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Register a new userPhase transition and vacuum stability in the classically conformal B-L model
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Within classically conformal models, the spontaneous breaking of scale invariance is usually associated to a strong first order phase transition that results in a gravitational wave background within the reach of future space-based interferometers. In this paper we study the case of the classically conformal gauged B-L model, analysing the impact of this minimal extension of the Standard Model on the dynamics of the electroweak symmetry breaking and derive its gravitational wave signature. Particular attention is paid to the problem of vacuum stability and to the role of the QCD phase transition, which we prove responsible for concluding the symmetry breaking transition in part of the considered parameter space. Finally, we calculate the gravitational wave signal emitted in the process, finding that a large part of the parameter space of the model can be probed by LISA.
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We discuss a classically conformal radiative neutrino model with gauged B$-$L symmetry, in which the B$-$L symmetry breaking can occur through the Coleman-Weinberg mechanism. As a result, Majorana mass term is generated and EW symmetry breaking also occurs. We show some allowed parameters to satisfy several theoretical and experimental constraints. Theoretical constraints are inert conditions and Coleman-Weinberg condition. Experimental bounds are lepton flavor violation(especially mu -> e gamma), the current bound on the $Z$ mass at LHC, in additions to the neutrino oscillations.
An additional $U(1)$ gauge interaction is one of promising extensions of the standard model of particle physics. Among others, the $U(1)_{B-L}$ gauge symmetry is particularly interesting because it addresses the origin of Majorana masses of right-handed neutrinos, which naturally leads to tiny light neutrino masses through the seesaw mechanism. We show that, based on the minimal $U(1)_{B-L}$ model, the symmetry breaking of the extra $U(1)$ gauge symmetry with its minimal Higgs sector in the early Universe can exhibit the first-order phase transition and hence generate a large enough amplitude of stochastic gravitational wave radiation which is detectable in future experiments.
We explore relativistic freeze-in production of scalar dark matter in gauged $B-L$ model, where we focus on the production of dark matter from the decay and annihilation of Standard Model (SM) and $B-L$ Higgs bosons. We consider the Bose-Einstein (BE) and Fermi-Dirac (FD) statistics, along with the thermal mass correction of the SM Higgs boson in our analysis. We show that in addition to the SM Higgs boson, the annihilation and decay of the $B-L$ scalar can also contribute substantially to the dark matter relic density. Potential effects of electroweak symmetry breaking (EWSB) and thermal mass correction in BE framework enhance the dark matter relic substantially as it freezes-in near EWSB temperature via scalar annihilation. However, such effects are not so prominent when the dark matter freezes-in at a later epoch than EWSB, dominantly by decay of scalars. The results of this analysis are rather generic, and applicable to other similar scenarios.
The most general model-independent analysis of the rare $B$ decay, $Bsll$, is presented. There are ten independent local four-Fermi interactions which may contribute to this process. The branching ratio, the forward-backward asymmetry, and the double differential rate are written as functions of the Wilson coefficients of the ten operators. We also study the correlation between the branching ratio and the forward-backward asymmetry by changing each coefficient. This procedure tells us which types of operator contribute to the process, and it will be very useful to pin down new physics systematically, once we have the experimental data with high statistics and the deviation from the Standard Model is found.
We study the Standard Model (SM) in Weyl conformal geometry. This embedding is truly minimal, {it with no new fields} beyond the SM spectrum and Weyl geometry. The action inherits a gauged scale symmetry $D(1)$ (known as Weyl gauge symmetry) from the underlying geometry. The associated Weyl quadratic gravity undergoes spontaneous breaking of $D(1)$ by a geometric Stueckelberg mechanism in which the Weyl gauge field ($omega_mu$) acquires mass by absorbing the spin-zero mode of the $tilde R^2$ term in the action. This mode also generates the Planck scale. The Einstein-Hilbert action emerges in the broken phase. In the presence of the SM, this mechanism receives corrections (from the Higgs) and it can induce electroweak (EW) symmetry breaking. The Higgs field has direct couplings to the Weyl gauge field while the SM fermions only acquire such couplings following the kinetic mixing of the gauge fields of $D(1)times U(1)_Y$. One consequence is that part of the mass of $Z$ boson is not due to the usual Higgs mechanism, but to its mixing with massive $omega_mu$. Precision measurements of $Z$ mass set lower bounds on the mass of $omega_mu$ which can be light (few TeV), depending on the mixing angle and Weyl gauge coupling. The Higgs mass and the EW scale are proportional to the vev of the Stueckelberg field. In the early Universe the Higgs field can have a geometric origin, by Weyl vector fusion, and the Higgs potential can drive inflation. The dependence of the tensor-to-scalar ratio $r$ on the spectral index $n_s$ is similar to that in Starobinsky inflation but mildly shifted to lower $r$ by the Higgs non-minimal coupling to Weyl geometry.
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