18094761
Vacuum Stability in two-Higgs doublet models
In this work we review the status of tree-level vacuum stability in general two-Higgs doublet models. We also discuss the problem of Normal minima in some classes of potentials. In some of these potentials, Normal minima can coexist leading to potentially dangerous physic scenarios as, for instance, a two step spontaneous symmetry breaking.
119493491
One-loop stau masses in the effective potential approach
We calculate the one-loop contributions to the tau slepton masses in the Minimal Supersymmetric Standard Model in the effective potential approach. For the majority of parameter space under study, those corrections are shown to elevate the value of the lightest stau mass.
118589050
Avoiding Death by Vacuum
The two-Higgs doublet model (2HDM) can have two electroweak breaking, CP-conserving, minima. The possibility arises that the minimum which corresponds to the known elementary particle spectrum is metastable, a possibility we call the panic vacuum. We present analytical bounds on the parameters of the softly broken Peccei-Quinn 2HDM which are necessary and sufficient conditions to avoid this possibility. We also show that, for this particular model, the current LHC data already tell us that we are necessarily in the global minimum of the theory, regardless of any cosmological considerations about the lifetime of the false vacua.
119180593
Metastability bounds on the two Higgs doublet model
A bstractIn the two Higgs doublet model, there is the possibility that the vacuum where the universe resides in is metastable. We present the tree-level bounds on the scalar potential parameters which have to be obeyed to prevent that situation. Analytical expressions for those bounds are shown for the most used potential, that with a softly broken Z2 symmetry. The impact of those bounds on the model’s phenomenology is discussed in detail, as well as the importance of the current LHC results in determining whether the vacuum we live in is or is not stable. We demonstrate how the vacuum stability bounds can be obtained for the most generic CP-conserving potential, and provide a simple method to implement them.
118483060
Can we build a sensible theory with broken charge and colour symmetries
Charge and colour symmetries are broken using the vevs of scalar fields, but it is shown the theory possesses a photon-like massless particle and electroweak interactions almost identical to those of the Standard Model. We consider experimental signatures of this theory.
18964730
Probing wrong-sign Yukawa couplings at the LHC and a future linear collider
We consider the two-Higgs-doublet model as a framework in which to evaluate the viability of scenarios in which the sign of the coupling of the observed Higgs boson to down-type fermions (in particular, b-quark pairs) is opposite to that of the Standard Model (SM), while at the same time all other tree-level couplings are close to the SM values. We show that, whereas such a scenario is consistent with current LHC observations, both future running at the LHC and a future e +e − linear collider could determine the sign of the Higgs coupling to b-quark pairs. Discrimination is possible for two reasons. First, the interference between the b-quark and the t-quark loop contributions to the ggh coupling changes sign. Second, the charged-Higgs loop contribution to the γγh coupling is large and fairly constant up to the largest charged-Higgs mass allowed by tree-level unitarity bounds when the b-quark Yukawa coupling has the opposite sign from that of the SM (the change in sign of the interference terms between the b-quark loop and the W and t loops having negligible impact).
119258154
Modified Gravity and Cosmology
Abstract In this review we present a thoroughly comprehensive survey of recent work on modified theories of gravity and their cosmological consequences. Amongst other things, we cover General Relativity, scalar–tensor, Einstein–aether, and Bimetric theories, as well as TeVeS, f ( R ) , general higher-order theories, Hořava–Lifschitz gravity, Galileons, Ghost Condensates, and models of extra dimensions including Kaluza–Klein, Randall–Sundrum, DGP, and higher co-dimension braneworlds. We also review attempts to construct a Parameterised Post-Friedmannian formalism, that can be used to constrain deviations from General Relativity in cosmology, and that is suitable for comparison with data on the largest scales. These subjects have been intensively studied over the past decade, largely motivated by rapid progress in the field of observational cosmology that now allows, for the first time, precision tests of fundamental physics on the scale of the observable Universe. The purpose of this review is to provide a reference tool for researchers and students in cosmology and gravitational physics, as well as a self-contained, comprehensive and up-to-date introduction to the subject as a whole.
16319433
The trispectrum of the cosmic microwave background on subdegree angular scales: an analysis of the BOOMERanG data
The trispectrum of the cosmic microwave background can be used to assess the level of non-Gaussianity on cosmological scales. It probes the fourth-order moment, as a function of angular scale, of the probability distribution function of fluctuations and has been shown to be sensitive to primordial non-Gaussianity, secondary anisotropies (such as the Ostriker–Vishniac effect) and systematic effects (such as astrophysical foregrounds). In this paper we develop a formalism for estimating the trispectrum from high-resolution sky maps that incorporates the impact of finite sky coverage. This leads to a series of operations applied to the data set to minimize the effects of contamination due to the Gaussian component and correlations between estimates at different scales. To illustrate the effect of the estimation process, we apply our procedure to the BOOMERanG data set and show that it is consistent with Gaussianity. This work presents the first estimation of the cosmic microwave background trispectrum on subdegree scales.
19317675
Tensor interpretation of BICEP2 results severely constrains axion dark matter.
The recent detection of B modes by the BICEP2 experiment has nontrivial implications for axion dark matter implied by combining the tensor interpretation with isocurvature constraints from Planck observations. In this Letter the measurement is taken as fact, and its implications considered, though further experimental verification is required. In the simplest inflation models, r=0.2 implies HI=1.1×10(14)  GeV. If the axion decay constant fa1 accounts for theoretical uncertainty). If fa>HI/2π then vacuum fluctuations of the axion field place conflicting demands on axion DM: isocurvature constraints require a DM abundance which is too small to be reached when the backreaction of fluctuations is included. High-fa QCD axions are thus ruled out. Constraints on axionlike particles, as a function of their mass and DM fraction, are also considered. For heavy axions with ma≳10(-22)  eV we find Ωa/Ωd≲10(-3), with stronger constraints on heavier axions. Lighter axions, however, are allowed and (inflationary) model-independent constraints from the CMB temperature power spectrum and large scale structure are stronger than those implied by tensor modes.
119235213
Ricci focusing, shearing, and the expansion rate in an almost homogeneous Universe
The Universe is inhomogeneous, and yet it seems to be incredibly well-characterised by a homogeneous relativistic model. One of the current challenges is to accurately characterise the properties of such a model. In this paper we explore how inhomogeneities may affect the overall optical properties of the Universe by quantifying how they can bias the redshift-distance relation in a number of toy models that mimic the real Universe. The models that we explore are statistically homogeneous on large scales. We find that the effect of inhomogeneities is of order of a few percent, which can be quite important in precise estimation of cosmological parameters. We discuss what lessons can be learned to help us tackle a more realistic inhomogeneous universe.
15105689
Effective Electric and Magnetic Local Actions for Electromagnetism with two Gauge Fields
A simple mechanism of dynamical symmetry breaking of electromagnetism with two gauge fields (U(1) × U(1)) is considered. By considering the action variations with respect to the gauge connections F = dA and G = dC we obtain an electric and a magnetic effective actions (U(1)) that have an extra coupling to the magnetic and electric currents (respectivelly) that decouple from the classical theory, meaning that it does not contribute to the standard equations of motion obtained by varying A and C, i.e. Maxwell equations. The extra gauge field C(or A) effectivelly is fixed by the physical effective field A(or C) constituting a non-trivial configuration C = C(A) (or A = A(C)) such that the field discontinuities (Dirac string or WuYang non-trivial fiber-bundle) are encoded in the extra gauge field C (or A). Our construction is only compactible with local current densities. work supported by SFRH/BPD/17683/2004 and POCTI P-FIS-57547/2004; also at Centra