A bstract We study the vacua of 4 d heterotic toroidal orbifolds using effective theories consisting an overall Kähler modulus, dilaton, and non-perturbative corrections to both superpotential potential that respect modular invariance. prove three de Sitter no-go theorems for several classes thereby substantiate extend previous conjectures. Additionally, we provide evidence extrema scalar can occur inside PSL(2, ℤ) fundamental domain in contradiction a separate conjecture. also illustrate...

A bstract We consider inflationary models with multiple spectator axions coupled to dark gauge sectors via Chern-Simons (CS) terms. The energy injection into Abelian fields from the engenders a multi-peak profile for scalar and tensor spectra. highlight constraining power of CMB spectral distortions on signal discuss conditions under which can account recently observed stochastic gravitational wave (GW) background in nHz range. Given tantalizing prospect “GW forest” spanning several decades...

We discuss ensemble averages of two-dimensional conformal field theories associated with an arbitrary indefinite lattice integral quadratic form $Q$. provide evidence that the holographic dual after average is three-dimensional Abelian Chern-Simons theory kinetic term determined by The resulting partition function can be written as a modular form, expressed sum over functions on lens spaces. For odd lattices, bulk spin theory, and we identify several novel phenomena in this case. also...

We study the signal and background that arise in nuclear magnetic resonance searches for axion dark matter, finding key differences with existing literature. find spin-precession instruments are much more sensitive than what has been previously estimated a sizable range of masses, sensitivity improvement up to factor 100 using ^{129}Xe sample. This improves detection prospects QCD axion, we estimate experimental requirements reach this motivated target. Our results apply both electric dipole...

A bstract Certain inflationary models can feature periods of preheating — an era preceding reheating during which parametric resonance triggers exponential production bosons. This non-perturbative process have significant impact on the history our universe, with consequences ranging from altered channels to overproduction dark radiation overclosure. In this work, we study axions in string inflation. We find that kinetic couplings and moduli-dependent axion masses give rise generalizations...

We discuss the relations between swampland conjectures and observational constraints on both inflation dark energy. Using requirement $|\ensuremath{\nabla}V|\ensuremath{\ge}cV$, with $c$ as a universal constant whose value can be derived from inflation, there may no observable distinction nonconstant models of However, latest modification above conjecture, which utilizes second derivative potential, opens up opportunity for observations to determine if energy equation state deviates that...

We investigate the possibility that Peccei-Quinn phase transition occurs at a temperature far below symmetry breaking scale. Low temperatures are typical in supersymmetric theories, where fields have small masses. find QCD axions abundantly produced just after transition. The observed dark matter abundance is reproduced even if decay constant much lower than $10^{11}$ GeV. tend to be warm. For some range of constant, effect predicted warmness on structure formation can confirmed by future...

We discuss the interrelations between several ideas in quantum gravity – holography, Swampland, and concept of ensemble averaging. To do so, we study averages Narain-type theories associated with general even quadratic forms their holographic duals. establish emergence global symmetries consistency conjectures forbidding such symmetries. also how spectral decomposition Narain partition functions suggests a natural embedding averaging within low-energy limit certain string compactifications,...

A number of proposed and ongoing experiments search for axion dark matter with a mass nearing the limit set by small scale structure [$\mathcal{O}({10}^{\ensuremath{-}21}\text{ }\text{ }\mathrm{eV})$]. We consider late universe cosmology these models, showing that requiring to have matter-power spectrum matches cold constrains magnitude couplings visible sector. Comparing limits current future experimental efforts, we find many searches require axions an abnormally large coupling Standard...

Similarities between the gauge meditation of supersymmetry breaking and QCD axion model suggest that they originate from same dynamics. We present a class models where Peccei-Quinn symmetry are simultaneously broken. The messengers mediate effects these breakings to Standard Model identical. Since resides in sector, saxion axino heavy. show constraints on decay constant gravitino mass.

We use Pauli–Villars regularization to evaluate the conformal and chiral anomalies in effective field theories from Z3 Z7 compactifications of heterotic string without Wilson lines. show that parameters for multiplets can be chosen such a way anomaly is universal sense its coefficient depends only on single holomorphic function three diagonal moduli. It therefore possible cancel by generalization four-dimensional Green–Schwarz mechanism. In particular we are able reproduce results...

Motivated by closed string perturbation theory arguments S. Shenker, we consider non-perturbative effects of characteristic strength $\mathcal{O}(e^{-1/g_{s}})$, with $g_{s}$ the coupling constant, in supersymmetric critical heterotic theories. We argue that 10D such arise from "D-instantons," i.e. disk diagrams, whose existence relies on a non-trivial interplay between worldsheet and spacetime degrees freedom. In compactifications $\mathrm{SemiSpin}(32)$ string, similar can wrapped...

Certain inflationary models can feature periods of preheating - an era preceding reheating during which parametric resonance triggers exponential production bosons. This non-perturbative process have significant impact on the history our universe, with consequences ranging from altered channels to overproduction dark radiation overclosure. In this work, we study axions in string inflation. We find that kinetic couplings and moduli-dependent axion masses give rise generalizations Mathieu...

We show that a choice of Pauli-Villars regulators allows the cancellation all conformal and chiral anomalies in an effective field theory from Z3 compactification heterotic string with two Wilson lines anomalous U(1).

A bstract The QCD axion can be formulated in a dual description as massive 2-form field. In this picture, the quality problem translates into question if there are additional 3-forms coupled to other than 3-form that emerges at low energy. If such forms exist, resolved via introduction of 2-forms (and thus corresponding axions), one for each 3-form. This motivate an “axiverse from high axion”. work, we discuss issue general case where couples arbitrarily many 3-forms. Given multiple...

We study a class of newly-introduced CFTs associated with even quadratic forms general signature, which we call generalized Narain theories. first summarize the properties these then consider orbifolds theories, thereby obtaining large non-supersymmetric exactly marginal deformations. discuss ensemble averages such theories over their moduli space, and obtain modular form an element discriminant group. The can be written as Poincare series, contains novel invariants lens spaces suggests...

We discuss the prospects of measuring deviations dark energy equation state from w=-1 by using swampland conjectures to relate inflationary models quintessence scenarios. This note is based on work done author with H. Murayama and C. Chiang arXiv:1811.01987.

We discuss interrelations between several ideas in quantum gravity. One is the Swampland program, which states that a low-energy effective field theory should satisfy non-trivial constraints to have an ultraviolet (UV) completion Another concept of ensemble averaging holography, where coarse-grained description obtained by integral over moduli space. To examine relation two, we study averages generalized Narain-type theories associated with general even quadratic form and their holographic...

The QCD axion can be formulated in a dual description as massive 2-form field. In this picture, the quality problem translates into question if there are additional 3-forms coupled to other than 3-form that emerges at low energy. If such forms exist, resolved via introduction of 2-forms (and thus corresponding axions), one for each 3-form. This motivate an "axiverse from high axion". work, we discuss issue general case where couples arbitrarily many 3-forms. Given multiple solution,...

We consider inflationary models with multiple spectator axions coupled to dark gauge sectors via Chern-Simons (CS) terms. The energy injection into Abelian fields from the engenders a multi-peak profile for scalar and tensor spectra. highlight constraining power of CMB spectral distortions on signal discuss conditions under which can account recently observed stochastic gravitational wave (GW) background in nHz range. Given tantalizing prospect ``GW forest'' spanning several decades...

A leading direction in the hunt for axion dark matter is to search its influence on nuclear spins. The detection scheme involves polarizing a sample of nuclei within strong static magnetic field and then looking spin precession induced by oscillating field. We study signal background contributions that arise such experiments (a prominent example being CASPEr), finding key differences with existing literature. Most importantly, limit where transverse spin-relaxation time material largest...

We study the vacua of $4d$ heterotic toroidal orbifolds using effective theories consisting an overall Kähler modulus, dilaton, and non-perturbative corrections to both superpotential potential that respect modular invariance. prove three de Sitter no-go theorems for several classes thereby substantiate extend previous conjectures. Additionally, we provide evidence extrema scalar can occur inside PSL$(2,\mathbb{Z})$ fundamental domain in contradiction a separate conjecture. also illustrate...