Assuming the presence of physics beyond the Standard Model (SM) with a characteristic scale M ~ O(10) TeV, we investigate the naturalness of the Higgs sector at scales below M using an effective field theory (EFT) approach. We obtain the leading 1-lo
op EFT contributions to the Higgs mass with a Wilsonian-like hard cutoff, and determine the constraints on the corresponding operator coefficients for these effects to alleviate the little hierarchy problem up to the scale of the effective action Lambda < M, a condition we denote by EFT-naturalness. We also determine the types of physics that can lead to EFT-naturalness and show that these types of new physics are best probed in vector-boson and multiple-Higgs production. The current experimental constraints on these coefficients are also discussed.
We investigate a Randall-Sundrum model with an SU(2) doublet propagating in the bulk. Upon calculating its gravitational effect we find that a stabilized radius can be generated without the use of an additional scalar, as needed for example in the Go
ldberger-Wise (GW) mechanism, and with no additional fine-tuning other than the inescapable one due to the cosmological constant; similar tuning is also present in the GW mechanism. The lowest scalar excitation in this scenario, the counterpart of the radion of the GW mechanism, has both radion-like and Higgs-like couplings to the SM fields. It, thus, plays a dual role and we, therefore, denote it as the Higgs-radion ($h_r$). As opposed to the GW radion case, our Higgs-radion is found to be compatible with the 126 GeV scalar recently discovered at the LHC, at the level of $1sigma$, with a resulting $95%$ CL bound on the KK-gluon mass of: $4.48~TeV<M_{KKG}< 5.44~TeV$. An important consequence of our setup should be accentuated: the radion of the traditional RS scenarios simply does not exist, so that our Higgs-radion is not the conventional mixed state between the GW radion and the Higgs.
Existing models of dynamical electroweak symmetry breaking (EWSB) find it very difficult to get a Higgs of mass lighter than $m_t$. Consequently, in light of the LHC discovery of the ~125 GeV Higgs, such models face a significant obstacle. Moreover,
with three generations those models have a superheavy cut-off around $10^{17}$ GeV, requiring a significant fine-tuning. To overcome these twin difficulties, we propose a hybrid framework for EWSB, in which the Higgs mechanism is combined with a Nambu-Jona-Lasinio mechanism. The model introduces a strongly coupled doublet of heavy quarks with a mass around 500 GeV, which forms a condensate at a compositeness scale $Lambda$ about a few TeV, and an additional unconstrained scalar doublet which behaves as a fundamental doublet at $Lambda$. This fundamental-like doublet has a vanishing quartic term at $Lambda$ and is, therefore, not the SM doublet, but should rather be viewed as a pseudo-Goldstone boson of the underlying strong dynamics. This setup is matched at the compositeness scale $Lambda$ to a tightly constrained hybrid two Higgs doublet model, where both the composite and unconstrained scalars participate in EWSB. This allows us to get a good candidate for the recently observed 125 GeV scalar which has properties very similar to the Standard Model Higgs. The heavier (mostly composite) CP-even scalar has a mass around 500 GeV, while the pseudoscalar and the charged Higgs particles have masses in the range 200 -300 GeV.
In the minimal Standard Model (SM) with four generations (the so called SM4) and in standard two Higgs doublets model (2HDM) setups, e.g., the type II 2HDM with four fermion generations, the contribution of the 4th family heavy leptons to the muon ma
gnetic moment is suppressed and cannot accommodate the measured $ sim 3 sigma$ access with respect to the SM prediction. We show that in a 2HDM for the 4th generation (the 4G2HDM), which we view as a low energy effective theory for dynamical electroweak symmetry breaking, with one of the Higgs doublets coupling only to the 4th family leptons and quarks (thus effectively addressing their large masses), the loop exchanges of the heavy 4th generation neutrino can account for the measured value of the muon anomalous magnetic moment. We also discuss the sensitivity of the lepton flavor violating decays $mu to e gamma$ and $tau to mu gamma$ and of the decay $B_s to mu mu$ to the new couplings which control the muon g-2 in our model.
We consider the possibility that dark matter can communicate with the Standard Model fields via flavor interactions. We take the dark matter to belong to a dark sector which contains at least two types, or flavors, of particles and then hypothesize t
hat the Standard Model fields and dark matter share a common interaction which depends on flavor. As, generically, interaction eigenstates and mass eigenstates need not coincide, we consider both flavor-changing and flavor-conserving interactions. These interactions are then constrained by meson decays, kaon mixing, and current collider bounds, and we examine their relevance for direct detection and LHC.
The possibility of direct detection of light fermionic dark matter in neutrino detectors is explored from a model-independent standpoint. We consider all operators of dimension six or lower which can contribute to the interaction $bar{f} p to e^+ n$,
where $f$ is a dark Majorana or Dirac fermion. Constraints on these operators are then obtained from the $f$ lifetime and its decays which produce visible $gamma$ rays or electrons. We find one operator which would allow $bar{f} p to e^+ n$ at interesting rates in neutrino detectors, as long as $m_f lesssim m_{pi}$. The existing constraints on light dark matter from relic density arguments, supernova cooling rates, and big-bang nucleosynthesis are then reviewed. We calculate the cross-section for $bar{f} p to e^+ n$ in neutrino detectors implied by this operator, and find that Super-K can probe the new physics scale $Lambda$ for this interaction up to ${cal O}(100 {TeV})$
