119103473
One-loop charge and colour breaking associated with the top Yukawa coupling
We calculate the one-loop contributions to the MSSM effective potential when the scalar top fields have non-zero vacuum expectation values and study their impact on charge and colour breaking bounds.
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.
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).
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.
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.
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.
119263018
Linear growth rate of structure in parametrized post-Friedmannian universes
A possible solution to the dark energy problem is that Einstein's theory of general relativity is modified. A suite of models have been proposed that, in general, are unable to predict the correct amount of large scale structure in the distribution of galaxies or anisotropies in the cosmic microwave background. It has been argued, however, that it should be possible to constrain a general class of theories of modified gravity by focusing on properties such as the growing mode, gravitational slip, and the effective, time-varying Newton's constant. We show that assuming certain physical requirements such as stability, metricity, and gauge invariance, it is possible to come up with consistency conditions between these various parameters. In this paper we focus on theories which have, at most, second derivatives in the metric variables and find restrictions that shed light on current and future experimental constraints without having to resort to a (as yet unknown) complete theory of modified gravity. We claim that future measurements of the growth of structure on small scales (i.e. from $1\char21{}200{h}^{\ensuremath{-}1}\text{ }\text{ }\mathrm{Mpc}$) may lead to tight constraints on both dark energy and modified theories of gravity.
14262164
Mass for Plasma Photons from Gauge Symmetry Breaking
We derive the effective masses for photons in unmagnetized plasma waves using a quantum field theory with two vector fields (gauge fields). In order to properly define the quantum field degrees of freedom we re-derive the classical wave equations on light-front gauge. This is needed because the usual scalar potential of electromagnetism is, in quantum field theory, not a physical degree of freedom that renders negative energy eigenstates. We also consider a background local fluid metric that allows for a covariant treatment of the problem. The different masses for the longitudinal (plasmon) and transverse photons are in our framework due to the local fluid metric. We apply the mechanism of mass generation by gauge symmetry breaking recently proposed by the authors by giving a non-trivial vacuum-expectation-value to the second vector field (gauge field). The Debye length λ D is interpreted as an effective compactification length and we compute an explicit solution for the large gauge transformations that correspond to the specific mass eigenvalues derived here. Using an usual quantum field theory canonical quantization we obtain the usual results in the literature. Although none of these ingredients are new to physicist, as far as the authors are aware it is the first time that such constructions are applied to Plasma Physics. Also we give a physical interpretation (and realization) for the second vector field in terms of the plasma background in terms of known physical phenomena.
15811055
The impact on cosmology of a primordial scaling field
A scalar field with an exponential potential has the particular property that it is attracted into a solution in which its energy scales as the dominant component (radiation or matter) of the Universe, contributing a fixed fraction of the total energy density. We briefly discuss the dynamics of such a scalar field and its impact on Big Bang nucleosynthesis, the growth of large scale structure and abundance of damped Lyman$-\alpha$ systems at high redshift. Given the simplicity of the model, its theoretical motivation, and its success in matching observations, we argue that it should be taken on par with other currently viable models of structure formation.
119362729
Cosmology of a universe with spontaneously broken Lorentz symmetry
A self-consistent effective field theory of modified gravity has recently been proposed with spontaneous breaking of local Lorentz invariance. The symmetry is broken by a vector field with the wrong-sign mass term and it has been shown to have additional graviton modes and modified dispersion relations. In this paper we study the evolution of a homogeneous and isotropic universe in the presence of such a vector field with a minimum lying along the timelike direction. A plethora of different regimes is identified, such as accelerated expansion, loitering, collapse, and tracking.
35321734
Cosmology with a primordial scaling field
A weakly coupled scalar field \ensuremath{\Phi} with a simple exponential potential ${V=M}_{P}^{4}\mathrm{exp}(\ensuremath{-}\ensuremath{\lambda}\ensuremath{\Phi}{/M}_{P})$ where ${M}_{P}$ is the reduced Planck mass, and $\ensuremath{\lambda}g2,$ has an attractor solution in a radiation or matter dominated universe in which it mimics the scaling of the dominant component, contributing a fixed fraction ${\ensuremath{\Omega}}_{\ensuremath{\varphi}}$ (determined by \ensuremath{\lambda}) to the energy density. Such fields arise generically in particle physics theories involving compactified dimensions, with values of \ensuremath{\lambda} which give a cosmologically relevant ${\ensuremath{\Omega}}_{\ensuremath{\varphi}}.$ For natural initial conditions on the scalar field in the early universe the attractor solution is established long before the epoch of structure formation, and in contrast with the solutions used in other scalar field cosmologies, it is one which does not involve an energy scale for the scalar field characteristic of late times. We study in some detail the evolution of matter and radiation perturbations in a standard inflation-motivated $\ensuremath{\Omega}=1$ dark-matter dominated cosmology with this extra field. Using a full Einstein-Boltzmann calculation we compare observable quantities with current data. We find that, for ${\ensuremath{\Omega}}_{\ensuremath{\varphi}}\ensuremath{\simeq}0.08\char21{}0.12,$ these models are consistent with large angle cosmic microwave background anisotropies as detected by COBE, the linear mass variance as compiled from galaxy surveys, big bang nucleosynthesis, the abundance of rich clusters and constraints from the Lyman-\ensuremath{\alpha} systems at high redshift. Given the simplicity of the model, its theoretical motivation and its success in matching observations, we argue that it should be taken on a par with other currently viable models of structure formation.