The standard model and beyond

The standard model and beyond ÄÚÈݼò½é

¡¡¡¡Much has £¨or has not£© happened in the seven years or so since the publication of the first edition of this book. Most notably£¬ a new spin-0 particle with mass~125 GeV was discovered at the LHC by the ATLAS and CMS collaborations£¬ which is either the elementary Higgs boson or something that closely resembles it. The Higgs discovery completes the ¡Ý40 year saga of verifying the standard model (SM£©. Moreover£¬ its mass is almost maximally interesting£º it is near the top of the range predicted by the most popular SM extension£¬minimal supersymmetry£¬ and near the minimum value consistent with the unextended SM (and then only if the vacuum is metastable£©£¡¡¡¡¡However£¬ the notorious problems of the SM are still unresolved. Perhaps the most press-ing is the apparently fine-tuned hierarchy between the weak interaction and gravity scales.Extensive searches at the LHC and elsewhere have so far not yielded any compelling evidence for new TeV-scale physics such as supersymmetry£¬ extra space dimensions£¬ or strong cou-pling that had been proposed to explain or at least stabilize the hierarchy. Equally puzzling is the nature of the dark energy and its incredibly tiny magnitude compared to most theo-retical expectations. Similarly£¬ numerous experimental attempts to identify the mysterious dark matter inferred from its gravitational effects have not as yet had any positive results and have excluded much of the parameter space for supersymmetric dark matter. And de-spite the great experimental success of the SM£¬ it is a very complicated theory£¬ involving severalinteractions with different properties£¬ and two apparently superfl.uous heavier copies of the fundamental particles that constitute ordinary matter under ordinary conditions. For these and other reasons£¬ many theorists have started exploring less canonical possibilities£¬such as a dark matter sector that is at most very weakly coupled to ordinary particles£¬or£¬ more radically£¬ that the Universe is part of a vast multiverse of regions (presumably associated with a superstring landscape of vacua with different laws of physics.