Search

It is shown in this article that an explicit construction of a four‐dimensional de Sitter space may be performed using a diagrammatic approach via nodal diagrams emanating from the path integral representation of the Glauber‐Sudarshan state. Sum of these diagrams typically leads to an asymptotic series of Gevrey kind which can then be Borel resummed, thus reproducing the non‐perturbative structure of the system. The analysis shows that four‐dimensional de Sitter space is not only possible in string theory overcoming the no‐go and the swampland criteria—albeit as a Glauber‐Sudarshan state—but it may also be non‐perturbatively stable within a controlled temporal domain. Somewhat consistently, the Borel resummation of the Gevrey series provides strong hint towards the positivity of the cosmological constant. [ABSTRACT FROM AUTHOR]

It is now widely believed that if the gravitational field is (perturbatively) quantum, it would entangle two massive objects (in spatial superpositions) which were otherwise unentangled to begin with. Recently, actual table-top experiments have been proposed to test this idea in what would be the first detection of perturbative quantum gravity. In this essay, we devise a thought experiment to prove that such gravity-induced entanglement depends on the spacetime curvature and can, in principle, act as an alternate signature of the expanding background. This will open up new and complementary directions to search for such entanglement in curved spacetime and reveal fresh perspectives on it. [ABSTRACT FROM AUTHOR]

We review a proposal to obtain an emergent metric space-time and an emergent early universe cosmology from the Banks–Fischler–Shenker–Susskind (BFSS) matrix model. Some challenges and directions for future research are outlined. [ABSTRACT FROM AUTHOR]

Although the paradigm of inflation has been extensively studied to demonstrate how macroscopic inhomogeneities in our Universe originate from quantum fluctuations, most of the established literature ignores the crucial role that entanglement between the modes of the fluctuating field plays in its observable predictions. In this paper, we import techniques from quantum information theory to reveal hitherto undiscovered predictions for inflation which, in turn, signals how quantum entanglement across cosmological scales can affect large scale structure. Our key insight is that observable long-wavelength modes must be part of an open quantum system, so that the quantum fluctuations can decohere in the presence of an environment of short-wavelength modes. By assuming the simplest model of single-field inflation, and considering the leading order interaction term from the gravitational action, we derive a universal lower bound on the observable effect of such inescapable entanglement. Although this signal is too weak for direct detection in the foreseeable future, we discuss the importance of its theoretical implications. [ABSTRACT FROM AUTHOR]

The BFSS matrix model is a suggested nonperturbative definition of string theory. Starting from a thermal state of this matrix model, we show how space and time can emerge dynamically. Results from the IKKT matrix model indicate that the SO(9) symmetry of space is spontaneously broken to SO(3) × SO(6), with the three-dimensional subspace becoming large. Given this initial state for the universe, we show that cosmological perturbations and gravitational waves with scale-invariant spectra are generated, without the need of postulating an early phase of cosmological inflation. The Big Bang singularity is automatically resolved. [ABSTRACT FROM AUTHOR]

Using the fact that we only observe those modes that exit the Hubble horizon during inflation, one can calculate the entanglement entropy of such long-wavelength perturbations by tracing out the unobservable sub-Hubble fluctuations they are coupled with. On requiring that this perturbative entanglement entropy, which increases with time, obey the covariant entropy bound for an accelerating background, we find an upper bound on the duration of inflation. This presents a new perspective on the (meta-)stability of de Sitter spacetime and an associated lifetime for it. [ABSTRACT FROM AUTHOR]

We provide further evidence to support the fact that a four‐dimensional effective field theory description with de Sitter isometries in IIB string theory, overcoming the no‐go and the swampland criteria, can only exist if de Sitter space is realized as a Glauber‐Sudarshan state. We show here that this result is independent of the choice of de Sitter slicings. The Glauber‐Sudarshan state, constructed by shifting the interacting vacuum in the M‐theory uplift of the scenario, differs from a standard coherent state in QFT in the sense that the shape and size of the state changes with respect to time, implying changes in the graviton and the flux quanta. Despite this, the expectation values of the graviton and flux operators in such a state reproduce the exact de Sitter background, as long as we are within the temporal bound set by the onset of the strong coupling in the dual type IIA side, and satisfy the corresponding Schwinger‐Dyson's equations in the presence of hierarchically controlled perturbative and non‐perturbative quantum corrections. Additionally, we provide a detailed study of the fluxes supporting the Glauber‐Sudarshan state in the M‐theory uplift of the IIB scenario. We show explicitly how the Bianchi identities, anomaly cancellation and flux quantization conditions, along‐with the constraints from the Schwinger‐Dyson's equations, conspire together to provide the necessary temporal dependences to support such a state in full M‐theory. We also discuss how our analysis points towards a surprising connection to the four‐dimensional null energy condition, for a Friedman‐Lemaitre‐Robertson‐Walker state in the IIB side, as a consistency condition for the existence of an effective field theory description in M‐theory. The authors provide further evidence to support the fact that a four‐dimensional effective field theory description with de Sitter isometries in IIB string theory, overcoming the no‐go and the swampland criteria, can only exist if de Sitter space is realized as a Glauber‐Sudarshan state. It is shown here that this result is independent of the choice of de Sitter slicings. The Glauber‐Sudarshan state, constructed by shifting the interacting vacuum in the M‐theory uplift of the scenario, differs from a standard coherent state in QFT in the sense that the shape and size of the state changes with respect to time, implying changes in the graviton and the flux quanta. Despite this, the expectation values of the graviton and flux operators in such a state reproduce the exact de Sitter background, as long as we are within the temporal bound set by the onset of the strong coupling in the dual type IIA side, and satisfy the corresponding Schwinger‐Dyson's equations in the presence of hierarchically controlled perturbative and non‐perturbative quantum corrections. Additionally, a detailed study of the fluxes supporting the Glauber‐Sudarshan state in the M‐theory uplift of the IIB scenario will be provided. It will be shown explicitly how the Bianchi identities, anomaly cancellation and flux quantization conditions, along‐with the constraintsfrom the Schwinger‐Dyson's equations, conspire together to provide the necessary temporaldependences to support such a state in full M‐theory. There will be a discussion how the analysis given here points towards a surprising connection to the four‐dimensional null energy condition, for a Friedman‐Lemaitre‐Robertson‐Walker state in the IIB side, as a consistency condition for the existence of an effective field theory description in M‐theory. [ABSTRACT FROM AUTHOR]

We examine the recently introduced idea of Spin-Field Correspondence (SFC) focusing on the example of the spin system described by the XXZ Heisenberg model with external magnetic field. The Hamiltonian of the resulting nonlinear scalar field theory is derived for arbitrary value of the anisotropy parameter Δ. We show that the linear scalar field theory is reconstructed in the large spin limit. For Δ = 1 , a nonrelativistic scalar field theory satisfying the Born reciprocity principle is recovered. As expected, for the vanishing anisotropy parameter Δ → 0 , the standard relativistic Klein–Gordon field is obtained. Various aspects of the obtained class of the scalar fields are studied, including the fate of the relativistic symmetries and the properties of the emerging interaction terms. We show that, in a certain limit, the so-called polymer quantization of the field variables is recovered. This and other discussed properties suggest a possible relevance of the considered framework in the context of quantum gravity. [ABSTRACT FROM AUTHOR]

We analyze four-dimensional Friedmann-Lemaître-Robertson-Walker cosmologies in type IIB, arising from a M-theory dual, and find that the null energy condition (NEC) has to be obeyed by them (except for the negatively curved case) in order for the M-theory action to have a Wilsonian effective description. However, this does not imply that the M-theory metric has to obey the 11D NEC. Thus, we propose a new swampland conjecture? the 4D NEC is a consistency condition for any theory to have a completion within M theory-with an explicit derivation of it for cosmological backgrounds from a top-down perspective. We briefly discuss the cosmological consequences of such a condition derived from M theory. [ABSTRACT FROM AUTHOR]

Weak magnetic monopoles with a continuum of charges less than the minimum implied by Dirac's quantization condition may be possible in nonassociative quantum mechanics. If a weakly magnetically charged proton in a hydrogen atom perturbs the standard energy spectrum only slightly, magnetic charges could have escaped detection. Testing this hypothesis requires entirely new methods to compute energy spectra in nonassociative quantum mechanics. Such methods are presented here, and evaluated for upper bounds on the magnetic charge of elementary particles. [ABSTRACT FROM AUTHOR]

New and nontrivial properties of off-shell instantons in loop quantum cosmology show that dynamical signature change naturally cures recently observed problems in the semiclassical path integral of quantum gravity. If left unsolved, these problems would doom any theory of smooth initial conditions of the Universe. The no-boundary proposal, as a specific example of such a theory, is rescued by loops, presenting a rare instance of a fruitful confluence of different approaches to quantum cosmology. [ABSTRACT FROM AUTHOR]

The familiar concepts of state vectors and operators in quantum mechanics rely on associative products of observables. However, these notions do not apply to some exotic systems such as magnetic monopoles, which have long been known to lead to nonassociative algebras. Their quantum physics has remained obscure. This Letter presents the first derivation of potentially testable physical results in nonassociative quantum mechanics, based on effective potentials. They imply new effects which cannot be mimicked in usual quantum mechanics with standard magnetic fields. [ABSTRACT FROM AUTHOR]

The lack of rotating black hole models, which are typically found in nature, in loop quantum gravity (LQG) substantially hinders the progress of testing LQG from observations. Starting with a nonrotating LQG black hole as a seed metric, we construct a rotating spacetime using the revised Newman-Janis algorithm. The rotating solution is nonsingular everywhere and it reduces to the Kerr black hole asymptotically. In different regions of the parameter space, the solution describes (1) a wormhole without event horizon (which, we show, is almost ruled out by observations), (2) a black hole with a spacelike transition surface inside the event horizon, or (3) a black hole with a timelike transition region inside the inner horizon. It is shown how fundamental parameters of LQG can be constrained by the observational implications of the shadow cast by this object. The causal structure of our solution depends crucially only on the spacelike transition surface of the nonrotating seed metric, while being agnostic about specific details of the latter, and therefore captures universal features of an effective rotating, nonsingular black hole in LQG.