On axionic field ranges, loopholes and the weak gravity conjecture

Brown, Jon; Cottrell, William; Shiu, Gary; Soler, Pablo

doi:10.1007/jhep04(2016)017

Cited by 100 publications

(139 citation statements)

References 25 publications

(98 reference statements)

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“…This is now in perfect agreement with (3.26). 13 Thus, we find that Giddings-Strominger wormholes give rise to an effective potential V (θ) ∼ 2Ke −S cos θ in two independent approaches. We wish to remark that in both approaches we can be agnostic about details of the interpretation of wormholes connecting to baby-universes.…”

Section: Jhep02(2017)097mentioning

confidence: 63%

“…A more careful definition becomes important when several U(1) group factors (or axion species) are present. See [5,9,11,13,17,25] for more details. [113].…”

Section: Gravitational Instantons and The Weak Gravity Conjecturementioning

confidence: 99%

“…Next, we plug in the solution to (2.21), H = n Ar 3 , (E. 13) and restrict ourselves to F (ϕ) = exp(−αϕ)/(3!f 2 ax ), for which we know the analytical solutions:…”

Section: Jhep02(2017)097mentioning

confidence: 99%

See 2 more Smart Citations

Can gravitational instantons really constrain axion inflation?

Hebecker¹,

Mangat²,

Theisen

et al. 2017

J. High Energ. Phys.

100

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Axions play a central role in inflationary model building and other cosmological applications. This is mainly due to their flat potential, which is protected by a global shift symmetry. However, quantum gravity is known to break global symmetries, the crucial effect in the present context being gravitational instantons or Giddings-Strominger wormholes. We attempt to quantify, as model-independently as possible, how large a scalar potential is induced by this general quantum gravity effect. We pay particular attention to the crucial issue which solutions can or cannot be trusted in the presence of a moduli-stabilisation and a Kaluza-Klein scale. An important conclusion is that, due to specific numerical prefactors, the effect is surprisingly small even in UV-completions with the highest possible scale offered by string theory.As we go along, we discuss in detail Euclidean wormholes, cored and extremal instantons, and how the latter arise from 5d Reissner-Nordström black holes. We attempt to dispel possible doubts that wormholes contribute to the scalar potential by an explicit calculation. We analyse the role of stabilised dilaton-like moduli. Finally, we argue that Euclidean wormholes may be the objects satisfying the Weak Gravity Conjecture extended to instantons.

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Section: Jhep02(2017)097mentioning

confidence: 63%

“…A more careful definition becomes important when several U(1) group factors (or axion species) are present. See [5,9,11,13,17,25] for more details. [113].…”

Section: Gravitational Instantons and The Weak Gravity Conjecturementioning

confidence: 99%

See 1 more Smart Citation

Can gravitational instantons really constrain axion inflation?

Hebecker¹,

Mangat²,

Theisen

et al. 2017

J. High Energ. Phys.

100

View full text Add to dashboard Cite

show abstract

“…It was furthermore established in [4][5][6] that scenarios involving multiple axions such as N-flation [7] and alignment [8] would fail to suppress higher instanton corrections assuming instantons which contribute dominantly to the inflationary potential satisfy the WGC. Despite the existence of loopholes, these results create substantial obstacles for many models of axionic inflation and may explain why the thorough investigations of [9,10] have not succeeded in finding a large field model which violates WGC motivated bounds.…”

Section: Jhep10(2016)025mentioning

confidence: 99%

“…For this reason alone, we do not expect a priori to reproduce the tunneling rate for vacuum decay in any limit except for those that reduce to vacuum decay. 6 Second, the theories studied in [20,21] contain only a scalar field, or a scalar field and gravity. In contrast, axion monodromy also contains the 3-form gauge field C 3 .…”

Section: Bounces In Axion Monodromymentioning

confidence: 99%

Tunneling in axion monodromy

Brown

Cottrell

Shiu

et al. 2016

J. High Energ. Phys.

Self Cite

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The Coleman formula for vacuum decay and bubble nucleation has been used to estimate the tunneling rate in models of axion monodromy in recent literature. However, several of Coleman's original assumptions do not hold for such models. Here we derive a new estimate with this in mind using a similar Euclidean procedure. We find that there are significant regions of parameter space for which the tunneling rate in axion monodromy is not well approximated by the Coleman formula. However, there is also a regime relevant to large field inflation in which both estimates parametrically agree. We also briefly comment on the applications of our results to the relaxion scenario.

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What is the magnetic Weak Gravity Conjecture for axions?

Hebecker

Henkenjohann

Witkowski

2017

Fortschritte der Physik

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The electric Weak Gravity Conjecture demands that axions with large decay constant f couple to light instantons. The resulting large instantonic corrections pose problems for natural inflation. We explore an alternative argument based on the magnetic Weak Gravity Conjecture for axions, which we try to make more precise. Roughly speaking, it demands that the minimally charged string coupled to the dual 2‐form‐field exists in the effective theory. Most naively, such large‐f strings curve space too much to exist as static solutions, thus ruling out large‐f axions. More conservatively, one might allow non‐static string solutions to play the role of the required charged objects. In this case, topological inflation would save the superplanckian axion. Furthermore, a large‐f axion may appear in the low‐energy effective theory based on two subplanckian axions in the UV. The resulting effective string is a composite object built from several elementary strings and domain walls. It may or may not satisfy the magnetic Weak Gravity Conjecture depending on how strictly the latter is interpreted and on the cosmological dynamics of this composite object, which remain to be fully understood. Finally, we recall that large‐field brane inflation is naively possible in the codimension‐one case. We show how string‐theoretic back‐reaction closes this apparent loophole of large‐f (non‐periodic) pseudo‐axions.

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On axionic field ranges, loopholes and the weak gravity conjecture

Cited by 100 publications

References 25 publications

Can gravitational instantons really constrain axion inflation?

Can gravitational instantons really constrain axion inflation?

Tunneling in axion monodromy

What is the magnetic Weak Gravity Conjecture for axions?

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