Trans-Planckian Censorship Conjecture Research Articles

Life-time of metastable vacuum in string theory and trans-Planckian censorship conjecture

It has been known that the catalytic effect makes the life-time of a metastable state shorter. We discuss this phenomenon in a decay process of a metastable vacuum in the brane limit of type IIB string theory. Due to the non-linear effect of the DBI action, the bubble created by the decay makes an energetically favorable bound state with an impurity that plays the role of catalyst, which is quite specific to this model and different from other catalysts such as a back hole. Furthermore, we found that this low-energy effective theory around almost unstable regions reduces to a simple quantum mechanical system, and the vacuum life-time can be calculated using known results, even beyond the WKB approximation. Finally, we compare the life-time of the vacuum with the Trans-Planckian Censorship Conjecture (TCC) and find that there is a nonzero window to satisfy the TCC condition for gs ≲ O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O} $$\\end{document}(1).

Trans-Planckian censorship constraints on properties and cosmological applications of axion-like fields

We use the Trans-Planckian Censorship Conjecture (TCC) to constrain the decay constants f characterizing a set of N identical axion-like fields with cosine potentials, improving upon the precision of other Swampland conjectures and existing string-theoretic arguments. We find that consistency with the TCC requires any such set of axion-like fields to satisfy fN≲0.6Mpl, where Mpl is the reduced Planck mass. We show that this bound makes models of axion-driven inflation incapable of simultaneously producing the required number of e-foldings and the observed scalar spectral tilt. In contrast, we find that models of axion quintessence can be simultaneously compatible with the TCC and observational data, provided that the axions' initial field values are set near the maxima of their potentials to within roughly ±π5f.

TCC bounds on the static patch of de Sitter space

Recently, Pei-Ming Ho and Hikaru Kawai [1] have argued that treating particles as wave packets can lead to a shutdown of Hawking radiation after a scrambling time in the case of Schwarzschild black holes. This shutdown arises from viewing quantum field theory near the black hole horizon as an effective field theory, and imposing an appropriate UV cutoff. We show that this effect is also present in the static patch of de Sitter space, leading to a shutdown of Gibbons-Hawking radiation at late times. Assuming this effect is due to the breakdown of effective field theory, we obtain a bound t ≲ H−1 ln(H−1MP) on the time scale of validity of effective field theory in de Sitter space, which matches with the predictions of the Trans-Planckian Censorship Conjecture.

Lagrangian Reconstruction of Barrow Holographic Dark Energy in Interacting Tachyon Model

We consider a correspondence between the tachyon dark energy model and Barrow holographic dark energy (BHDE). The latter is a modified scenario based on the application of the holographic principle with Barrow entropy instead of the usual Bekenstein–Hawking one. We reconstruct the dynamics of the tachyon scalar field T in a curved Friedmann–Robertson–Walker universe both in the presence and absence of interactions between dark energy and matter. As a result, we show that the tachyon field exhibits non-trivial dynamics. In a flat universe, T˙2 must always be vanishing, independently of the existence of interaction. This implies ωD=−1 for the equation-of-state parameter, which in turn can be used for modeling the cosmological constant behavior. On the other hand, for a non-flat universe and various values of the Barrow parameter, we find that T˙2 decreases monotonically for increasing cos(Rh/a) and cosh(Rh/a), where Rh and a are the future event horizon and the scale factor, respectively. Specifically, T˙2≥0 for a closed universe, while T˙2<0 for an open one, which is physically not allowed. We finally comment on the inflation mechanism and trans-Planckian censorship conjecture in BHDE and discuss observational consistency of our model.

Comments on the Transplanckian Censorship Conjecture

We consider some aspects of the Transplanckian Censorship Conjecture (TCC), which states that for theories of quantum gravity there is a limit on the lifetime of dS or quintessence states not too different than the current Hubble horizon. If one accepts the de Sitter Swampland conjecture, then the former are ruled out. We consider some aspects of tunneling to an isolated ground state in the presence of time-varying fields, in quantum mechanics and quantum field theory in the absence of gravitation, and note that lifetimes are typically enormous; in fact, there is often a finite probability for the system to remain eternally in its original state. With gravity in a universe with superluminal expansion, while the field evolution may be slowed, Planck scale fluctuations would seem likely to grow to superhorizon size long before the universe decays. We argue that the TCC, if it is correct, requires that superluminal expansion occur only for a brief period in the history of the universe, and will be followed by a p = ρ phase.

Trans-Planckian Censorship and Spacetime Singularities

We study the effects of trans-Planckian censorship conjecture (TCC) bounds on geodesic completeness of spacetime and the associated existence for an infinite proper time. Using Gronwall’s lemma, TCC bounds can be derived directly, leading to a result about the absence of blowup solutions. We show that the TCC provides part of the required criteria for geodesic completeness, and we then provide the remaining ones, the norm of the extrinsic curvature being bounded away from zero. We also discuss the importance of these results for the classical evolution of Friedmann universes under the assumptions of global and regular hyperbolicity.

Emergent de Sitter cosmology near black hole horizon

We propose an effective model for an exponentially expanding universe in the brane-world scenario. The setup consists of a 5D black hole and a brane close to the black hole horizon. In case the brane acquires a specific configuration, which we deduce from stability arguments, the induced metric outside the black hole horizon on the brane becomes de Sitter in static coordinates. Studying the Einstein equations perturbatively we find the effective gravity on the brane at this level and derive the 4D gravitational constant. Considering a homogeneous and isotropic fluid in the corresponding FLRW coordinates we find that the bulk fluid density inside the brane, which has the same equation of state as the fluid on the brane, contributes to the energy density in the Friedmann equation and therefore in late time may be attributed to dark matter. Studying the stability of the setup we observe that the brane becomes stabilized, in the presence of matter on the brane, with a de Sitter length that is qualitatively of the order of Schwarzschild radius of the universe due to matter. We briefly discuss effects that can bound the de Sitter lifetime. In particular this model can provide a lifetime compatible with Trans-Planckian Censorship conjecture for the current de Sitter phase.

Generic 3-point statistics with tensor modes in light of Swampland and Trans-Planckian Censorship Conjecture

Recently proposed Swampland Criteria (SC) and Trans-Planckian Censorship Conjecture (TCC) question the theoretical consistency of inflationary cosmology. While SC can be in tension with the recent observational bound on tensor-to-scalar ratio which is a consequence of single field consistency relation, the requirement of TCC translates to the fact that inflation can not produce a detectable signal for stochastic gravitational wave, raising a question on future prospects of detection of Primordial Gravitational Waves (PGW). But the constraint can be relaxed significantly by considering Non Bunch Davies (NBD) initial states, that in turn brings back the observational relevance of PGW via its 2-point function. Also with NBD states the tension between SC and observational bound on tensor-to-scalar ratio vanishes. Focusing on these theoretical importance of NBD states, in this article we develop consistent 3-point statistics with tensor modes for all possible correlators (auto and mixed) for NBD initial states in a generic, model independent framework of Effective Field Theory of inflation and analyze the properties of the correlators in the light of TCC. We also construct the templates of the corresponding nonlinearity parameters f_{NL} for different shapes of relevance and investigate if any of the 3-point correlators could be of interest for future CMB missions. Our analysis reveals that the prospects of detecting the tensor auto correlator are almost nil whereas the mixed correlators might be relevant for future CMB missions.

Wave function of the universe in the presence of trans-Planckian censorship

The wave function for a closed de Sitter universe has been computed, demanding consistency with the recently proposed Trans-Planckian Censorship Conjecture (TCC). We extend the Einstein-Hilbert action to contain a complex-valued term which provides an exponentially decaying weight for the geometries violating TCC in the Lorentzian path integral sum while working in the minisuperspace approach to quantum cosmology. This postulated modification suppresses the probability of evolution of the universe into configurations that violate TCC. We show that due to the presence of this suppression factor, the Hubble rate of the universe at the end of the inflation gets subdued and assumes a value less than what is expected classically. Moreover, the consequences of this quantum gravity motivated correction in the primordial power spectrum are discussed as well.

Brane inflation: Swampland criteria, TCC, and reheating predictions

We consider inflation in a five -dimensional space time with the inflaton field confined to live on a brane world. In this scenario, we study different types of potentials for the inflaton, discuss their observational consequences, and compare with data. We find that some class of potentials are in good agreement with observation and that the value of the inflaton field can be sub-Planckian. Moreover, we investigate the swampland criteria in this scenario and determine the consistency of the model with the conjectures. Doing so, we could determine models that simultaneously satisfy both observational data and swampland criteria. More constraints are applied by studying the reheating phase where the acceptable range for the reheating temperature imposes some bounds on the models. As the last step, the result of trans-Planckian censorship conjecture for the model is considered where it is shown the constraint of TCC will be very strong and it could be used to apply limits on the brane tension.

Catalytic creation of a bubble universe induced by quintessence in five dimensions

We investigate the bubble nucleation in five dimensional spacetime catalyzed by quintessence. We especially focus on decay of a metastable Minkowski vacuum to an anti-de Sitter vacuum and study dynamics of the bubble on which four dimensional expanding universe is realized. We also discuss the trans-Planckian censorship conjecture and impose a constraint on the parameter space of the catalysis. As an application of this model, we propose an inflation mechanism and an origin of the dark energy in the context of quintessence in five dimensions.

Brane inflation and trans-Planckian censorship conjecture

The constraint of trans-Planckian censorship conjecture on brane inflation model is considered. The conjectures put an upper bound on the main parameter including temperature, inflation time, potential, and the tensor-to-scalar ratio parameter $r$. It is determined that the resulting constraint could be more stronger than what we have for the standard inflationary models. The constraint in general depends on the brane tension and it is concluded that the conjecture also confined the value of brane tension in order to have consistency for the model. Confining the brane tension turns into a determining value for the five-dimensional Planck mass.

On the Trans-Planckian Censorship Conjecture and the generalized non-minimal coupling

We investigate the Trans-Planckian Censorship Conjecture (TCC) and the arising bounds on the inflationary cosmology caused by that conjecture. In that investigation, we analyze TCC bounds for both Jordan and Einstein frames in the presence of a generic non-minimal coupling (to gravity) term. That term allows us to use the functional freedom it brings to the inflationary Lagrangian as an effective Planck mass. In this sense, we argue one should consider the initial field value of the effective Planck mass for the TCC. We show that as a result, one can remove the TCC upper bounds without the need to produce a new process or go beyond the standard inflation mechanism, with the generalized non-minimal coupling, and for Higgs-like symmetry-breaking potentials.

Asymptotic Safety: Swampland or Wonderland?

We investigate the consequences of combining swampland conjectures with the requirement of asymptotic safety. To this end, we explore the infrared regime of asymptotically safe gravity in the quadratic one-loop approximation, and we identify the hypersurface spanned by the endpoints of asymptotically safe renormalization group trajectories. These comprise the allowed values of higher-derivative couplings, as well as standard logarithmic form factors. We determine the intersection of this hypersurface with the regions of parameter space allowed by the weak-gravity conjecture, the swampland de Sitter conjecture, and the trans-Planckian censorship conjecture. The latter two depend on some order-one constants, for generic values of which we show that the overlap region is a proper subspace of the asymptotically safe hypersurface. Moreover, the latter lies inside the region allowed by the weak gravity conjecture assuming electromagnetic duality. Our results suggest a non-trivial interplay between the consistency conditions stemming from ultraviolet completeness of the renormalization group flow, black hole physics, and cosmology.

De Sitter quantum breaking, swampland conjectures and thermal strings

We argue that under certain assumptions the quantum break time approach and the trans-Planckian censorship conjecture both lead to de Sitter swampland constraints of the same functional form. It is a well known fact that the quantum energy-momentum tensor in the Bunch-Davies vacuum computed in the static patch of dS breaks some of the isometries. Proposing that this is a manifestation of quantum breaking of dS, we analyze some of its consequences. In particular, this leads to a thermal matter component that can be generalized to string theory in an obvious way. Imposing a censorship of quantum breaking, we recover the no eternal inflation bound in the low temperature regime, while the stronger bound from the dS swampland conjecture follows under a few reasonable assumptions about the still mysterious, presumably topological, high-temperature regime of string theory.

Swampland de Sitter conjectures in no-scale supergravity models

It is challenging to construct explicit and controllable models that realize de Sitter solutions in string compactifications. This difficulty is the main motivation for the refined de Sitter conjecture and the trans-Planckian censorship conjecture which forbid stable de Sitter solutions but allow metastable, unstable and rolling solutions in a theory consistent with quantum gravity. Inspired by this, we first study a toy de Sitter no-scale supergravity model and show that for particular choices of parameters it can be consistent with the refined de Sitter conjecture and the trans-Planckian censorship conjecture. Then we modify the model by adding rolling dynamics and show that the theory can become stable along the imaginary direction, where it would otherwise be unstable. We extend the model to multifield rolling and de Sitter fields, finding the parameter space where they can be compatible with the refined de Sitter conjecture. The modified models with rolling fields can be used to construct quintessence models to accommodate the accelerating expansion of the Universe.

Consistency of Cubic Galileon Cosmology: Model-Independent Bounds from Background Expansion and Perturbative Analyses

We revisit the cosmological dynamics of the cubic Galileon model in light of the recently proposed model-independent analyses of the Pantheon supernova data. At the background level, it is shown to be compatible with data and preferred over standard quintessence models. Furthermore, the model is shown to be consistent with the trans-Planckian censorship conjecture (as well as other Swampland conjectures). It is shown that for the given parametrization, the model fails to satisfy the bounds on the reconstructed growth index derived from the Pantheon data set at the level of linear perturbations.

Thermal, trapped and chromo-natural inflation in light of the swampland criteria and the trans-Planckian censorship conjecture

We consider thermal, trapped and chromo-natural inflation in light of the swampland criteria and the Trans-Planckian Censorship Conjecture (TCC). Since thermal inflation occurs at energies low compared to those of Grand Unification, it is consistent with the TCC, and it is also consistent with the refined swampland conditions. Trapped and chromo-natural inflation are candidates for primordial (high energy scale) inflation. Since in both of these scenarios there are effective damping terms in the scalar field equation of motion, the models can easily be consistent with the swampland criteria. The TCC, on the other hand, constrains these scenarios to only take place at low energies.

Cosmological trans-Planckian conjectures are not effective

It is remarkable that the primordial fluctuations as revealed by the CMB coincide with what quantum fluctuations would look like if they were stretched across the sky by accelerated cosmic expansion. It has been observed that this same stretching also brings very small — even trans-Planckian — length scales up to observable sizes if extrapolated far enough into the past. This potentially jeopardizes later descriptions of late-time cosmology by introducing uncontrolled trans-Planckian theoretical errors into all calculations. Recent speculations, such as the Trans-Planckian Censorship Conjecture (TCC), have been developed to avoid this problem. We revisit old arguments why the consistency of (and control over) the Effective Field Theory (EFT) governing late-time cosmology is not necessarily threatened by the descent of modes due to universal expansion, even if EFT methods may break down at much earlier times. Failure of EFT methods only poses a problem if late-time predictions rely on non-adiabatic behaviour at these early times (such as is often true for bouncing cosmologies, for example). We illustrate our arguments using simple non-gravitational examples such as slowly rolling scalar fields and the spacing between Landau levels for charged particles in slowly varying magnetic fields, for which similar issues arise and are easier to understand. We comment on issues associated with UV completions. Our arguments need not invalidate speculative ideas like the TCC but suggest they are not required by the present evidence.

The Trans-Planckian Censorship Conjecture in Different Frameworks of Viable Inflation

We review the recently proposed Trans-Planckian Censorship Conjecture (TCC) that stems from the trans-Planckian problem of cosmological perturbations. We analyze the implications and constraints that the TCC introduces in different frameworks of viable inflation. We revisit the case of slow-roll scalar field inflation and we investigate the cases of slow-roll f(R) and f(R,ϕ)-gravity. Finally, we consider the conjecture in the context of constant-roll scalar field inflation.