De Sitter Swampland Conjecture Research Articles

Hořava–Lifshitz F(R) Theories and the Swampland

The compatibility between the de Sitter Swampland conjecture and Hořava–Lifshitz F(R¯) theories with a flat FLRW metric is studied. We first study the standard f(R) theories and show that the only way in which the dS conjecture can be made independent of R is by considering a power law of the form f(R)∼Rγ. The conjecture and the consistency of the theory puts restrictions on γ to be greater but close to one. For F(R¯) theories described by its two parameters λ and μ, we use the equations of motion to construct the function starting with an ansatz for the scale factor in the Jordan frame of the power law form. By performing a conformal transformation on the three metric to the Einstein frame, we can obtain an action of gravity plus a scalar field by relating the parameters of the theory. The non-projectable and projectable cases are studied and the differences are outlined. The obtained F(R¯) function consists of terms of the form R¯γ with the possibility of having negative power terms. The dS conjecture leads to inequalities for the λ parameter; in both versions, it becomes restricted to be greater but close to 1/3. We can also study the general case in which μ and λ are considered as independent. The obtained F function has the same form as before. The consistency of the theory and the dS conjecture lead to a set of inequalities on both parameters that are studied numerically. In all cases, λ is restricted by μ around 1/3, and we obtain λ→1/3 if μ→0. We consider the f(R) limit μ,λ→1 and we obtain consistent results. Finally, we study the case of a constant Hubble parameter. The dS conjecture can be fulfilled by restricting the parameters of the theory; however, the constraint makes this compatibility exclusive to these kinds of theories.

De Sitter swampland conjecture in string field inflation

In this paper, we study a particular type of inflation by using non-local Friedman equations that are derived from the zero levels of string field theory and express a tachyonic action. Then, we challenge it by further refining de Sitter (dS) swampland conjecture (FRdSSC) monitoring. Therefore, we investigate some quantities, such as potential and Hubble parameters. We also consider slow-roll parameters to examine quantities such as the scalar spectrum index and the tensor-to-scalar ratio. Using straightforward calculations, we investigate this model from the swampland conjecture perspective in terms of the cosmological parameters, i.e., (n_s), (r), and observable data such as Planck 2018, by constructing some structures such as (c_{1,2}-n_s) and (c_{1,2}-r_s). Then, we make a new restriction for this conjecture as c_1^2c_2^2 and get a limit for this model in the range c<0.0942. We find this inflationary model is strongly in tension with the dS swampland conjecture (dSSC), i.e., c_1=c_2 ne {mathcal {O}}(1). So, we shall challenge it with the FRdSSC, which has some free parameters, viz., a,b>0, a+b=1, and q>2. By setting these parameters, we examine the compatibility of the mentioned conjecture with this inflationary model. Finally, we infer from this string field inflation (SFI) model that it satisfies the FRdSSC with the constraint of its free parameters a, b, and q.

DS4 universe emergent from Kerr-AdS5 spacetime: bubble nucleation catalyzed by a black hole

The emergence of a four-dimensional de Sitter (dS4) universe on an expanding bubble in the five-dimensional anti-de Sitter (AdS5) background has been suggested as a possible cosmological scenario. It is motivated by the difficulties in the realization of a stable de Sitter vacua in string theory. The bubble can be nucleated in a meta-stable pure AdS5 spacetime, but it is known that a pure AdS spacetime is non-perturbatively unstable. It means that the pure AdS5 background is an idealized situation, and in realistic situations, non-linear perturbations in AdS may lead to the formation of black holes due to the gravitational turbulent instability. To investigate how the proposed scenario works in a more realistic situation, we here study the nucleation process of a vacuum bubble in the Kerr-AdS5 spacetime. Especially we investigate conditions sufficient to ensure the nucleation of a vacuum bubble with a rotating black hole and how the black hole affects the transition rate. We find that even in the Kerr-AdS5 spacetime, a quasi-dS4 expansion can be realized on the nucleated vacuum bubble without contradicting the de Sitter swampland conjectures.

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.

Theories of gravity with nonminimal matter-curvature coupling and the de Sitter swampland conjectures

We discuss, in the context of alternative theories of gravity with nonminimal coupling between matter and curvature, if inflationary solutions driven by a single scalar field can be reconciled with the swampland conjectures about the emergence of de Sitter solutions in string theory. We find that the slow-roll conditions are incompatible with the swampland conjectures for a fairly generic inflationary solution in such alternative theories of gravity.

Completely dark matter from rapid-turn multifield inflation

We study cosmological gravitational particle production as applied to “rapid-turn” models of inflation involving two scalar fields. We are interested in the production of massive spin-0 particles that only interact gravitationally and provide a candidate for the dark matter. Specifically, we study two models of rapid-turn multifield inflation, motivated in part by the de Sitter swampland conjecture, that are distinguished by the curvature of field space and the presence or absence of field space ‘angular momentum’ conservation. We find that one of these models leads to insufficient particle production and cannot explain the observed dark matter relic abundance. The second model is able to explain the origin of spin-0 dark matter via gravitational production, and we identify the relevant region of parameter space that is consistent with measurements of the dark-matter relic abundance, the dark-matter-photon isocurvature perturbations, and the spectrum of curvature perturbations that is probed by cosmological observations. Our work demonstrates the compatibility of the de Sitter swampland conjecture with completely dark matter.

Composite inflation and further refining dS swampland conjecture

A natural combination of the first and second derivatives of the scalar potential was achieved in a framework of an alternative refined de Sitter conjecture recently proposed in the literature. In this work, we study various inflation models in which the inflaton is a composite field emerging from various strongly interacting field theories. We then examine if these four models of inflation can satisfy this further refining de Sitter swampland conjecture or not. Regarding our analysis with proper choices of parameters a,b=1−a and q, we find that some inflationary models are in strong tension with the refined Swampland conjecture. However, all of them can always satisfy the alternative refined de Sitter conjecture. Therefore, one may expect that all inflationary models might all be in “landscape” since the “further refining de Sitter swampland conjecture” is satisfied.

Scalar Weak Gravity Conjecture in Super Yang-Mills Inflationary Model

In this article, we want to check four inflation models, namely, composite NJL inflation (NJLI), Glueball inflation (GI), super Yang–Mills inflation (SYMI), and Orientifold inflation (OI), with two conjectures of the swampland program: scalar weak gravity conjecture (SWGC) and strong scalar weak gravity conjecture (SSWGC) since all these models violate the dS swampland conjecture (DSC) but are compatible with further refining de Sitter swampland conjecture (FRDSSC) through manual adjustment of free parameters of the mentioned conjecture. We want to study the simultaneous compatibility of each model with these two new conjectures. Despite being consistent with (FRDSSC), we find that all models are not compatible with the other conjectures of the Swampland program in all regions, and these conjectures are only satisfied in a specific area. Moreover, due to the presence of constant parameter (ϕ0) in the higher orders derivatives, the (SYMI) and (OI) among all the models are more compatible with all conjectures of the swampland program. These models can provide a more significant amount of satisfaction with all of them. They can be suitable and accurate inflation models for a more profound examination of universe developments. We determined a particular region for these models is compatible with (FRDSSC), (SWGC), and (SSWGC) simultaneously.

Notes on further refining de Sitter swampland conjecture with inflationary models

In this paper, we challenge some inflationary models with the recent new conjecture of the swampland program, namely, further refining the de Sitter swampland conjecture. So far, different inflation models have been studied with refined dS swampland conjecture in various conditions. Some of these models were in line with this conjecture, and some were in direct tension with it. Therefore, a modified model that combines the first and second conditions of refined dS conjecture was proposed. It has a limitation on its constant parameters such as a , b = 1 − a and q . We challenge several inflation models with the new conjecture, which contradicts the refined dS conjecture. We discuss the constraints and adjustments of each of a , b = 1 − a , and q and the compatibility or incompatibility of the inflation models with further refining the de Sitter swampland conjecture. We will compare the results with the models studied by refined dS conjecture. We conclude that many inflation models are fully compatible with the mentioned conjecture. If the new conjecture is accurate, these inflationary models live in the landscape instead of the swampland. • Further refining de sitter swampland conjecture. • Minimal gauge inflation model. • Minimal plateau inflationary model. • Gauged Nambu–Jona–Lasinio inflation. • limitations applied to its free constant parameters.

Multi-field cold and warm inflation and the de Sitter swampland conjectures

We discuss under which conditions multi-field cold and warminflationary models with canonical kinetic energy terms are compatiblewith the swampland conjectures about the emergence of de Sitter solutionsin string theory. We find that under quite general conditions the slow-rollconditions for multi-field cold inflation are at odds with the swamplandconjectures for an arbitrary number of scalar fields driving inflation.However, slow-roll conditions can be reconciled with the swampland conjecturesin the strong dissipative regime of warm inflation.

Cosmological dynamics of multifield dark energy

We numerically and analytically explore the background cosmological dynamics of multifield dark energy with highly nongeodesic or "spinning" field-space trajectories. These extensions of standard single-field quintessence possess appealing theoretical features and observable differences from the cosmological standard model. At the level of the cosmological background, we perform a phase-space analysis and identify approximate attractors with late-time acceleration for a wide range of initial conditions. Focusing on two classes of field-space geometry, we derive bounds on parameter space by demanding viable late-time acceleration and the absence of gradient instabilities, as well as from the de Sitter swampland conjecture.

Refined swampland conjecture in deformed Starobinsky gravity

In order to validate or invalidate a large class of low energy effective theories, the swampland conjecture has attracted significant attention recently. It can be stated as inequalities on the potential of a scalar field which is conjectured to satisfy certain constraints. In this work, we discuss the theoretical viability of deformed Starobinsky gravity in light of the refined swampland conjectures. We consider the deformation of the form [Formula: see text] with [Formula: see text] being a constant. We then constrain [Formula: see text] using the spectral index of curvature perturbation [Formula: see text] and the tensor-to-scalar ratio [Formula: see text]. We demonstrate that the model under consideration is in strong tension with the refined swampland conjecture. However, regarding our analysis with proper choices of parameters [Formula: see text] and [Formula: see text], we discover that the model can always satisfy this new refined swampland conjecture. Therefore, the model might be in “landscape” since the “further refining de Sitter swampland conjecture” is satisfied.

Further Refining Swampland Conjecture on Inflation in General Scalar‐Tensor Theories of Gravity

AbstractAn alternative refined de Sitter conjecture giving rise to a natural combination of the first and second derivatives of the scalar potential was proposed recently by David Andriot and Christoph Roupec (Fortsch. Phys. 67 (2019) no.1‐2, 1800105). In this work, we study the inflation models in a general scalar‐tensor theory with exponential and hyperbolic tangent forms of potential as well as model with quantum corrected potential and examine whether these three models of inflation can satisfy this further refining de Sitter swampland conjecture or not. Regarding our analysis with proper choices of parameters and q, we find that these three inflationary models can always satisfy this new refined swampland conjecture. Therefore, all three inflationary models might all be in “landscape” since the “further refining de Sitter swampland conjecture” is satisfied.

Rapid-turn inflation in supergravity is rare and tachyonic

Strongly non-geodesic, or rapidly turning trajectories in multifield inflation have attracted much interest recently from both theoretical and phenomenological perspectives. Most models with large turning rates in the literature are formulated as effective field theories. In this paper we investigate rapid-turn inflation in supergravity as a first step towards understanding them in string theory. We find that large turning rates can be generated in a wide class of models, at the cost of high field space curvature. In these models, while the inflationary trajectories are stable, one Hessian eigenvalue is always tachyonic and large, in Hubble units. Thus, these models satisfy the de Sitter swampland conjecture along the inflationary trajectory. However, the high curvatures underscore the difficulty of obtaining rapid-turn inflation in realistic string-theoretical models.In passing, we revisit the η-problem in multifield slow-roll inflation and show that it does not arise, inasmuch as the inflatons, ϕi , can all be heavier (in absolute value) that the Hubble scale: |mi |/H>1, ∀i.

Higgs inflation and its extensions and the further refining dS swampland conjecture

On the one hand, Andriot and Roupec (Fortsch Phys, 1800105, 2019) proposed an alternative refined de Sitter conjecture, which gives a natural condition on a combination of the first and second derivatives of the scalar potential (Andriot and Roupec 2019). On the other hand, in our previous article (Liu in Eur Phys J Plus 136:901, 2021) , we have found that Palatini Higgs inflation model is in strong tension with the refined de Sitter swampland conjecture (Liu 2021). Therefore, following our previous research, in this article we examine if Higgs inflation model and its two variations: Palatini Higgs inflation and Higgs-Dilaton model (Rubio in Front Astron Space Sci, https://doi.org/10.3389/fspas.2018.00050, 2019) can satisfy the “further refining de Sitter swampland conjecture” or not. Based on observational data (Ade et al., Phys Rev Lett 121:221301, 2018; Akrami et al., Planck 2018 results. X. Constraints on inflation, arXiv:1807.06211 [astro-ph.CO], 2018; Aghanim et al., Planck 2018 results: VI. Cosmological parameters, arXiv:1807.06209 [astro-ph.CO], 2018), we find that these three inflationary models can always satisfy this new swampland conjecture if only we adjust the relevant parameters a, b = 1-a and q. Therefore, if the “further refining de Sitter swampland conjecture” does indeed hold, then the three inflationary models might all be in “landscape”.

A solution to the de Sitter swampland conjecture versus inflation tension via supergravity

The methods of supergravity allow us to derive a multi-field F-term potential. Using this, we denote a generic and non-positive single-field F-term potential. We insert our theory into the scalar-gravity part of the (2,1|1) invariant superconformal action. That action leads us to a de Sitter solution at the inflationary trajectory. One can denote stabilization of fields in terms of the Kähler kinetic terms and single-field slow-roll inflation parameters. We combine these with the de Sitter swampland conjecture to generate a bounded conjecture. This approach allowed us to show that the single field slow-roll inflation works in harmony with bounded de Sitter conjecture for any concave inflation potential.

Generalizing the swampland: Embedding P(X,φ) inflationary theories in a curved multifield space

We study the general embedding of a $ P(X, \varphi) $ inflationary theory into a two-field theory with curved field space metric, which was proposed as a possible way to examine the relation between de Sitter Swampland conjecture and \textit{k}-inflation. We show that this embedding method fits into the special type of two-field model in which the heavy field can be integrated out at the full action level. However, this embedding is not exact due to the upper bound of the effective mass of the heavy field. We quantify the deviation between the speed of sound calculated via the $ P(X, \varphi) $ theory and the embedding two-field picture to next leading order terms. We especially focus on the first potential slow roll parameter defined in the two-field picture and obtain an upper bound on it.

Notes on quantum corrections of swampland and trans-Planckian censorship conjectures

We discuss the de Sitter swampland and trans-Planckian censorship conjectures (TCC) from the entropy bound with quantum corrections, namely quantum version of Bousso's bound and energy conditions. We include the typical contributions from the entanglement entropy in quasi-de Sitter spacetime. The TCC is not much corrected, whereas the bounds on de Sitter swampland conjecture from energy conditions can be relaxed due to quantum corrections.

An update on moduli stabilization with antibrane uplift

It was recently shown that in warped compactifications based on a Klebanov-Strassler throat there is a light complex structure field, governing the size of the throat and the redshift at its tip. We show that after uplift of the cosmological constant by an anti-D3 brane at the tip of the throat, the contribution to supersymmetry breaking coming from the new light field is large. We work out the mass scales, in particular the condition for this field to be heavier than the Kähler modulus. We check that for the range of parameters relevant for the destabilization we find agreement with de Sitter swampland conjecture. Adding matter fields on distant branes, we discuss the effects on supersymmetry breaking in the observable sector. A hierarchically small scale of supersymmetry breaking translates generically into large values of localized D3 charges in the manifold.

Obstacles to constructing de Sitter space in string theory

There have been many attempts to construct de Sitter space-times in string theory. While arguably there have been some successes, this has proven challenging, leading to the de Sitter swampland conjecture: quantum theories of gravity do not admit stable or metastable de Sitter space. Here we explain that, within controlled approximations, one lacks the tools to construct de Sitter space in string theory. Such approximations would require the existence of a set of (arbitrarily) small parameters, subject to severe constraints. But beyond this one also needs an understanding of big-bang and big-crunch singularities that is not currently accessible to standard approximations in string theory. The existence or non-existence of metastable de Sitter space in string theory remains a matter of conjecture.