arXiv subjects

Michael Zantedeschi

Publications and source records attributed to Michael Zantedeschi.

27 records · Page 2Linked to original sources

arXiv2023

Grand unification, small vs large representations, hadron colliders and all that

We review minimal realistic grand unified models based on $SU(5)$ and $SO(10)$ gauge groups. The models with small Higgs representations and higher dimensional operators - under the assumption of no cancellations in proton decay amplitudes - predict nearby oases with new light particles. Two of them stand out: real fermion and scalar weak triplets. The former generates dynamically neutrino Majorana mass through the so-called type III seesaw mechanism, while the latter naturally gets a small vacuum expectation value and thus generically modifies $W$-boson mass. On the contrary, the renormalisable versions of these theories fail to determine the particle spectra. In particular, in the renormalisable version of the $SO(10)$ theory the mass of the right-handed gauge boson - normally assumed (and allowed) to lie far in the desert - could be even accessible at the LHC. Last but not least, we show that in the minimal supersymmetric $SU(5)$ theory all the superpartners can lie orders of magnitude above the weak scale, unless one requires strict naturalness. Thus, the so-called split supersymmetry does not imply any light states.

hep-ph↗

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

SO(10): a Case for Hadron Colliders

We study the mass scales in the $SO(10)$ grand unified theory based on the following minimal Higgs representation content: adjoint $45_{\rm H}$, spinor $16_{\rm H}$ and complex vector $10_{\rm H}$, with higher dimensional operators on top of renormalizable interactions. We show that the consistency of the theory requires scalar $W$ and $Z$, scalar quark doublet and scalar gluon to lie below $ 10\, \rm TeV$ energy and potentially accessible even at the LHC. These signatures are intimately connected with the prediction of proton lifetime below $10^{35} {\rm yr}$, to be probed in the new generation of proton decay experiments.

hep-ph↗

arXiv2023

$SU(5)$ grand unification and $W$-boson mass

A realistic extension of the minimal $SU(5)$ theory consisting of the addition of an adjoint fermion is known to predict light real fermion and scalar weak triplets, potentially accessible at the LHC. These particles, in addition to playing a key role in gauge coupling unification, have profound phenomenological implications. The fermion triplet, that through the seesaw mechanism offers a testable origin of neutrino mass, has been already extensively discussed. The scalar triplet develops a vacuum expectation value that modifies the $W$-boson mass. We show that its low-energy effective theory is remarkably predictive: in the leading approximation, all the relevant physical processes involving the scalar triplet depend only on its mass and the deviation from the Standard Model $W$-mass value.

hep-ph↗

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.

hep-th↗

arXiv2021

Primordial Black Holes from Confinement

A mechanism for the formation of primordial black holes is proposed. Here, heavy quarks of a confining gauge theory produced by de Sitter fluctuations are pushed apart by inflation and get confined after horizon re-entry. The large amount of energy stored in the colour flux tubes connecting the quark pair leads to black-hole formation. These are much lighter and can be of higher spin than those produced by standard collapse of horizon-size inflationary overdensities. Other difficulties exhibited by such mechanisms are also avoided. Phenomenological features of the new mechanism are discussed as well as accounting for both the entirety of the dark matter and the supermassive black holes in the galactic centres. Under proper conditions, the mechanism can be realised in a generic confinement theory, including ordinary QCD. We discuss a possible string-theoretic realisation via $D$-branes. Interestingly, for conservative values of the string scale, the produced gravity waves are within the range of recent NANOGrav data. Simple generalisations of the mechanism allow for the existence of a significant scalar component of gravity waves with distinct observational signatures.

hep-ph↗

arXiv2021

On Evolution of Coherent States as Quantum Counterpart of Classical Dynamics

Quantum dynamics of coherent states is studied within quantum field theory using two complementary methods: by organizing the evolution as a Taylor series in elapsed time and by perturbative expansion in coupling within the interaction-picture formalism. One of the important aspects of our analysis consists in utilizing the operators and the vacuum of interacting theory in constructing the states, without invoking asymptotic particles. Focusing on a coherent state describing a spatially homogeneous field configuration, it is demonstrated that both adopted methods successfully account for nonlinear classical dynamics, giving distinguishable quantum effects. In particular, according to the time-expansion analysis the initial field-acceleration, with which the field departs from its initial expectation value, is governed by the tree-level potential with renormalized mass and bare coupling constant. The interaction-picture computation, instead, can be manipulated to give the nonlinear dynamics, determined in terms of renormalized coupling and mass. However, it results in a logarithmic initial-time singularity in the field-acceleration, reminiscent of the similar behaviour encountered within semi-classical formalism, for certain choices of the initial state for fluctuations. Within our coherent-state analysis, the above mentioned peculiarities are artefacts of an expansion: in the first case over infinitesimal time, while in the second case in the coupling constant. Despite this, we show that the evolution obtained within the interaction-picture analysis is valid for extended period of time. Moreover, on top of the desired classical dynamics, it serves us with interesting quantum corrections, previously proposed by Dvali-Gomez-Zell.

hep-th↗

arXiv2021

Background Field Method and Initial-Time Singularity for Coherent States

The background field method is adopted for studying the dynamics of coherent states within an interacting scalar field theory. Focusing on a coherent state that corresponds to the homogeneous condensate, the quantum depletion of the expectation value of the field-operator is demonstrated to be due to the annihilation of the condensate constituents into relativistic quanta. Moreover, due to the fact that the initial field acceleration and energy for the non-squeezed coherent states are determined in terms of bare coupling constant, instead of the renormalized one, the appearance of perturbative singularities is shown to be inevitable. In other words, consistency of these states requires the finiteness of the bare coupling constant, through the resummation.

hep-th↗

arXiv2020

On the viability of Locked Inflation

We review locked inflation and we critically address phenomenological and consistency issues thathave appeared in the literature. A natural window of opportunity is found for the original scenario.Moreover, a simple way to enlarge the parameter space is proposed by considering an equivalentlynatural structure for the locking field. Finally, an estimate of the amount of topological defects atthe end of inflation is given; due to the low inflationary scale, it turns out to be negligible.

gr-qc↗