arXiv subjects
Publications and source records attributed to B. Holdom.
For a heavy Higgs boson above the $t\bar t$ threshold we consider three decay modes that could compete with decay to $t\bar t$, even in the alignment limit of a 2-Higgs doublet model. The decays $H\to AZ$, $ Z'Z'$ and $τ'τ'$ show that heavy Higgs decays can be an effective probe of new physics both within and beyond this model.
New heavy leptons with standard model gauge couplings have well determined cross sections for pair production. A standard pattern of mass mixing implies that the most likely decays are $τ^\prime\to W ν'$ and $ ν'\to W τ$. Interestingly there have been no direct searches for heavy leptons with these decays at the LHC. However comparison with several multi-lepton searches allow us to set new limits on the heavy lepton masses. Three observed excesses in the signal regions prevent us from setting stronger limits.
We suggest that the Higgs is a light composite state that does not emerge from TeV scale strong dynamics for any generic reason, such as when it is pseudo-Goldstone boson. Instead, a state that is Higgs-like and fairly decoupled from heavier states may simply be a reflection of very particular strong dynamics, with properties quite distinct from more familiar large-$N_c$ type gauge dynamics. We elaborate on this picture in the context of a strongly interacting fourth family and an effective 4-Higgs-doublet model. The origin of a decoupling limit and the corrections to it are discussed.
From the operator product expansion the gluon condensate controls a certain power law correction to the ultraviolet behavior of the gauge theory. This is reflected by the asymptotic behavior of the effective gluon mass function as determined by its Schwinger-Dyson equation. We show that the current state of the art determination of the gluon mass function by Binosi, Ibanez and Papavassiliou points to a vanishing gluon condensate. If this is correct then the vacuum energy also vanishes in massless QCD. This result can be interpreted as a statement about a softness in the ultraviolet behavior and the consistency of this behavior with a mass gap.
A theory input is needed for the estimation of the largest background for the $H\rightarrow WW$ search at the LHC. This is the shape of the $m_{\ell\ell}$ spectrum from continuum $WW$ production. We find this to depend on how NLO matrix elements are merged with parton showers, and we compare the results from a number of different implementations. The results suggest that both the size of the background estimate and its uncertainty may have been underestimated. This conclusion is reinforced by a "Note Added", which comments on the LHC results released on November 14 2012.
In this short note we consider a permitted region in the space of couplings of the 126 GeV boson that extends far away from the standard model Higgs couplings. This region is of interest for more natural models of electroweak symmetry breaking. Stronger evidence of vector boson fusion and/or associated production is needed to eliminate this possibility.
A pseudoscalar associated with dynamical symmetry breaking can mix with a heavier scalar when CP is violated. We study how such a mixed state that is mostly pseudoscalar can resemble the observed 125 GeV particle. The production rate from $gg$ is enhanced by the new heavy quarks and this compensates for the reduced $WW$, $ZZ$ and $γγ$ branching ratios. The particle can appear to be a scalar from angular distributions in $ZZ$ decay while its pseudoscalar couplings should become evident in other processes.
A new particle of mass around 125 GeV is known to have loop induced couplings to $gg$ and $γγ$. More specific to the Higgs interpretation are tree level couplings to $W$ and $Z$. A small but clean signal of the Higgs coupling to $W$ arises from associated production of a Higgs, with $H\rightarrowγγ$. We consider this signal in light of a large NLO enhancement of the irreducible background.
Condensates of colored fermions driving electroweak symmetry breaking could give rise to a light pseudoscalar that would show up in the Higgs search at the LHC. The branching ratios of its decay will distinguish it from the Higgs and illuminate its origin. In particular the colored fermions may be the techniquarks of a one family technicolor theory or the quarks of a strongly interacting fourth family. The former has more difficulties in this context.
The new quarks of a fourth family are being pushed into the strongly interacting regime due to the lower limits on their masses. The theoretical basis and experimental implications of such quarks are compared with exotic quarks.
We consider the production and detection of a sequential, down type quark via the mode $p p \to b' {\bar b}' \to W^+ W^- t {\bar t} \to \ell ν_{\ell} 8 j$ at the LHC, with the collision energy $\sqrt{s}=10$ TeV and the total integrated luminosity around 1 fb$^{-1}$. We assume $m_{b'}=m_{t'}=600$ GeV. A full reconstruction is employed and the signal and background discrimination is studied within a neural network approach. Our results show that this mode can make a useful contribution to the $b'$ search.
The infrared divergence of the self-energy of a color charge is due to an enhancement of the long wavelength modes of the color Coulomb potential field. There are also long wavelength contributions to the QCD vacuum energy that are similarly enhanced. Vacuum modes of Hubble scale wavelengths may be affected in a cosmological setting and this can lead to a residual positive energy density of the form $H^dΛ_{\rm QCD}^{4-d}$. Lattice studies constrain $d$. If the dark energy takes this form then the universe is driven towards de Sitter expansion, and we briefly study this cosmology when $d$ is just slightly above unity.
The existence of Gribov copies is a central feature of the field configuration space of confining gauge theories. In particular a transition between two Gribov copies with relative winding number implies a space-time configuration with topological charge. We explicitly demonstrate the proliferation of Gribov copies with relative winding number, where our focus is on localized (finite norm) configurations in Coulomb gauge. We then discuss the likelihood that some pairs of such copies are connected by Minkowski space solutions. We also comment on the relative importance of instantons and the connection to confinement.
$β$-functions for abelian and non-abelian gauge theories are studied in the regime where the large $N$ flavor expansion is applicable. The first nontrivial order in the 1/$N$ expansion is known for any value of $Nα$, and there are also various indications as to the nature of higher order effects. The singularity structure as a function of $Nα$ has implications for the existence of nontrivial fixed points.
A heavy fourth family is an example of new physics which is well defined and familiar in some respects, but which nevertheless has radical implications. In particular it eliminates a light Higgs description of electroweak symmetry breaking. We discuss an early signal for heavy quarks at the LHC in the form of an excess of "$W$-jets", and as well show how $W$-jets may be useful in the reconstruction of the heavy quark masses. We argue that fourth family quarks can be distinguished from vector-like quarks of a similar mass at roughly the same time that a same sign lepton signal becomes visible. Given the large mass of the fourth neutrino we describe how a picture for neutrino mass emerges in the absence of right-handed neutrinos, and how it suggests the existence of a remnant flavor gauge symmetry. Based on talk given at "Second Workshop on Beyond 3 Generation Standard Model -- New Fermions at the Crossroads of Tevatron and LHC", January 2010, Taipei Taiwan.
This summary of the Workshop "Beyond the 3-generation SM in the LHC era" presents a brief discussion of the following four statements about the fourth generation: 1) It is not excluded by EW precision data; 2) It addresses some of the currently open questions; 3) It can accommodate emerging possible hints of new physics; 4) LHC has the potential to discover or fully exclude it.
Negative correlations in the distribution of prime numbers are found to display a scale invariance. This occurs in conjunction with a nonstationary behavior. We compare the prime number series to a type of fractional Brownian motion which incorporates both the scale invariance and the nonstationary behavior. Interesting discrepancies remain. The scale invariance also appears to imply the Riemann hypothesis and we study the use of the former as a test of the latter.
We consider soft nonlocal deformations of massless theories that introduce a mass gap. By use of a renormalization scheme that preserves the ultraviolet softness of the deformation, renormalized quantities of low mass dimension, such as normal mass terms, vanish via finite counterterms. The same applies to the renormalized cosmological constant. We connect this discussion to gauge theories, since they are also subject to a soft nonlocal deformation due to the effects of Gribov copies. These effects are softer than usually portrayed.