arXiv subjects

J. Cline

Publications and source records attributed to J. Cline.

9 recordsLinked to original sources

arXiv2003

Decoupling, Trans-Planckia and Inflation

We survey recent calculations probing what constraints decoupling can put on the influence of very-high-energy physics on the predictions of inflation for the cosmic microwave background. Using garden-variety hybrid inflation models we identify two ways in which higher-energy physics can intrude into inflationary predictions. 1. Non-adiabatic physics up to 30 e-foldings before horizon exit can have observable consequences for the CMB, including the introduction of features in the fluctuation spectrum at specific multipoles and a general suppression of power at large scales (a prediction which was made before the recent release of WMAP results). Our comparison of simple models with the data marginally improves the goodness of fit compared to the standard concordance cosmology, but only at the 1.5-sigma level. 2. Adiabatic physics can also affect inflationary predictions through virtual loops of very-heavy particles, but these can only be distinguished from lower-energy effects within the context of specific models. We believe our conclusions should apply equally well to trans-Planckian physics provided only that this physics satisfies decoupling, such as string theory appears to do. (Non-decoupling trans-Planckian proposals must explain why meaningful theoretical predictions at low energies are possible at all.)

astro-ph↗

arXiv2003

Effective Field Theories and Inflation

We investigate the possible influence of very-high-energy physics on inflationary predictions focussing on whether effective field theories can allow effects which are parametrically larger than order H^2/M^2, where M is the scale of heavy physics and H is the Hubble scale at horizon exit. By investigating supersymmetric hybrid inflation models, we show that decoupling does not preclude heavy-physics having effects for the CMB with observable size even if H^2/M^2 << O(1%), although their presence can only be inferred from observations given some a priori assumptions about the inflationary mechanism. Our analysis differs from the results of hep-th/0210233, in which other kinds of heavy-physics effects were found which could alter inflationary predictions for CMB fluctuations, inasmuch as the heavy-physics can be integrated out here to produce an effective field theory description of low-energy physics. We argue, as in hep-th/0210233, that the potential presence of heavy-physics effects in the CMB does not alter the predictions of inflation for generic models, but does make the search for deviations from standard predictions worthwhile.

hep-th↗

arXiv2003

Leptogenesis with Left-Right domain walls

The presence of domain walls separating regions of unbroken $SU(2)_L$ and $SU(2)_R$ is shown to provide necessary conditions for leptogenesis which converts later to the observed Baryon aymmetry. The strength of lepton number violation is related to the majorana neutrino mass and hence related to current bounds on light neutrino masses. Thus the observed neutrino masses and the Baryon asymmetry can be used to constrain the scale of Left-Right symmetry breaking.

hep-ph↗

arXiv2002

Loop-Generated Bounds on Changes to the Graviton Dispersion Relation

We identify the effective theory appropriate to the propagation of massless bulk fields in brane-world scenarios, to show that the dominant low-energy effect of asymmetric warping in the bulk is to modify the dispersion relation of the effective 4-dimensional modes. We show how such changes to the graviton dispersion relation may be bounded through the effects they imply, through loops, for the propagation of standard model particles. We compute these bounds and show that they provide, in some cases, the strongest constraints on nonstandard gravitational dispersions. The bounds obtained in this way are the strongest for the fewest extra dimensions and when the extra-dimensional Planck mass is the smallest. Although the best bounds come for warped 5-D scenarios, for which the 5D Planck Mass is O(TeV), even in 4 dimensions the graviton loop can lead to a bound on the graviton speed which is comparable with other constraints.

hep-ph↗

arXiv2000

Supergravity Inspired Warped Compactifications and Effective Cosmological Constants

We propose a supergravity inspired derivation of a Randall-Sundrum's type action as an effective description of the dynamics of a brane coupled to the bulk through gravity only. The cosmological constants in the bulk and on the brane appear at the classical level when solving the equations of motion describing the bosonic sector of supergravities in ten and eleven dimensions coupled to the brane. They are related to physical quantities like the brane electric charge and thus inherit some of their physical properties. The most appealing property is their quantization: in d_\perp extra dimensions, Lambda_brane goes like N and Lambda_bulk like N^{2/(2-d_perp)}. This dynamical origin also explains the apparent fine-tuning required in the Randall-Sundrum scenario. In our approach, the cosmological constants are derived parameters and cannot be chosen arbitrarily; instead they are determined by the underlying Lagrangian. Some of the branes we construct that support cosmological constant in the bulk have supersymmetric properties: D3-branes of type IIB superstring theory provide an explicit example.

hep-th↗

arXiv1999

Inflating Intersecting Branes and Remarks on the Hierarchy Problem

We generalize solutions of Einstein's equations for intersecting branes in higher dimensional spacetimes to the nonstatic case, modeling an expanding universe. The relation between the Hubble rate, the brane tensions, and the bulk cosmological constant is similar to the case of a single 3-brane in a 5-dimensional spacetime. However, because the bulk inflates as well as the branes, this class of solutions suffers from Newton's constant tending toward zero on the TeV brane, where the Randall-Sundrum mechanism should solve the weak scale hierarchy problem. The strength of gravity remains constant on the Planck brane, however.

hep-ph↗

arXiv1998

Electromagnetic Response and Approximate SO(5) Symmetry in High-Tc Superconductors

It has been proposed that the effective Hamiltonian describing high T_c superconductivity in cuprate materials has an approximate SO(5) symmetry relating the superconducting (SC) and antiferromagnetic (AF) phases of these systems. We show that robust consequences of this proposal are potentially large optical conductivities and Raman scattering rates in the AF phase, due to the electromagnetic response of the doubly-charged pseudo Goldstone bosons which must exist there. This provides strong constraints on the properties of the bosons, such as their mass gap and velocity.

cond-mat.supr-con↗

arXiv1998

Supersymmetric Electroweak Baryogenesis in the WKB approximation

We calculate the baryon asymmetry generated at the electroweak phase transition in the minimal supersymmetric standard model, treating the particles in a WKB approximation in the bubble wall background. A set of diffusion equations for the particle species relevant to baryon generation, including source terms arising from the CP violation associated with the complex phase $δ$ of the $μ$ parameter, are derived from Boltzmann equations, and solved. The conclusion is that $δ$ must be $\gsim 0.1$ to generate a baryon asymmetry consistent with nucleosynthesis. We compare our results to several other recent computations of the effect, arguing that some are overestimates.

hep-ph↗

arXiv1992

A Natural Framework for Solar and 17 keV Neutrinos

Motivated by recent experimental claims for the existence of a 17 keV neutrino and by the solar neutrino problem, we construct a class of models which contain in their low-energy spectrum a single light sterile neutrino and one or more Nambu-Goldstone bosons. In these models the required pattern of breaking of lepton-number symmetry takes place near the electroweak scale and all mass heirarchies are technically natural. The models are compatible with all cosmological and astrophysical constraints, and can solve the solar neutrino problem via either the MSW effect or vacuum oscillations. The deficit in atmospheric muon neutrinos seen in the Kamiokande and IMB detectors can also be explained in these models.

hep-ph↗