Standard Model stability bounds for new physics within LHC reach

We analyse the stability lower bounds on the Standard Model Higgs mass by carefully controlling the scale independence of the effective potential. We include resummed leading and next-to-leading-log corrections, and physical pole masses for the Higgs boson, M_H, and the top-quark, M_t. Particular attention is devoted to the cases where the scale of new physics \Lambda is within LHC reach, i.e. \Lambda\leq 10 TeV, which have been the object of recent controversial results. We clarify the origin of discrepancies and confirm our earlier results within the error of our previous estimate. In particular for \Lambda=1 TeV we find that M_H[GeV]>52+0.64(M_t[GeV]-175)-0.50\frac{\alpha_s(M_Z)-0.118}{0.006}. For fixed values of M_t and \alpha_s(M_Z), the error from higher effects, as the lack of exact scale invariance of the effective potential and higher-order radiative corrections, is conservatively estimated to be \simlt 5 GeV.Comment: 17 pages, latex + psfig.sty, 4 figure

Autonomous stochastic resonance in fully frustrated Josephson-junction ladders

We investigate autonomous stochastic resonance in fully frustrated Josephson-junction ladders, which are driven by uniform constant currents. At zero temperature large currents induce oscillations between the two ground states, while for small currents the lattice potential forces the system to remain in one of the two states. At finite temperatures, on the other hand, oscillations between the two states develop even below the critical current; the signal-to-noise ratio is found to display array-enhanced stochastic resonance. It is suggested that such behavior may be observed experimentally through the measurement of the staggered voltage.Comment: 6 pages, 11 figures, to be published in Phys. Rev.

Upper Bounds on the Lightest Higgs Boson Mass in General Supersymmetric Standard Models

In a general supersymmetric standard model there is an upper bound $m_h$ on the tree level mass of the $CP=+1$ lightest Higgs boson which depends on the electroweak scale, $\tan \beta$ and the gauge and Yukawa couplings of the theory. When radiative corrections are included, the allowed region in the $(m_h,m_t)$ plane depends on the scale $\Lambda$, below which the theory remains perturbative, and the supersymmetry breaking scale $\Lambda_s$, that we fix to $1\ TeV$. In the minimal model with $\Lambda=10^{16}\ GeV$: $m_h<130\ GeV$and$m_t<185\ GeV$. In non-minimal models with an arbitrary number of gauge singlets and$\Lambda=10^{16}\ GeV$:$m_h<145\ GeV$and$m_t<185\ GeV$. We also consider supersymmetric standard models with arbitrary Higgs sectors. For models whose couplings saturate the scale$\Lambda=10^{16}\ GeV$we find$m_h<155\ GeV$and$m_t<190\ GeV$. As one pushes the saturation scale$\Lambda$down to$\Lambda_s$, the bounds on$m_h$and$m_t$increase. For instance, in models with$\Lambda=10\ TeV$, the upper bounds for$m_h$and$m_t$go to$415\ GeV$and$385\ GeV$, respectively.Comment: 13 pages, latex, IEM-FT-64/92 (5 postscript figures availables upon request

Higgs Boson Bounds in Three and Four Generation Scenarios

In light of recent experimental results, we present updated bounds on the lightest Higgs boson mass in the Standard Model (SM) and in the Minimal Supersymmetric extension of the Standard Model (MSSM). The vacuum stability lower bound on the pure SM Higgs boson mass when the SM is taken to be valid up to the Planck scale lies above the MSSM lightest Higgs boson mass upper bound for a large amount of SUSY parameter space. If the lightest Higgs boson is detected with a mass M_{H} < 134 GeV (150 GeV) for a top quark mass M_{top} = 172 GeV (179 GeV), it may indicate the existence of a fourth generation of fermions. The region of inconsistency is removed and the MSSM is salvagable for such values of M_{H} if one postulates the existence of a fourth generation of leptons and quarks with isodoublet degenerate masses M_{L} and M_{Q} such that 60 GeV 170 GeV.Comment: 7 pages, 4 figures. To be published in Physical Review

Vacuum Stability Higgs Mass Bound Revisited with Implications for Extra Dimension Theories

We take the standard model to be an effective theory including higher dimensional operators suppressed by scale $\Lambda$ and re-examine the higgs mass bounds from the requirements of vacuum stability. Our results show that the effects of the higher dimensional operators on the higgs mass limits are significant. As an implication of our results, we study the vacuum stability higgs mass bounds in theories with extra dimensions.Comment: Latex, 14 pages, 1 figure. Added references. To appear in Phys. Rev.

Naturalness and theoretical constraints on the Higgs boson mass

Arbitrary regularization dependent parameters in Quantum Field Theory are usually fixed on symmetry or phenomenology grounds. We verify that the quadratically divergent behavior responsible for the lack of naturalness in the Standard Model (SM) is intrinsically arbitrary and regularization dependent. While quadratic divergences are welcome for instance in effective models of low energy QCD, they pose a problem in the SM treated as an effective theory in the Higgs sector. Being the very existence of quadratic divergences a matter of debate, a plausible scenario is to search for a symmetry requirement that could fix the arbitrary coefficient of the leading quadratic behavior to the Higgs boson mass to zero. We show that this is possible employing consistency of scale symmetry breaking by quantum corrections. Besides eliminating a fine-tuning problem and restoring validity of perturbation theory, this requirement allows to construct bounds for the Higgs boson mass in terms of $\delta m^2/m^2_H$ (where $m_H$ is the renormalized Higgs mass and $\delta m^2$ is the 1-loop Higgs mass correction). Whereas $\delta m^2/m^2_H<1$ (perturbative regime) in this scenario allows the Higgs boson mass around the current accepted value, the inclusion of the quadratic divergence demands $\delta m^2/m^2_H$ arbitrarily large to reach that experimental value.Comment: 6 pages, 4 figure

Maximising Social Interactions and Effectiveness within Distance Learning Courses: Cases from Construction

Advanced Internet technologies have revolutionised the delivery of distance learning education. As a result, the physical proximity between learners and the learning providers has become less important. However, whilst the pervasiveness of these technological developments has reached unprecedented levels, critics argue that the student learning experience is still not as effective as conventional face-to-face delivery. In this regard, surveys of distance learning courses reveal that there is often a lack of social interaction attributed to this method of delivery, which tends to leave learners feeling isolated due to a lack of engagement, direction, guidance and support by the tutor. This paper defines and conceptualises this phenomenon by investigating the extent to which distance-learning programmes provide the social interactions of an equivalent traditional classroom setting. In this respect, two distance learning case studies were investigated, covering the UK and Slovenian markets respectively. Research findings identified that delivery success is strongly dependent on the particular context to which the specific distance learning course is designed, structured and augmented. It is therefore recommended that designers of distance learning courses should balance the tensions and nuances associated with commercial viability and pedagogic effectiveness

Supernova Neutrinos, Neutrino Oscillations, and the Mass of the Progenitor Star

We investigate the initial progenitor mass dependence of the early-phase neutrino signal from supernovae taking neutrino oscillations into account. The early-phase analysis has advantages in that it is not affected by the time evolution of the density structure of the star due to shock propagation or whether the remnant is a neutron star or a black hole. The initial mass affects the evolution of the massive star and its presupernova structure, which is important for two reasons when considering the neutrino signal. First, the density profile of the mantle affects the dynamics of neutrino oscillation in supernova. Second, the final iron core structure determines the features of the neutrino burst, i.e., the luminosity and the average energy. We find that both effects are rather small. This is desirable when we try to extract information on neutrino parameters from future supernova-neutrino observations. Although the uncertainty due to the progenitor mass is not small for intermediate $\theta_{13}$ ($10^{-5} \lesssim \sin^{2}{2 \theta_{13}} \lesssim 10^{-3}$), we can, nevertheless, determine the character of the mass hierarchy and whether $\theta_{13}$ is very large or very small.Comment: 8 pages, 15 figure

Renormalization Group Running of Lepton Mixing Parameters in See-Saw Models with S4S_4 Flavor Symmetry

We study the renormalization group running of the tri-bimaximal mixing predicted by the two typical $S_4$ flavor models at leading order. Although the textures of the mass matrices are completely different, the evolution of neutrino mass and mixing parameters is found to display approximately the same pattern. For both normal hierarchy and inverted hierarchy spectrum, the quantum corrections to both atmospheric and reactor neutrino mixing angles are so small that they can be neglected. The evolution of the solar mixing angle $\theta_{12}$ depends on $\tan\beta$ and neutrino mass spectrum, the deviation from its tri-bimaximal value could be large. Taking into account the renormalization group running effect, the neutrino spectrum is constrained by experimental data on $\theta_{12}$ in addition to the self-consistency conditions of the models, and the inverted hierarchy spectrum is disfavored for large $\tan\beta$. The evolution of light-neutrino masses is approximately described by a common scaling factor.Comment: 23 pages, 6figure

Active Brownian Particles. From Individual to Collective Stochastic Dynamics

We review theoretical models of individual motility as well as collective dynamics and pattern formation of active particles. We focus on simple models of active dynamics with a particular emphasis on nonlinear and stochastic dynamics of such self-propelled entities in the framework of statistical mechanics. Examples of such active units in complex physico-chemical and biological systems are chemically powered nano-rods, localized patterns in reaction-diffusion system, motile cells or macroscopic animals. Based on the description of individual motion of point-like active particles by stochastic differential equations, we discuss different velocity-dependent friction functions, the impact of various types of fluctuations and calculate characteristic observables such as stationary velocity distributions or diffusion coefficients. Finally, we consider not only the free and confined individual active dynamics but also different types of interaction between active particles. The resulting collective dynamical behavior of large assemblies and aggregates of active units is discussed and an overview over some recent results on spatiotemporal pattern formation in such systems is given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte