https://biblio.ugent.be/publication/685594/file/1130605.pdf

Review of Particle Physics

We review in detail a number of approaches that have been adopted to try and explain the remarkable observation of our accelerating universe. In particular we discuss the arguments for and recent progress made towards understanding the nature of dark energy. We review the observational evidence for the current accelerated expansion of the universe and present a number of dark energy models in addition to the conventional cosmological constant, paying particular attention to scalar field models such as quintessence, K-essence, tachyon, phantom and dilatonic models. The importance of cosmological scaling solutions is emphasized when studying the dynamical system of scalar fields including coupled dark energy. We study the evolution of cosmological perturbations allowing us to confront them with the observation of the Cosmic Microwave Background and Large Scale Structure and demonstrate how it is possible in principle to reconstruct the equation of state of dark energy by also using Supernovae Ia observational data. We also discuss in detail the nature of tracking solutions in cosmology, particle physics and braneworld models of dark energy, the nature of possible future singularities, the effect of higher order curvature terms to avoid a Big Rip singularity, and approaches to modifying gravity which leads to a late-time accelerated expansion without recourse to a new form of dark energy.

Dynamics of dark energy

http://risa.stanford.edu/teaching/362/particledarkmatter.pdf

Particle dark matter: Evidence, candidates and constraints

This paper describes the ATLAS experiment as installed in i ts experimental cavern at point 1 at CERN. It also presents a brief overview of the expec ted performance of the detector.

http://absimage.aps.org/image/SES08/MWS_SES08-2008-020010.pdf

The ATLAS Experiment at the CERN Large Hadron Collider

This is a review of the physics and cosmology of the cosmological constant. Focusing on recent developments, I present a pedagogical overview of cosmology in the presence of a cosmological constant, observational constraints on its magnitude, and the physics of a small (and potentially nonzero) vacuum energy.

/pdf/the-cosmological-constant-4ljm1nl1cq.pdf

The Cosmological Constant

Soft supersymmetry breaking in KKLT flux compactification

We extend the KKLT approach to moduli stabilization by including the dilaton and the complex structure moduli into the effective supergravity theory. Decoupling of the dilaton is neither always possible nor necessary for the existence of stable minima with zero (or positive) cosmological constant. The pattern of supersymmetry breaking can be much richer than in the decoupling scenario of KKLT.

Stability of flux compactifications and the pattern of supersymmetry breaking

We discuss a scheme to implement the relaxion solution to the hierarchy problem with multiple axions, and present a UV-completed model realizing the scheme. All of the N axions in our model are periodic with a similar decay constant f well below the Planck scale. In the limit N ≫ 1, the relaxion ϕ corresponds to an exponentially long multi-helical flat direction which is shaped by a series of mass mixing between nearby axions in the compact field space of N axions. With the length of flat direction given by Δϕ = 2πf
 eff ∼ e
 ξN
 f for $$ \xi = \mathcal{O}(1) $$
 , both the scalar potential driving the evolution of φ during the inflationary epoch and the ϕ-dependent Higgs boson mass vary with an exponentially large periodicity of $$ \mathcal{O}\left({f}_{\mathrm{eff}}\right) $$
 , while the back reaction potential stabilizing the relaxion has a periodicity of $$ \mathcal{O}(f) $$
 . A natural UV completion of our scheme can be found in high scale or (mini) split supersymmetry (SUSY) scenario with the axion scales generated by SUSY breaking as $$ f\sim \sqrt{m_{\mathrm{SUSY}}{M}_{\ast }} $$
 , where the soft SUSY breaking scalar mass m
 SUSY can be well above the weak scale, and the fundamental scale M
 * can be identified as the Planck scale or the GUT scale.

/pdf/realizing-the-relaxion-from-multiple-axions-and-its-uv-45fg83zvwi.pdf

Realizing the relaxion from multiple axions and its UV completion with high scale supersymmetry

In some string compactifications, for instance the recently proposed KKLT set-up, light moduli are stabilized by nonperturbative effects at supersymmetric AdS vacuum which is lifted to a dS vacuum by supersymmetry breaking uplifting potential. In such models, soft supersymmetry breaking terms are determined by a specific mixed modulus-anomaly mediation in which the two mediations typically give comparable contributions to soft parameters. Similar pattern of soft terms can arise also in brane models to stabilize the radion by nonperturbative effects. We examine some phenomenological consequences of this mixed modulus-anomaly mediation, including the pattern of low energy sparticle spectrum and the possibility of electroweak symmetry breaking. It is noted that adding the anomaly-mediated contributions at MGUT amounts to replacing the messenger scale of the modulus mediation by a mirage messenger scale (m3/2/MPl)?/2MGUT where ? = m3/2/[M0ln (MPl/m3/2)] for M0 denoting the modulus-mediated contribution to the gaugino mass at MGUT. The minimal KKLT set-up predicts ? = 1. As a consequence, for ? = (1), the model can lead to a highly distinctive pattern of sparticle masses at TeV scale, particularly when ? = 2.

https://iopscience.iop.org/article/10.1088/1126-6708/2005/09/039/pdf

Phenomenology of mixed modulus-anomaly mediation in fluxed string compactifications and brane models

We extend the Kim-Nilles-Peloso (KNP) alignment mechanism for natural inflation to models with $Ng2$ axions, which obtains super-Planckian effective axion decay constant ${f}_{\text{eff}}\ensuremath{\gg}{M}_{\mathrm{Pl}}$ through an alignment of the anomaly coefficients of multiple axions having sub-Planckian fundamental decay constants ${f}_{0}\ensuremath{\ll}{M}_{\mathrm{Pl}}$. The original version of the KNP mechanism realized with two axions requires that some of the anomaly coefficients should be of the order of ${f}_{\text{eff}}/{f}_{0}$, which would be uncomfortably large if ${f}_{\text{eff}}/{f}_{0}\ensuremath{\gtrsim}\mathcal{O}(100)$ as suggested by the recent BICEP2 results. We note that the KNP mechanism can be realized with the anomaly coefficients of $\mathcal{O}(1)$ if the number of axions $N$ is large as $N\mathrm{ln}N\ensuremath{\gtrsim}2\mathrm{ln}({f}_{\text{eff}}/{f}_{0})$, in which case the effective decay constant can be enhanced as ${f}_{\text{eff}}/{f}_{0}\ensuremath{\sim}\sqrt{N!}{n}^{N\ensuremath{-}1}$ for $n$ denoting the typical size of the integer-valued anomaly coefficients. Comparing to the other multiple axion scenario, the $N$-flation scenario which requires $N\ensuremath{\sim}{f}_{\text{eff}}^{2}/{f}_{0}^{2}$, the KNP mechanism has a virtue of not invoking to a too large number of axions, although it requires a specific alignment of the anomaly coefficients, which can be achieved with a probability of $\mathcal{O}({f}_{0}/{f}_{\text{eff}})$ under a random choice of the anomaly coefficients. We also present a simple model realizing a multiple axion monodromy along the inflaton direction.

Kiwoon Choi

Papers

Soft supersymmetry breaking in KKLT flux compactification

Stability of flux compactifications and the pattern of supersymmetry breaking

Realizing the relaxion from multiple axions and its UV completion with high scale supersymmetry

Phenomenology of mixed modulus-anomaly mediation in fluxed string compactifications and brane models

Natural inflation with multiple sub-Planckian axions