Cosmology

We study the cosmological evolution of an induced gravity model with a self-interacting scalar field $sigma$ and in the presence of matter and radiation. Such model leads to Einstein Gravity plus a cosmological constant as a stable attractor among homogeneous cosmologies and is therefore a viable dark-energy (DE) model for a wide range of scalar field initial conditions and values for its positive $gamma$ coupling to the Ricci curvature $gamma sigma^{2}R$.

The non-commutative kappa-Minkowski field theory, often tauted as a low-energy candidate for the quantum description of gravity, operates on a spacetime which possesses a modified Lorentz invariance, and as such can be probed in high-precision low-energy experiments. We study the first order corrections in kappa to the Standard Model, and show that they typically induce a coupling of nuclear spin to an external background at low energies. Strong limits on this type of interactions push the scale of non-commutativity to more than 10^7 Planck masses, thus exhibiting a severe naturalness problem for kappa-Minkowski Field Theory viewed as an effective description of quantum gravity.

About 20-30 years ago, scientific community was interested in knowing whether dark matter can carry gauge charges. The answer was found to be no. Today, we can ask a similar question: Can dark energy carry gauge charges? The answer this time seems to be yes. We study the possibility that the current accelerated expansion of the universe is driven by the vacuum energy density of a colored scalar field which is responsible for a phase transition in which the gauge SU(3)_c symmetry breaks. If we are stuck in a SU(3)_c - preserving false vacuum, then SU(3)_c symmetry breaking can be accommodated without violating any experimental QCD bounds or bounds from cosmological observations. As a bonus, the model can likely be tested at the LHC. A possible consequence of the model is the existence of fractionally charged massive hadrons. The model can be embedded in supersymmetric theories where massive colored scalar fields appear naturally.

After introduction and motivation, I will present a covariant entropy bound conjecture on dynamical horizon in a general sense. Then I will show its validity in black hole case and cosmological context. Especially its power in constraint on the cosmological constant is addressed. I will end up with the outlook of this conjecture.

A new class of particle physics models of inflation is presented which is based on the phase transition associated with the spontaneous breaking of family symmetry responsible for the generation of the effective quark and lepton Yukawa couplings. We show

We point out that light scalar fields with symmetries generically generate non-Gaussianity in the density fluctuations. Our observation makes the presence of the non-Gaussianity ubiquitous. When the inflationary scale and the properties of the scalar fields satisfy a certain relation, the non-Gaussianity becomes large enough to be observed by the ongoing and planned observations. We name such a particle responsible for a large non-Gaussianity as an \'ungaussiton\', and give explicit examples to realize the ungaussiton mechanism. We also derive a consistency relation between the bispectrum and the trispectrum, tau_NL = 10^3 f_NL^(4/3), which, if confirmed, will strongly support this mechanism.

One of the most compelling hints for physics beyond the standard model is the cosmological observation that nearly a quarter of our universe consists of cold dark matter. In the next few years, LHC shows the promise of producing these elusive particles and possibly measuring their microscopic properties. This will be challenging, per se, and using LHC observations to reconstruct a complete theory of cosmological dark matter could prove quite challenging. In this talk I will discuss the prospects and many challenges facing such a program. In particular, we will consider complications that can arise rather generically from supersymmetry breaking or gravitational effects in the early universe. Although this will make synthesis much more difficult, many of these effects could lead to insights into the baryon asymmetry and its relation to the dark matter abundance.

We formulate a general replica field-theoretic framework for stochastic inflation in which a manifestation of dimensional reduction is found. The scale above which the latter becomes dominant is explicitly calculated. It is found that for a wide class of stochastic systems considerable changes of the spectral index inevitably occur on super-horizon scales. We work out an explicit relation between the noise correlator and the non-Gaussianity parameter $f_{NL}$, which thus can effectively be generated entirely by quantum fluctuations.

We argue that, within a broad class of extensions of the Standard Model, there is a tight corellation between the dynamics of the electroweak phase transition and the cubic self-coupling of the Higgs boson: Models which exhibit a strong first-order electroweak phase transition predict a large deviation of the Higgs self-coupling from the Standard Model prediction, as long as no accidental cancellations occur. Order-one deviations are typical. This shift would be observable at the Large Hadron Collider if the proposed luminosity or energy upgrades are realized, as well as at a future electron-positron collider such as the proposed International Linear Collider. These measurements would provide a laboratory test of the dynamics of the electroweak phase transition.

Loop quantum cosmology is a non-perturbative canonical quantization of simple cosmological models based on loop quantum gravity. In recent years, a greater control on the underlying quantum theory has revealed a picture where the big bang is replaced by a quantum bounce at Planck scale. The evolution across the bounce is unitary and non-singular without a need of choice of exotic potential or matter. By analysis of an exactly solvable model of a homogeneous and isotropic spacetime we will describe how the backward evolution of our universe with the quantum constraint leads to a pre big bang branch. We will also discuss the way it predicts modifications to Friedman dynamics at high curvatures, contrasts with the Wheeler-DeWitt scenario and semi-classicality across the bounce.

I describe a variety of bubbles of nothing which do not require a Kaluza-Klein circle but instead may be found in asymptotically flat or AdS spaces without any identifications.  There are many such bubbles which expand outwards and threaten to destabilize spacetimes with more than four dimensions.   In the AdS case, one can show there are both bubbles and topologically trivial smooth states which violate all of the energy bounds, both classical and quantum, in the corresponding gauge theory.