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Register a new userOn a boundary-localized Higgs boson in 5D theories
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In the context of a simple five-dimensional (5D) model with bulk matter coupled to a brane-localized Higgs boson, we point out a new non-commutativity in the 4D calculation of the mass spectrum for excited fermion towers: the obtained expression depends on the choice in ordering the limits, N->infinity (infinite Kaluza-Klein tower) and epsilon->0 (epsilon being the parameter introduced for regularizing the Higgs Dirac peak). This introduces the physical question of which one is the correct order; we then show that the two possible orders of regularization (called I and II) are physically equivalent, as both can typically reproduce the measured observables, but that the one with less degrees of freedom (I) could be uniquely excluded by future experimental constraints. This conclusion is based on the exact matching between the 4D and 5D analytical calculations of the mass spectrum - via the regularizations of type I and II. Beyond a deeper insight into the Higgs peak regularizations, this matching also allows us to confirm the validity of the usual 5D mixed-formalism and to clarify the UV cut-off procedure. All the conclusions, deduced from regularizing the Higgs peak through a brane shift or a smoothed square profile, are expected to remain similar in realistic models with a warped extra-dimension.
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We calculate the production and decay rates of the Higgs boson at the LHC in the context of general 5 dimensional (5D) warped scenarios with a spacetime background modified from the usual $AdS_5$, with SM fields propagating in the bulk. We extend previous work by considering the full flavor structure of the SM, and thus including all possible flavor effects coming from mixings with heavy fermions. We proceed in three different ways, first by only including two complete Kaluza-Klein (KK) levels ($15times15$ fermion mass matrices), then including three complete KK levels ($21times21$ fermion mass matrices) and finally we compare with the effect of including the infinite (full) KK towers. We present numerical results for the Higgs production cross section via gluon fusion and Higgs decay branching fractions in both the modified metric scenario and in the usual Randall-Sundrum metric scenario.
We calculate the production rate of the Higgs boson at the LHC in the context of general 5 dimensional (5D) warped scenarios with spacetime background modified from the usual $AdS_5$, and where all the SM fields, including the Higgs, propagate in the bulk. This modification can alleviate considerably the bounds coming from precision electroweak tests and flavor physics. We evaluate the Higgs production rate and show that it is generically consistent with the current experimental results from the LHC for Kaluza-Klein (KK) masses as low as 2 TeV, unlike in pure $AdS_5$ scenarios, where for the same masses, the Higgs production typically receives corrections too large to be consistent with LHC data. Thus the new pressure on warped models arising from LHC Higgs data is also alleviated in $AdS_5$-modified warped scenarios.
A comprehensive, five-dimensional calculation of Higgs-boson production in gluon fusion is performed for both the minimal and the custodially protected Randall-Sundrum (RS) model, with Standard Model fields propagating in the bulk and the scalar sector confined on or near the IR brane. For the first time, an exact expression for the gg->h amplitude in terms of the five-dimensional fermion propagator is derived, which includes the full dependence on the Higgs-boson mass. Various results in the literature are reconciled and shown to correspond to different incarnations of the RS model, in which the Higgs field is either localized on the IR brane or is described in terms of a narrow bulk state. The results in the two scenarios differ in a qualitative way: the gg->h amplitude is suppressed in models where the scalar sector is localized on the IR brane, while it tends to be enhanced in bulk Higgs models. In both cases, effects of higher-dimensional operators contributing to the gg->h amplitude at tree level are shown to be numerically suppressed under reasonable assumptions. There is no smooth cross-over between the two scenarios, since the effective field-theory description breaks down in the transition region. A detailed phenomenological analysis of Higgs production in various RS scenarios is presented, and for each scenario the regions of parameter space already excluded by LHC data are derived.
We argue that the $125 GeV$ Higgs particle is unlikely to arise as a fermion- antifermion composite if the underlying dynamics is a vectorial gauge theory. The reason is that the lightest scalar in such theories is heavier than the lightest pseudo-scalar with the mass difference being fixed by the scale of the theory. LHC searches suggest that the scale of any new physics, including that of a putative new theory dynamically generating the 125 GeV Higgs particle, is relatively high $sim{(1/2TeV-1TeV)}$. Also the LHC analysis suggests that it is {it scalar} namely $J^P = 0^+$ rather than pseudo-scalar. Thus it is unlikely that the Higgs could arise as a composite in such theories- though it will arise in special cases when the underlying binding gauge group is real as a fermion-fermion bound state. The direct considerations of the various two point functions in the large $N_c$ limit presented below- suggest that massless pseudo-scalars, but not any other anomalously light meson, arise as composites of massless fermions say the massless u and $bar{d}$ quarks in QCD. These massless pions manifest the spontaneous breaking of the global axial symmetry in QCD with the pions being (pseudo) Nambu Goldstone Bosons. This offers a different insight into SXSB in QCD and most other confining non-abelian gauge vectorial gauge theory. Specifically we consider the euclidean two point functions $F_I|x-y|$ for asymptotic $|x-y|$ expressed as a sum over fermionic paths. We conjecture that for the pseudo-scalar two point function - and for that case only- self retracing paths and closely related paths make in this limit a positive, coherent and dominant contribution, a contribution which evades the generic asymptotic exponential fall-off and allows the lightest pseudoscalars to be massless. The same arguments imply that the scalars are very massive.
Higgs fields on gauge-natural prolongations of principal bundles are defined by invariant variational problems and related canonical conservation laws along the kernel of a gauge-natural Jacobi morphism.
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