Monodromy charge in D7-brane inflation

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Springer

Received: January 20, Revised: August 15, Accepted: September 14, Published: October 9,

2020 2020 2020 2020

Manki Kim and Liam McAllister Department of Physics, Cornell University, Ithaca, NY 14853, U.S.A.

E-mail: [email protected], [email protected] Abstract: In axion monodromy inflation, traversing N axion periods corresponds to discharging N units of a quantized charge. In certain models with moving D7-branes, such as Higgs-otic inflation, this monodromy charge is D3-brane charge induced on the D7-branes. The stress-energy of the induced charge affects the internal space, changing the inflaton potential and potentially limiting the field range. We compute the backreaction of induced D3-brane charge in Higgs-otic inflation. The effect on the nonperturbative superpotential is dramatic even for N = 1, and may preclude large-field inflation in this model in the absence of a mechanism to control the backreaction. Keywords: D-branes, Flux compactifications ArXiv ePrint: 1812.03532

c The Authors. Open Access, Article funded by SCOAP3 .

https://doi.org/10.1007/JHEP10(2020)060

JHEP10(2020)060

Monodromy charge in D7-brane inflation

Contents 1

2 Higgs-otic inflation 2.1 Setup 2.2 Magnetized D-brane action 2.3 Inflaton potential from induced charge 2.4 An example 2.5 An issue of orientation

3 3 4 5 6 7

3 Backreaction of monodromy charge 3.1 Perturbative computation of backreaction 3.1.1 Approximation scheme and simplifying assumptions 3.1.2 Perturbed equations of motion 3.1.3 Solution incorporating backreaction 3.2 Effects on Euclidean D3-branes

8 9 10 12 13 14

4 Implications 4.1 Inflaton-dependence of the Pfaffian 4.2 Comment on fluxbrane inflation

15 15 18

5 Conclusions

19

A Conventions for differential forms

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B Green’s function on a toroidal orientifold

23

1

Introduction

Inflationary models involving super-Planckian displacements provide a striking connection between quantum gravity and observable phenomena. Upper limits on primordial B-mode polarization in the CMB have excluded some models of large-field inflation, but others remain viable [1]. At the same time, the theoretical question of the status of super-Planckian displacements in quantum gravity remains unresolved, despite much activity. Large-field inflation is readily described in effective field theory, but crucially relies on assumptions about symmetries in quantum gravity. A prototypical example is the shift symmetry of an axion with decay constant f  Mpl [2]. No assumption about quantum gravity that is sufficient to protect large-field inflation has yet been put on indisputably solid footing in string theory: on the contrary, general expectations about the destruction of global symmetry charges by black holes, as well as conjectures about Weak Gravity and

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1 Introduction

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about moduli spaces in quantum gravity [3, 4], suggest that controlling a super-Planckian displacement in a quantum gravity theory is difficult. In view of these results, ignoring the problem of ultravio