Naturalness and the Weak Gravity Conjecture

Cheung, Clifford; Remmen, Grant N.

doi:10.1103/physrevlett.113.051601

Cited by 208 publications

(346 citation statements)

References 24 publications

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“…For the smallest black hole with Q 1 = Q 2 = 1, (2.3) gives again M P √ 2g. Notice that the generalized Weak Gravity Conjecture of [57] (see also [21,22]) would have resulted in the more stringent bound M M P g/ √ 2, which as discussed above does not hold. Another way to rephrase the above is that the nondynamical antidiagonal U(1) implements a Z 2 discrete gauge symmetry.…”

Section: Jhep08(2015)032mentioning

confidence: 99%

Transplanckian axions!?

Montero

Uranga

Valenzuela

2015

J. High Energ. Phys.

181

305

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We discuss quantum gravitational effects in Einstein theory coupled to periodic axion scalars to analyze the viability of several proposals to achieve superplanckian axion periods (aka decay constants) and their possible application to large field inflation models. The effects we study correspond to the nucleation of euclidean gravitational instantons charged under the axion, and our results are essentially compatible with (but independent of) the Weak Gravity Conjecture, as follows: single axion theories with superplanckian periods contain gravitational instantons inducing sizable higher harmonics in the axion potential, which spoil superplanckian inflaton field range. A similar result holds for multiaxion models with lattice alignment (like the Kim-Nilles-Peloso model). Finally, theories with N axions can still achieve a moderately superplanckian periodicity (by a √ N factor) with no higher harmonics in the axion potential. The Weak Gravity Conjecture fails to hold in this case due to the absence of some instantons, which are forbidden by a discrete Z N gauge symmetry. Finally we discuss the realization of these instantons as euclidean D-branes in string compactifications.

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Section: Jhep08(2015)032mentioning

confidence: 99%

Transplanckian axions!?

Montero

Uranga

Valenzuela

2015

J. High Energ. Phys.

181

305

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“…We also note that this procedure can be straightforwardly generalised to any p-form in arbitrary dimensions d > p. Moreover, we observe that despite the shift H 3 → H 3 − ig 2 B dθ 0 , the field θ 0 can be kept real (see also [87]). 5 Varying the action in (2.15),…”

Section: Jhep02(2017)097mentioning

confidence: 99%

“…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%

“…In the 4-dimensional theory these moduli appear as scalar fields. Consequently, we will study systems of an axion θ and a scalar ϕ coupled to 5 In other references, e.g. [85,89], the axion field was taken to be imaginary.…”

Section: Gravitational Instantons In the Presence Of A Massless Scalamentioning

confidence: 99%

“…Denote by g (5) M N the RN-metric (2.42), where M, N run over the coordinates of the 4d space and the extra-dimensional coordinate τ . Now, rescale the metric as follows:…”

Section: Interpretation Of the Integration Constant K +mentioning

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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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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Naturalness and the Weak Gravity Conjecture

Cited by 208 publications

References 24 publications

Transplanckian axions!?

Transplanckian axions!?

Can gravitational instantons really constrain axion inflation?

What is the magnetic Weak Gravity Conjecture for axions?

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