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We explore the possibility that scale symmetry is a quantum symmetry that is broken only spontaneously and apply this idea to the Standard Model (SM). We compute the quantum corrections to the potential of the higgs field ($phi$) in the classically scale invariant version of the SM ($m_phi=0$ at tree level) extended by the dilaton ($sigma$). The tree-level potential of $phi$ and $sigma$, dictated by scale invariance, may contain non-polynomial effective operators, e.g. $phi^6/sigma^2$, $phi^8/sigma^4$, $phi^{10}/sigma^6$, etc. The one-loop scalar potential is scale invariant, since the loop calculations manifestly preserve the scale symmetry, with the DR subtraction scale $mu$ generated spontaneously by the dilaton vev $musimlanglesigmarangle$. The Callan-Symanzik equation of the potential is verified in the presence of the gauge, Yukawa and the non-polynomial operators. The couplings of the non-polynomial operators have non-zero beta functions that we can actually compute from the quantum potential. At the quantum level the higgs mass is protected by spontaneously broken scale symmetry, even though the theory is non-renormalizable. We compare the one-loop potential to its counterpart computed in the traditional DR scheme that breaks scale symmetry explicitly ($mu=$constant) in the presence at the tree level of the non-polynomial operators.
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We consider the static potential in theories exhibiting spontaneous symmetry breaking. We use our findings to calculate the static potential of the Standard Model at one-loop order. We do so in both the Wilson loop and scattering amplitude approaches and discuss the limitations of the Wilson loop approach. As the field content of the SM is extensive, analogous results to ours in a large set of models is now achievable by varying the appropriate couplings and group theory factors.
We discuss renormalization in a toy model with one fermion field and one real scalar field phi, featuring a spontaneously broken discrete symmetry which forbids a fermion mass term and a phi^3 term in the Lagrangian. We employ a renormalization scheme which uses the MSbar scheme for the Yukawa and quartic scalar couplings and renormalizes the vacuum expectation value of phi by requiring that the one-point function of the shifted field is zero. In this scheme, the tadpole contributions to the fermion and scalar selfenergies are canceled by choice of the renormalization parameter delta_v of the vacuum expectation value. However, delta_v and, therefore, the tadpole contributions reenter the scheme via the mass renormalization of the scalar, in which place they are indispensable for obtaining finiteness. We emphasize that the above renormalization scheme provides a clear formulation of the hierarchy problem and allows a straightforward generalization to an arbitrary number of fermion and scalar fields.
We present a model for describing nuclear matter at finite density based on quarks interacting with chiral fields, sigma and pi and with vector mesons introduced as massive gauge fields. The chiral Lagrangian includes a logarithmic potential, associated with the breaking of scale invariance. We provide results for the soliton in vacuum and at finite density, using the Wigner-Seitz approximation. We show that the model can reach higher densities respect to the linear-sigma model and that the introduction of vector mesons allows to obtain saturation. This result was never obtained before in similar approaches.
Calculations of high multiplicity Higgs amplitudes exhibit a rapid growth that may signal an end of perturbative behavior or even the need for new physics phenomena. As a step towards this problem we consider the quantum mechanical equivalent of $1 to n$ scattering amplitudes in a spontaneously broken $phi^4$-theory by extending our previous results on the quartic oscillator with a single minimum to transitions $langle n lvert hat{x} rvert 0 rangle$ in the symmetric double-well potential with quartic coupling $lambda$. Using recursive techniques to high order in perturbation theory, we argue that these transitions are of exponential form $langle n lvert hat{x} rvert 0 rangle sim exp left( F (lambda n) / lambda right)$ in the limit of large $n$ and $lambda n$ fixed. We apply the methods of exact perturbation theory put forward by Serone et al. to obtain the exponent $F$ and investigate its structure in the regime where tree-level perturbation theory violates unitarity constraints. We find that the resummed exponent is in agreement with unitarity and rigorous bounds derived by Bachas.
The Ward identities involving the currents associated to the spontaneously broken scale and special conformal transformations are derived and used to determine, through linear order in the two soft-dilaton momenta, the double-soft behavior of scattering amplitudes involving two soft dilatons and any number of other particles. It turns out that the double-soft behavior is equivalent to performing two single-soft limits one after the other. We confirm the new double-soft theorem perturbatively at tree-level in a $D$-dimensional conformal field theory model, as well as nonperturbatively by using the gravity dual of ${cal{N}}=4$ super Yang-Mills on the Coulomb branch; i.e. the Dirac-Born-Infeld action on AdS${}_5 times S^5$.
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