SM Higgs mass bounds from theory

The two-loop Higgs mass upper bounds are reanalyzed. Previous results for a cutoff scale $\Lambda\approx$ few TeV are found to be too stringent. For $\Lambda=10^{19}$ GeV we find $M_H < 180 \pm 4\pm 5$ GeV, the first error indicating the theoretical uncertainty, the second error reflecting the experimental uncertainty due to $m_t = 175 \pm 6$ GeV. We also summarize the lower bounds on $M_H$. We find that a SM Higgs mass in the range of 160 to 170 GeV will certainly allow for a perturbative and well-behaved SM up to the Planck-mass scale $\Lambda_{Pl}\simeq 10^{19}$ GeV, with no need for new physics to set in below this scale.Comment: 6 pages; to appear in the Proceedings of the ``ECFA/DESY Study on Physics and Detectors for the Linear Collider'', ed. R. Settle

The United States and the LHC

The US government has contributed more than a half billion dollars to the construction of the LHC particle collider and two related experiments in Europe

Large uncertainties in the cross section of elastic WL+WL− W_L^+ W_L^- scattering

The amplitudes for $2\rightarrow 2$ scattering processes involving longitudinally polarized gauge bosons $( W_L^\pm, Z_L )$ and the Higgs boson are analyzed up to two loops. Assuming $M_H >> M_W$, the trilinear Higgs coupling, $\lambda v$, is dominant for energies of $\sqrt{s}$ < 1.5 -- 2 $M_H$. For larger values of $\sqrt{s}$, the quartic coupling, $\lambda$, becomes dominant, allowing for a simpler calculation of higher-order corrections. The high-energy amplitudes display a large logarithmic dependence on $\sqrt{s}$ which can be resummed using renormalization group techniques. The resummation of leading-log terms is sufficient for Higgs masses of less than 350 GeV. For 350 < $M_H$ < 450 GeV, a next-to-leading-log resummation is necessary. For even larger values of $M_H$, the perturbative approach fails completely since two-loop terms become in magnitude larger than one-loop terms. Choosing the $\overline{{\rm MS}}$ renormalization scheme instead of the OMS scheme, the coefficients of the perturbative series increase in magnitude, making the breakdown of perturbation theory even more apparent. In conclusion, the Standard Model cross sections presented here have very large uncertainties if $M_H\gtrsim 450$ GeV and $\sqrt{s} \gtrsim 2 M_H$, reducing the sensitivity to contributions from new physics significantly.Comment: 30 pages, Revtex using epsf, uuencoded, packed Postscript figures. The analysis has been updated to include the 3-loop running coupling. Four figures updated, one figure added to show the maximal energy allowed as a function of the Higgs mass. Final version as to appear in Phys. Rev.

Signal to background

Breathable foam for fire prevention; swords to plowshares; naming LHC magnets; more than 4000 LHC-related papers in spires database; Fermilab’s remote operations center; LHC summer schools at Fermilab and SLAC