We consider the effect of a period of inflation with a high energy density upon the stability of the Higgs potential in the early universe. The recent measurement of a large tensor-to-scalar ratio, rT ∼ 0.16, by the BICEP-2 experiment possibly implies that the energy density during inflation was very high, comparable with the GUT scale. Given that the standard model Higgs potential is known to develop an instability at Λ ∼ 10 10 GeV this means that the resulting large quantum fluctuations of the Higgs field could destabilize the vacuum during inflation, even if the Higgs field starts at zero expectation value. We estimate the probability of such a catastrophic destabilisation given such an inflationary scenario and calculate that for a Higgs mass of m h = 125.5 GeV that the top mass must be less than mt ∼ 172 GeV. We present two possible cures: a direct coupling between the Higgs and the inflaton and a non-zero temperature from dissipation during inflation.The discovery of the (Brout-Englert-)Higgs boson of the standard model has rightly been heralded as one of the most significant scientific discoveries of recent years [1,2]. At present there is no evidence to suggest that the particle is anything other than a fundamental scalar field 10 GeV. For this reason there has been much attention paid to the tunneling rate from our vacuum to the unstable vacuum in order to put bounds on the lifetime of our metastable minimum at h = 246 GeV [5][6][7][8][9][10][11].In this letter we will only consider models containing General Relativity and field theory with minimal couplings between the two, in which case the Higgs field acting alone does not seem to be a good inflationary candidate. Nevertheless, since we now know it exists, the behaviour of the Higgs field during inflation has been frequently considered before [12] and since its discovery [13][14][15][16][17][18]. During inflation all fields lighter than the Hubble rate H will receive stochastic quantum fluctuations of order H/2π per Hubble time from the Gibbons-Hawking temperature but scalar fields (and gravitons) in particular can undergo anomalous growth when the wavelength of some Fourier mode exceeds the de Sitter horizon [19]. Since successful inflation with generation of scalar perturbations which fit the data well can be achieved for a wide variety of inflationary energy scales, the magnitude of these quantum fluctuations can be relatively small.Very recently results were presented to the community from the BICEP-2 experiment concerning measurements of the polarisation of the cosmic microwave background radiation [20]. While the results require verification, the observations seem to be most consistent with a tensor-toscalar ratio of around r T = 0.16 +0.06 −0.05 for what they claim is their most realistic dust model. If one chooses to interpret this result as being due to gravitational waves produced during inflation, it immediately sets the scale of the energy density during inflation to be very large, around the GUT scale, 1016 GeV. Under this assumption, th...

We consider a model with a gauge singlet Dirac fermion as a cold dark matter candidate. The dark matter particle communicates with the Standard Model via a gauge singlet scalar mediator that couples to the Higgs. The scalar mediator also serves to create a tree-level barrier in the scalar potential which leads to a strongly first order electroweak phase transition as required for Electroweak Baryogenesis. We find a large number of models that can account for all the dark matter and provide a strong phase transition while avoiding constraints from dark matter direct detection, electroweak precision data, and the latest Higgs data from the LHC. The next generation of direct detection experiments could rule out a large region of the parameter space but can be evaded in some regions when the Higgs-singlet mixing is very small.

A model of high scale inflation is presented where the radial part of the Peccei-Quinn (PQ) field with a non-minimal coupling to gravity plays the role of the inflaton, and the QCD axion is the dark matter. A quantum fluctuation of O(H/2π) in the axion field will result in a smaller angular fluctuation if the PQ field is sitting at a larger radius during inflation than in the vacuum. This changes the effective axion decay constant, fa, during inflation and dramatically reduces the production of isocurvature modes. This mechanism opens up a new window in parameter space where an axion decay constant in the range 10 12 GeV fa 10 15 GeV is compatible with observably large r. The exact range allowed for fa depends on the efficiency of reheating. This model also predicts a minimum possible value of r = 10 −3 . The new window can be explored by a measurement of r possible with Spider and the proposed CASPEr experiment search for high fa axions.

We investigate the possibility of using the only known fundamental scalar, the Higgs, as an inflaton with minimal coupling to gravity. The peculiar appearance of a plateau or a false vacuum in the renormalised effective scalar potential suggests that the Higgs might drive inflation. For the case of a false vacuum we use an additional singlet scalar field, motivated by the strong CP problem, and its coupling to the Higgs to lift the barrier allowing for a graceful exit from inflation by mimicking hybrid inflation. We find that this scenario is incompatible with current measurements of the Higgs mass and the QCD coupling constant and conclude that the Higgs can only be the inflaton in more complicated scenarios. * malcolm.fairbairn@kcl.ac.uk † philipp.grothaus@kcl.ac.uk ‡ robert.hogan@kcl.ac.uk 1 This requirement is to fit the perturbations for N = 60 e-folds before the end of inflation. This model is also in tension with Planck's n S − r plane constraints [1], where n S is the spectral index and r is the tensor-to-scalar ratio 1 arXiv:1403.7483v1 [hep-ph]

We present a new approach to the problem of estimating the redshift of galaxies from photometric data. The approach uses a genetic algorithm combined with non-linear regression to model the 2SLAQ LRG data set with SDSS DR7 photometry. The genetic algorithm explores the very large space of high order polynomials while only requiring optimisation of a small number of terms. We find a σ rms = 0.0408 ± 0.0006 for redshifts in the range 0.4 < z < 0.7. These results are competitive with the current state-of-the-art but can be presented simply as a polynomial which does not require the user to run any code. We demonstrate that the method generalises well to other data sets and redshift ranges by testing it on SDSS DR11 and on simulated data. For other datasets or applications the code has been made available at https://github.com/rbrthogan/GAz.