dS Swampland Conjecture Research Articles

Dark dimension gravitons as dark matter

We consider cosmological aspects of the Dark Dimension (a mesoscopic dimension of micron scale), which has recently been proposed as the unique corner of the quantum gravity landscape consistent with both the Swampland criteria and observations. In particular we show how this leads, by the universal coupling of the Standard Model sector to bulk gravitons, to massive spin 2 KK excitations of the graviton in the dark dimension (the “dark gravitons”) as an unavoidable dark matter candidate. Assuming a lifetime for the current de Sitter phase of our universe of order Hubble, which follows from both the dS Swampland Conjecture and TCC, we show that generic features of the dark dimension cosmology can naturally lead to the correct dark matter density and a resolution of the cosmological coincidence problem, where the matter/radiation equality temperature (T ~ 1 eV) coincides with the temperature where the dark energy begins to dominate. Thus one does not need to appeal to Weinberg’s anthropic argument to explain this coincidence. The dark gravitons are produced at T ~ 4 GeV, and their composition changes as they mainly decay to lighter gravitons, without losing much total mass density. The mass of dark gravitons is mDM ∼ 1 − 100 keV today.

(In)stability of de Sitter vacuum in light of distance conjecture and emergence proposal

The distance conjecture claims that as the modulus traverses along the trans-Planckian geodesic distance, the effective field theory becomes invalid by a descent of a tower of states from UV. Moreover, according to the recent (strong version of) emergence proposal, the kinetic term of the modulus is entirely generated by the wavefunction renormalization in which a tower of states are integrated out. Assuming these two conjectures, we explore the role of a tower of states coupled to the modulus in (in)stability of the de Sitter (dS) vacuum by studying the one-loop effective potential generated by a tower of states. We find that a fermionic tower of states makes the effective potential more or less consistent with the dS swampland conjecture: either the slope or the curvature of the potential is sizeable. In contrast, the effective potential generated by a bosonic tower of states seems to allow the stable dS vacuum. Therefore, in order to argue the instability of the dS vacuum, the additional ingredient like supersymmetry breaking needs to be taken into account.

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.

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.

Information paradox and island in quasi-de Sitter space

Whereas a static observer in de Sitter (dS) space detects thermal radiation emitted by the horizon, the dS isometries impose that the radiation is in equilibrium with the background. This implies that for the static observer to find the information paradox, the background must be deformed to quasi-dS space in which the dS isometries are spontaneously broken. We study the condition that the information paradox arises in quasi-dS space with the monotonically increasing horizon size which is used to describe the inflationary cosmology. For this purpose, the dimensional reduction of three-dimensional dS space with thermal radiation modelled by the JT gravity coupled to CFT is considered. We argue that when the central charge monotonically increases in time, the information paradox arises but the conditions for the existence of the island become more restrictive. As the central charge can be interpreted as the number of degrees of freedom, the absence of the island in quasi-dS space supports the entropy argument for the dS swampland conjecture.

Cosmic Evolution of the Logarithmic f(R) Model and the dS Swampland Conjecture

In this paper, we study the inflationary scenario in logarithmic f(R) gravity, where the rate of inflation roll is constant. On the other hand, our gravitational f(R) model is a polynomial plus a logarithmic term. We take advantage of constant-roll conditions and investigate the cosmic evolution of the logarithmic f(R) gravity. We present a numerical and a graphical study using the model parameters. Additionally, we obtain the corresponding potential by using the constant-roll condition. We obtain the exact value of the potential satisfying the constant-roll conditions. Next, we challenge it with refined swampland conjecture with respect to the Planck data. Finally, we compare our results with the latest observable data.

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.

Higgs inflation and scalar weak gravity conjecture

In this article, we intend to find a specific model which can satisfy the further refining dS swampland conjecture and scalar weak gravity conjecture (SWGC) simultaneously, in particular, Higgs inflation model and its two extensions: Higgs-dilaton model and Palatini Higgs inflation. We determine the conditions if the three inflation models satisfy scalar weak gravity conjecture (SWGC) and strong scalar weak gravity conjecture (SSWGC).

Stringy multifield quintessence and the Swampland

We consider quintessence models within 4D effective descriptions of gravity coupled to two scalar fields. These theories are known to give rise to viable models of late-time cosmic acceleration without any need for flat potentials, and so they are potentially in agreement with the dS Swampland conjecture. In this paper we investigate the possibility of consistently embedding such constructions in string theory. We identify situations where the quintessence fields are either closed string universal moduli or non-universal moduli such as blow-up modes. We generically show that no trajectories compatible with today’s cosmological parameters exist, if one starts from matter-dominated initial conditions. It is worth remarking that universal trajectories compatible with observations do appear, provided that the starting point at early times is a phase of kinetic domination. However, justifying this choice of initial conditions on solid grounds is far from easy. We conclude by studying Q-ball formation in this class of models and discuss constraints coming from Q-ball safety in all cases analyzed here.

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.

IR/UV mixing, towers of species and swampland conjectures

By applying the Covariant Entropy Bound (CEB) to an EFT in a box of size 1/ΛIR one obtains that the UV and IR cut-offs of the EFT are necessarily correlated. We argue that in a theory of Quantum Gravity (QG) one should identify the UV cutoff with the ‘species scale’, and give a general algorithm to calculate it in the case of multiple towers becoming light. One then obtains an upper bound on the characteristic mass scale of the tower in terms of the IR cut-off, given by Mtower ≲ {left({Lambda}_{mathrm{IR}}right)}^{2{alpha}_D} in Planck units, with αD = (D − 2 + p)/2p(D − 1), where p depends on the density of states. Identifying the IR cut-off with a (non-vanishing) curvature in AdS one reproduces the statement of the AdS Distance Conjecture (ADC), also giving an explicit lower bound for the α exponent. In particular, we find that the CEB implies α ≥ 1/2 in any dimension if there is a single KK tower, both in AdS and dS vacua. However values α < 1/2 are allowed if the particle tower is multiple or has a string component. We also consider the CKN constraint coming from avoiding gravitational collapse which further requires in general α ≥ 1/D for the lightest tower. We analyse the case of the DGKT-CFI class of Type IIA orientifold models and show it has both particle and string towers below the species scale, so that a careful analysis of how the ADC is defined is needed. We find that this class of models obey but do not saturate the CEB. The UV/IR constraints found apply to both AdS and dS vacua. We comment on possible applications of these ideas to the dS Swampland conjecture as well as to the observed dS phase of the universe.

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”.

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.

Is gravity the weakest force?

It has recently been suggested that ‘gravity is the weakest force’ in any theory with a suitable UV completion within quantum gravity. One formulation of this statement is the scalar weak gravity conjecture (WGC), which states that gravity is weaker than the force originating from scalar fields. We study the scalar WGC in de Sitter (dS) space, and discuss its low-energy consequences in light of the experimental searches for fifth forces and violations of the equivalence principle. We point out that some versions of the scalar WGC forbid the existence of very light scalar particles, such as the quintessence and axion-like particles. The absence of the quintessence field means that these versions of the scalar WGC are in phenomenological tension with the recently-proposed dS swampland conjecture and its refinements. Some other versions of the scalar WGC escape these constraints, and could have interesting phenomenological consequences.

Trans-Planckian Censorship and the Swampland

In this paper, we propose a new Swampland condition, the Trans-Planckian Censorship Conjecture (TCC), based on the idea that in a consistent quantum theory of gravity sub-Planckian quantum fluctuations should remain quantum and never become larger than the Hubble horizon and freeze in an expanding universe. Applied to the case of scalar fields, it leads to conditions that are similar to the refined dS Swampland conjecture. For large field ranges, TCC is stronger than the dS Swampland conjecture but it is weaker for small field ranges. In particular for asymptotic regions of field space, TCC leads to a bound left|V^{prime}right|ge frac{2}{sqrt{left(d-1right)left(d-2right)}}V, which is consistent with all known cases in string theory. Like the dS Swampland conjecture, the TCC forbids long-lived meta-stable dS spaces, but it does allow sufficiently short-lived ones.

The entropic quasi-de Sitter instability time from the distance conjecture

From the entropy argument for the dS swampland conjecture which connects the Gibbons-Hawking entropy bound with the distance conjecture, we find the entropic quasi-dS instability time given by 1/(ϵHH)log⁡(mPl/H) as the lifetime of quasi-dS spacetime. It depends on the slow-roll parameter, and contains the logarithmic factor log⁡(mPl/H) which can be found in the scrambling (or decoherence) time as well. Such a logarithmic factor enhances the geodesic distance of the modulus from the mere Planck scale, and also possibly relaxes the bound on mPl2∇2V/V.

DS spaces and brane worlds in exotic string theories

We investigate string-phenomenological questions of Hull’s exotic superstring theories with Euclidean strings/branes and multiple times. These are known to be plagued by pathologies like the occurrence of ghosts. On the other hand, these theories exhibit de Sitter solutions. Our special focus lies on the question of the coexistence of such de Sitter solutions and ghost-free brane worlds. To this end, the world-sheet CFT description of Euclidean fundamental strings is generalized to include also the open string/D-brane sector. Demanding that in the “observable” gauge theory sector the gauge fields themselves are non-ghosts, a generalization of the dS swampland conjecture is found.

Quantum log-corrections to swampland conjectures

Taking the anti-de Sitter minimum of KKLT and the large volume scenario at face value, we argue for the existence of logarithmic quantum corrections to AdS swampland conjectures. If these conjectures receive such corrections, it is natural to suspect that they also arise for other swampland conjectures, in particular the dS swampland conjecture. We point out that the proposed log-corrections are in accord with the implications of the recently proposed trans-Planckian censorship conjecture. We also comment on the emergence proposal in the context of both perturbative flux models and the KKLT construction.

A Note on the dS Swampland Conjecture, Non‐BPS Branes and K‐Theory

AbstractWe point out that the de Sitter swampland conjecture would be falsified if classical fluxed Type IIA orientifold vacua with a single non‐BPS D7‐brane were indeed part of the string theory landscape. In other words, the dS swampland conjecture implies the cancellation of K‐theory charges on a compact space.

Runaway quintessence, out of the swampland

We propose a simple, well-motivated and robust alternative to a metastable de Sitter vacuum in string theory, consistent with current observations of dark energy and naturally satisfying conjectured swampland constraints. Inflation ends in a supersymmetric Minkowski minimum, with a flat direction that is protected by non-renormalisation theorems. At some scale non-perturbative effects kick in, inducing a runaway scalar potential. The tail of this runaway potential cannot sustain a late-time dominating, slow-roll quintessence. However, the potential always contains a dS maximum. If the modulus starts close to the hilltop, it remains frozen there by Hubble friction for much of the cosmological history, at first sourcing a tiny classical vacuum energy and then constituting a rolling quintessence, with observable consequences. So long as the modulus is localised away from the Standard Model in the extra dimensions, there are no observable fifth forces nor is there time-variation of fundamental constants, and the modulus mass is protected from radiative corrections. We revisit concrete string models based on heterotic orbifold compactifications, and show that their de Sitter extrema satisfy the recently refined dS Swampland Conjecture.