James M. Cline

COSMOLOGICAL EXPANSION IN THE PRESENCE OF AN EXTRA DIMENSION

It was recently pointed out that global solutions of Einsteins equations for a 3-brane universe embedded in four spatial dimensions give rise to a Friedmann equation of the form

Update on scalar singlet dark matter

H\ensuremath{\propto}\ensuremath{\rho}

Are inflationary predictions sensitive to very high energy physics

on the brane, instead of the usual

Supersymmetric electroweak baryogenesis

H\ensuremath{\propto}\sqrt{\ensuremath{\rho}}

Inflating in a Better Racetrack

, which is inconsistent with cosmological observations. We remedy this problem by adding cosmological constants to the brane and the bulk, as in the recent scenario of Randall and Sundrum. Our observation allows for normal expansion during nucleosynthesis, but faster than normal expansion in the very early universe, which could be helpful for electroweak baryogenesis, for example.

p-adic Inflation

One of the simplest models of dark matter is where a scalar singlet field S comprises some or all of the dark matter and interacts with the standard model through an vertical bar H vertical bar S-2(2) coupling to the Higgs boson. We update the present limits on the model from LHC searches for invisible Higgs decays, the thermal relic density of S, and dark matter searches via indirect and direct detection. We point out that the currently allowed parameter space is on the verge of being significantly reduced with the next generation of experiments. We discuss the impact of such constraints on possible applications of scalar singlet dark matter, including a strong electroweak phase transition, and the question of vacuum stability of the Higgs potential at high scales.

Loop-generated bounds on changes to the graviton dispersion relation

It has been proposed that the successful inflationary description of density perturbations on cosmological scales is sensitive to the details of physics at extremely high (trans-Planckian) energies. We test this proposal by examining how inflationary predictions depend on higher-energy scales within a simple model where the higher-energy physics is well understood. We find the best of all possible worlds: inflationary predictions are robust against the vast majority of high-energy effects, but can be sensitive to some effects in certain circumstances, in a way which does not violate ordinary notions of decoupling. This implies both that the comparison of inflationary predictions with CMB data is meaningful, and that it is also worth searching for small deviations from the standard results in the hopes of learning about very high energies.

Reheating from Tachyon Condensation

We re-examine the generation of the baryon asymmetry in the minimal supersymmetric standard model (MSSM) during the electroweak phase transition. We find that the dominant source for baryogenesis arises from the chargino sector. The CP-violation comes from the complex phase in the μ parameter, which provides CP-odd contributions to the particle dispersion relations. This leads to different accelerations for particles and antiparticles in the wall region which, combined with diffusion, leads to the separation of higgsinos and their antiparticles in the front of the wall. These asymmetries get transported to produce perturbations in the left-handed chiral quarks, which then drive sphaleron interactions to create the baryon asymmetry. We present a complete derivation of the semiclassical WKB formalism, including the chargino dispersion relations and a self-consistent derivation of the diffusion equations starting from semiclassical Boltzmann equations for WKB-excitations. We stress the advantages of treating the transport equations in terms of the manifestly gauge invariant physical energy and kinetic momentum, rather than in the gauge variant canonical variables used in previous treatments. We show that a large enough baryon asymmetry can be created for the phase of the complex μ-parameter as small as ~ 10−3, which is consistent with bounds from the neutron electric dipole moment.

Supersymmetric electroweak baryogenesis in the WKB approximation

We present a new version of our racetrack inflation scenario which, unlike our original proposal, is based on an explicit compactification of type IIB string theory: the Calabi-Yau manifold 4[1,1,1,6,9]. The axion-dilaton and all complex structure moduli are stabilized by fluxes. The remaining 2 Kahler moduli are stabilized by a nonperturbative superpotential, which has been explicitly computed. For this model we identify situations for which a linear combination of the axionic parts of the two Kahler moduli acts as an inflaton. As in our previous scenario, inflation begins at a saddle point of the scalar potential and proceeds as an eternal topological inflation. For a certain range of inflationary parameters, we obtain the COBE-normalized spectrum of metric perturbations and an inflationary scale of M = 3 × 1014 GeV. We discuss possible changes of parameters of our model and argue that anthropic considerations favor those parameters that lead to a nearly flat spectrum of inflationary perturbations, which in our case is characterized by the spectral index ns = 0.95.

Large non-Gaussianity from non-local inflation

We construct approximate inflationary solutions rolling away from the unstable maximum of p-adic string theory, a nonlocal theory with derivatives of all orders. Novel features include the existence of slow-roll solutions even when the slow-roll parameters, as usually defined, are much greater than unity, as well as the need for the Hubble parameter to exceed the string mass scale m_s. We show that the theory can be compatible with CMB observations if g_s / \sqrt{p} ~ 10^{-7}, where g_s is the string coupling, and if m_s < 10^{-6} M_p. A red-tilted spectrum is predicted, and the scalar-to-tensor ratio is bounded from above as r < 0.006. The p-adic theory is shown to have identical inflationary predictions to a local theory with superPlanckian parameter values, but with the advantage that the p-adic theory is ultraviolet complete.