in black hole mergers, leading to macroscopic deviations in gravitational radiation. This could leave unique signatures detectable with upcoming gravitational-wave searches, which can thereby serve as a portal to macroscopic quantum effects in black holes.

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arXiv2024

New Mass Window for Primordial Black Holes as Dark Matter from Memory Burden Effect

The mass ranges allowed for Primordial Black Holes (PBHs) to constitute all of Dark Matter (DM) are broadly constrained. However, these constraints rely on the standard semiclassical approximation which assumes that the evaporation process is self-similar. Quantum effects such as memory burden take the evaporation process out of the semiclassical regime latest by half-decay time. What happens beyond this time is currently not known. However, theoretical evidence based on prototype models indicates that the evaporation slows down thereby extending the lifetime of a black hole. This modifies the mass ranges constrained, in particular, by BBN and CMB spectral distortions. We show that previous constraints are largely relaxed when the PBH lifetime is extended, making it possible for PBHs to constitute all of DM in previously excluded mass ranges. In particular, this is the case for PBHs lighter than $10^9$g which enter the memory burden stage before BBN and are still present today as DM.

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arXiv2023

Kaluza-Klein Spectroscopy from Neutron Oscillations into Hidden Dimensions

Neutrons and neutrinos are natural probes for new physics. Since they carry no conserved gauge quantum numbers, both can easily mix with the fermions from hidden sectors. A particularly interesting effect is the oscillation of a neutron or a neutrino into a fermion propagating in large extra dimensions. In fact, such a mixing has been identified as the possible origin of small neutrino mass. In this paper, we study neutron oscillations into an extra-dimensional fermion and show that this effect provides a resonance imaging of the Kaluza-Klein tower. The remarkable feature of this phenomenon is its generic nature: because of a fine spacing of the Kaluza-Klein tower, neutrons at a variety of energy levels, both free or within nuclei, find a bulk oscillation partner. In particular, the partner can be a Kaluza-Klein mode of the same species that gives mass to the neutrino. The existence of bulk states matching the neutron energy levels of nuclear spectra gives rise to tight constraints as well as to potentially observable effects. For a free neutron, we predict recurrent resonant oscillations occurring with the values of the magnetic field correlated with the KK levels. We derive bounds on extra dimensions from ultra-cold neutron experiments and suggest signatures for refined measurements, which, in particular, can probe the parameter space motivated by the Hierarchy Problem. Ultra-cold neutron experiments offer a unique way of Kaluza-Klein spectroscopy.

hep-ph↗

arXiv2023

Black holes as tools for quantum computing by advanced extraterrestrial civilizations

We explain that black holes are the most efficient capacitors of quantum information. It is thereby expected that all sufficiently advanced civilizations ultimately employ black holes in their quantum computers. The accompanying Hawking radiation is democratic in particle species. Due to this, the alien quantum computers will radiate in ordinary particles such as neutrinos and photons within the range of potential sensitivity of our detectors. This offers a new avenue for SETI, including the civilizations entirely composed of hidden particles species interacting with our world exclusively through gravity.

physics.pop-ph↗

arXiv2023

Confinement Slingshot and Gravitational Waves

In this paper, we introduce and numerically simulate a quantum field theoretic phenomenon called the gauge ``slingshot" effect and study its production of gravitational waves. The effect occurs when a source, such as a magnetic monopole or a quark, crosses the boundary between the Coulomb and confining phases. The corresponding gauge field of the source, either electric or magnetic, gets confined into a flux tube stretching in the form of a string (cosmic or a QCD type) that attaches the source to the domain wall separating the two phases. The string tension accelerates the source towards the wall as sort of a slingshot. The slingshot phenomenon is also exhibited by various sources of other co-dimensionality, such as cosmic strings confined by domain walls or vortices confined by $Z_2$ strings. Apart from the field-theoretic value, the slingshot effect has important cosmological implications, as it provides a distinct source for gravitational waves. The effect is expected to be generic in various extensions of the standard model such as grand unification.

hep-ph↗

arXiv2023

Neutrinoless double beta decay: neutrino mass versus new physics

Neutrinoless double beta decay is the textbook example of lepton number violation, often claimed to be a probe of neutrino Majorana mass. However, it could be triggered by new physics; after all, neutrino Majorana mass requires physics beyond the Standard Model. If at least one electron were right-handed, it would automatically signify new physics rather than neutrino mass. In case both electrons were left-handed, the situation would become rather complicated, and additional effort would be needed to untangle the source for this process. We offer a comprehensive study of this issue from both the effective operator approach and the possible UV completions, including the Pati-Salam quark-lepton unification. While neutrino exchange is natural and physically preferred, our findings show that new physics can still be responsible for the neutrinoless double beta decay. In particular, the Pati-Salam theory can do the job, consistently with all the phenomenological and unification constraints, as long as the unification scale lies above 10^12 GeV, albeit at the price of fine-tuning of some scalar masses.

hep-ph↗

arXiv2023

Time- and Space-Varying Neutrino Mass Matrix from Soft Topological Defects

We study the formation and evolution of topological defects that arise in the post-recombination phase transition predicted by the gravitational neutrino mass model in [Dvali, Funcke, Phys. Rev. D 93, 113002 (2016)]. In the transition, global skyrmions, monopoles, strings, and domain walls form due to the spontaneous breaking of the neutrino flavor symmetry. These defects are unique in their softness and origin; as they appear at a very low energy scale, they only require Standard Model particle content, and they differ fundamentally depending on the Majorana or Dirac nature of the neutrinos. One of the observational signatures is the time dependence and space dependence of the neutrino mass matrix, which could be observable in future neutrino experiments. Already existing data rule out parts of the parameter space in the Majorana case. The detection of this effect could shed light onto the open question of the Dirac versus Majorana neutrino nature.

hep-ph↗

arXiv2023

Radiation Emission during the Erasure of Magnetic Monopoles

We study the interactions between 't Hooft-Polyakov magnetic monopoles and the domain walls formed by the same order parameter within an $SU(2)$ gauge theory. We observe that the collision leads to the erasure of the magnetic monopoles, as suggested by Dvali, Liu, and Vachaspati. The domain wall represents a layer of vacuum with un-Higgsed $SU(2)$ gauge symmetry. When the monopole enters the wall, it unwinds, and the magnetic charge spreads over the wall. We perform numerical simulations of the collision process and in particular analyze the angular distribution of the emitted electromagnetic radiation. As in the previous studies, we observe that erasure always occurs. Although not forbidden by any conservation laws, the monopole never passes through the wall. This is explained by entropy suppression. The erasure phenomenon has important implications for cosmology, as it sheds a very different light on the monopole abundance in post-inflationary phase transitions and provides potentially observable imprints in the form of electromagnetic and gravitational radiation. The phenomenon also sheds light on fundamental aspects of gauge theories with coexisting phases, such as confining and Higgs phases. Additionally to the figures, the results of the numerical simulations can be found in the following video: https://youtu.be/JZaXUYikQbo

hep-th↗

arXiv2023

Vortices in Black Holes

We argue that black holes admit vortex structure. This is based both on a graviton-condensate description of a black hole as well as on a correspondence between black holes and generic objects with maximal entropy compatible with unitarity, so-called saturons. We show that due to vorticity, a $Q$-ball-type saturon of a calculable renormalizable theory obeys the same extremality bound on the spin as the black hole. Correspondingly, a black hole with extremal spin emerges as a graviton condensate with vorticity. This offers a topological explanation for the stability of extremal black holes against Hawking evaporation. Next, we show that in the presence of mobile charges, the global vortex traps a magnetic flux of the gauge field. This can have macroscopically-observable consequences. For instance, the most powerful jets observed in active galactic nuclei can potentially be accounted for. As a signature, such emissions can occur even without a magnetized accretion disk surrounding the black hole. The flux entrapment can provide an observational window to various hidden sectors, such as millicharged dark matter.

hep-th↗

arXiv2023

Saturon Dark Matter

Saturons are macroscopic objects with maximal microstate entropy. Due to this property, they can be produced via quantum transitions from a homogeneous thermal bath, bypassing the standard exponential suppression characteristic of ordinary extended objects. In this sense, saturons carry an advantage with respect to other macroscopic objects such as black holes and ordinary solitons. Due to unsuppressed thermal production, saturons can have interesting cosmological implications. In particular they can serve as viable dark matter candidates with some unique features. Unlike ordinary particle dark matter, the superheavy saturons can freeze-in at very low temperatures. A nucleation of a saturon can be described in terms of a saturated instanton. This has implications for various phase transitions.

hep-ph↗

arXiv2022

Erasure of Strings and Vortexes

The interaction of defects can lead to a phenomenon of erasure. During this process, a lower-dimensional object gets absorbed and dissolved by a higher-dimensional one. The phenomenon is very general and has a wide range of implications, both cosmological and fundamental. In particular, all types of strings, such as cosmic strings, QCD flux tubes, or fundamental strings, get erased when encountering a defect, either solitonic or a $D$-brane that deconfines their fluxes. This leads to a novel mechanism of cosmic string break-up, accompanied by gravitational and electromagnetic radiations. The arguments based on loss of coherence and the entropy count suggest that the erasure probability is very close to one, and strings never make it through the deconfining layer. We confirm this by a numerical simulation of the system, which effectively captures the essence of the phenomenon: a $2+1$-dimensional problem of interaction between a Nielsen-Olesen vortex of a $U(1)$ Higgs model and a domain wall inside which the $U(1)$ gauge group is unHiggsed and the magnetic flux is deconfined. In accordance with the entropy argument, in our simulation, the vortex never makes it across the wall.

hep-th↗

arXiv2022

Perturbative Understanding of Non-Perturbative Processes and Quantumization versus Classicalization

In some instances of study of quantum evolution of classical backgrounds it is considered inevitable to resort to non-perturbative methods at the price of treating the system semiclassically. We show that a fully quantum perturbative treatment, in which the background is resolved as a multi-particle state, recovers the semiclassical non-perturbative results and allows going beyond. We reproduce particle-creation by a classical field in a theory of two scalars as well as in scalar QED in terms of scattering processes of high multiplicity. The multi-particle treatment also gives a transparent picture of why a single-process transition from a classical to a quantum state, which we call quantumization, is exponentially suppressed, whereas the opposite process, classicalization, can take place swiftly if the microstate degeneracy of the classical state is high. An example is provided by the $N$-graviton portrait of a black hole: a black hole can form efficiently via a $2\to N$ classicalization process in the collision of high-energy particles but its quantumization via a decay $N \to 2$ is exponentially suppressed.

hep-th↗

arXiv2022

Dynamics of Confined Monopoles and Similarities with Confined Quarks

In this work, we study the annihilation of a pair of `t Hooft-Polyakov monopoles due to confinement by a string. We analyze the regime in which the scales of monopoles and strings are comparable. We compute the spectrum of the emitted gravitational waves and find it to agree with the previously calculated point-like case for wavelengths longer than the system width and before the collision. However, we observe that in a head-on collision, monopoles are never re-created. Correspondingly, not even once the string oscillates. Instead, the system decays into waves of Higgs and gauge fields. We explain this phenomenon by the loss of coherence in the annihilation process. Due to this, the entropy suppression makes the recreation of a monopole pair highly improbable. We argue that in a similar regime, analogous behaviour is expected for the heavy quarks connected by a QCD string. There too, instead of re-stretching a long string after the first collapse, the system hadronizes and decays in a high multiplicity of mesons and glueballs. We discuss the implications of our results.

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