Search

Exotic self-interactions among the Standard Model neutrinos have been proposed as a potential reason behind the tension in the expansion rate, H0, of the universe inferred from different observations. We constrain this proposal using electroweak precision observables, rare meson decays, and neutrinoless double-β decay. In contrast to previous works, we emphasize the importance of carrying out this study in a framework with full Standard Model gauge invariance. We implement this first by working with a relevant set of Standard Model effective field theory operators and subsequently by considering a UV completion in the inverse seesaw model. We find that the scenario in which all flavors of neutrinos self-interact universally is strongly constrained, disfavoring a potential solution to the H0 problem in this case. The scenario with self-interactions only among tau neutrinos is the least constrained and can potentially be consistent with a solution to the H0 problem. [ABSTRACT FROM AUTHOR]

We consider theories with fermionic degrees of freedom that have a fixed point of Wilson-Fisher type in noninteger dimension d=4-2ε. Due to the presence of evanescent operators, i.e., operators that vanish in integer dimensions, these theories contain families of infinitely many operators that can mix with each other under renormalization. We clarify the dependence of the corresponding anomalous-dimension matrix on the choice of renormalization scheme beyond leading order in ε-expansion. In standard choices of scheme, we find that eigenvalues at the fixed point cannot be extracted from a finite-dimensional block. We illustrate in examples a truncation approach to compute the eigenvalues. These are observable scaling dimensions, and, indeed, we find that the dependence on the choice of scheme cancels. As an application, we obtain the IR scaling dimension of four-fermion operators in QED in d=4-2ε at order O(ε²). [ABSTRACT FROM AUTHOR]

We calculate the full two-loop electroweak matching corrections to the operator governing the decay Bq → l+l- in the standard model. Their inclusion removes an electroweak scheme and scale uncertainty of about ±7% of the branching ratio. Using different renormalization schemes of the involved electroweak parameters, we estimate residual perturbative electroweak and QED uncertainties to be less than ±1% at the level of the branching ratio. [ABSTRACT FROM AUTHOR]

The rare K→πννdecays play a central role in testing the standard model and its extensions. Upcoming experiments plan to measure the decay rates with high accuracy. Yet, unknown higher-order electroweak corrections result in a sizeable theory error. We remove this uncertainty by computing the full two-loop electroweak corrections to the top-quark contribution Xt to the rare decays KL→π0νν, K+→π+νν, and B→Xd,sννin the standard model. The remaining theoretical uncertainty related to electroweak effects is now far below 1%. Finally we update the branching ratios to find Br(KL→π0νν)=2.43(39)(6)×10-11 and Br(K+→π+νν)=7.81(75)(29)×10-11. The first error summarizes the parametric, the second the remaining theoretical uncertainties. [ABSTRACT FROM AUTHOR]

We show that a new strongly interacting sector can produce large enhancements of the tt asymmetries at the Tevatron. The Standard Model is extended by a new vectorlike flavor triplet of fermions and one heavy scalar, all charged under a hypercolor gauge group SU(3)HC. This simple extension results in a number of new resonances. The predictions of our model are rather rigid once a small number of UV parameters is fixed, since all the strong dynamics can be directly taken over from our understanding of QCD dynamics. Despite the rather low hypercolor confinement scale of ~100 GeV, the new strongly interacting sector is stealth. It is shielded from present direct and indirect New Physics searches since the light resonances are QCD singlets, whereas the production of the heavier QCD colored resonances leads predominantly to highmultiplicity final states. Improved searches can potentially be devised using top tagged final states or decays into a small number of hypercolor pions. [ABSTRACT FROM AUTHOR]