Related papers: Hidden sector axions: physics and cosmology
We propose a string-inspired model which correlates several aspects of particle physics and cosmology. Inspired by the flat directions and the absence of adjoint Higgs representations found in typical string models, we consider a no-scale…
While axions seem ubiquitous in critical string theories, whether they might survive in any string theoretic description of nature is a difficult question. With some mild assumptions, one can frame the issues in the case that there is an…
The minimal $SO(5)/SO(4)$ linear $\sigma$ model is extended including an additional complex scalar field, singlet under the global $SO(5)$ and the Standard Model gauge symmetries. The presence of this scalar field creates the conditions to…
The Standard Model is the low-energy limit of a microscopic theory which includes extra dimensions and new symmetries. A part of my thesis consisted in constructing a new class of models with two extra dimensions. We showed that these…
A hidden strongly-interacting sector is a possible candidate for dark matter. One scenario consistent with astrophysical constraints is a QCD-like theory with gauge group Sp(4) and two fundamental non-degenerate fermions. We report…
It has been commonly assumed that pseudoscalar contributions to the leptonic decay of charged mesons, like pions and kaons, is strongly constrained due to the helicity suppression present in the ratio $R_{l/l'} = \Gamma(P \rightarrow…
Axions and axion-like particles (ALPs) are a prominent dark matter candidate, drawing motivation in part from the axiverse of string theory. Axion-like particles can also arise as composite degrees of freedom of a dark sector, for example,…
It has recently been conjectured that string theory does not admit de Sitter vacua, and that quintessence explains the current epoch of accelerated cosmic expansion. A proposed, key prediction of this scenario is time-varying couplings in…
The spectrum of stable electrically and magnetically charged supersymmetric particles can change discontinuously as one changes the vacuum on the Coulomb branch of gauge theories with extended supersymmetry in four dimensions. We show that…
Cosmological solutions of the beta function equations for the background fields of the closed bosonic string are investigated at the one-loop level. Following recent work of Kostelecky and Perry, it is assumed that the spatial sections of…
We examine the inter-relationship of the superpotential containing hidden and observable matter fields and the ensuing condensates in free fermionic string models. These gauge and matter condensates of the strongly interacting hidden gauge…
We consider some questions of naturalness which arise when one considers conventional field theories in the presence of gravitation: the problem of global symmetries, the strong CP problem, and the cosmological constant problem. Using…
We compute the action of closed bosonic string field theory at quartic order with fields up to level ten. After level four, the value of the potential at the minimum starts oscillating around a nonzero negative value, in contrast with the…
Confining hidden sectors are an attractive possibility for physics beyond the Standard Model (SM). They are especially motivated by neutral naturalness theories, which reconcile the lightness of the Higgs with the strong constraints on…
The harmonic oscillator in pseudo euclidean space is studied. A straightforward procedure reveals that although such a system may have negative energy, it is stable. In the quantized theory the vacuum state has to be suitably defined and…
A bosonic sector of the four-dimensional low-energy heterotic string theory with two Abelian gauge fields is considered in the stationary case. A new 4X4 unitary null-curvature matrix representation of the theory is derived and the…
In the context of string theory, axions appear to provide the most plausible solution of the strong CP problem. However, as has been known for a long time, in many string-based models, the axion coupling parameter F_a is several orders of…
Dynamical mechanisms to generate an ultralight axion of mass $\sim 10^{-21}-10^{-22}$ eV in supergravity and strings are discussed. An ultralight particle of this mass provides a candidate for dark matter that may play a role for cosmology…
Phantom scalar theories are widely considered in cosmology, but rarely at the quantum level, where they give rise to negative-energy ghost particles. These cause decay of the vacuum into gravitons and photons, violating observational…
We propose a refinement of the physical picture describing different vacua in bosonic string theory. The vacua with closed strings and open strings are connected by the string field theory version of the Higgs mechanism, generalizing the…