Top Pole Mass Research Articles

The Asymptotically Safe Standard Model: From quantum gravity to dynamical chiral symmetry breaking

We present a comprehensive non-perturbative study of the phase structure of the asymptotically safe Standard Model. The physics scales included range from the asymptotically safe trans-Planckian regime in the ultraviolet, the intermediate high-energy regime with electroweak symmetry breaking to strongly correlated QCD in the infrared. All flows are computed with a self-consistent functional renormalisation group approach, using a vertex expansion in the fluctuation fields. In particular, this approach takes care of all physical threshold effects and the respective decoupling of ultraviolet degrees of freedom. Standard Model and gravity couplings and masses are fixed by their experimental low energy values. Importantly, we accommodate for the difference between the top pole mass and its Euclidean analogue. Both, the correct mass determination and the threshold effects have a significant impact on the qualitative properties, and in particular on the stability properties of the specific ultraviolet-infrared trajectory with experimental Standard Model physics in the infrared. We show that in the present rather advanced approximation the matter part of the asymptotically safe Standard Model has the same number of relevant parameters as the Standard Model, and is asymptotically free. This result is based on the novel UV fixed point found in the present work: the fixed point Higgs potential is flat but has two relevant directions. These results and their analysis are accompanied by a thorough discussion of the systematic error of the present truncation, also important for systematic improvements.

Hyperasymptotic approximation to the top, bottom, and charm pole mass

We construct hyperasymptotic expansions for the heavy quark pole mass regulated using the principal value (PV) prescription. We apply such hyperasymptotic expansions to the $B/D$ meson masses, and $\bar \Lambda $ computed in the lattice. The issue of the uncertainty of the (top) pole mass is critically reexamined. The present theoretical uncertainty in the relation between ${\bar m}_t$, the $\bar{\rm MS}$ top mass, and $m_{t, \rm PV}$, the top pole mass regulated using the PV prescription, is numerically assessed to be $\delta m_{t,\rm PV}= 28\;{\rm MeV}$ for ${\bar m}_t =163$ GeV.

Top mass from asymptotic safety

We discover that asymptotically safe quantum gravity could predict the top-quark mass. For a broad range of microscopic gravitational couplings, quantum gravity could provide an ultraviolet completion for the Standard Model by triggering asymptotic freedom in the gauge couplings and bottom Yukawa and asymptotic safety in the top-Yukawa and Higgs-quartic coupling. We find that in a part of this range, a difference of the top and bottom mass of approximately 170GeV is generated and the Higgs mass is determined in terms of the top mass. Assuming no new physics below the Planck scale, we construct explicit Renormalization Group trajectories for Standard Model and gravitational couplings which link the transplanckian regime to the electroweak scale and yield a top pole mass of Mt,pole≈171GeV.

Gravitational effects on vanishing Higgs potential at the Planck scale

We investigate gravitational effects on the so-called multiple point criticality principle (MPCP) at the Planck scale. The MPCP requires two degenerate vacua, whose necessary conditions are expressed by vanishing Higgs quartic coupling $\lambda(M_{\rm Pl})=0$ and vanishing its $\beta$ function $\beta_\lambda(M_{\rm Pl})=0$. We discuss a case that a specific form of gravitational corrections are assumed to contribute to $\beta$ functions of coupling constants although it is accepted that gravitational corrections do not alter the running of the standard model (SM) couplings. To satisfy the above two boundary conditions at the Planck scale, we find that the top pole mass and the Higgs mass should be $170.8\,{\rm GeV} \lesssim M_t\lesssim 171.7\,{\rm GeV}$ and $M_h=125.7\pm0.4\,{\rm GeV}$, respectively, as well as include suitable magnitude of gravitational effects (a coefficient of gravitational contribution as $|a_\lambda| > 2$). In this case, however, since the Higgs quartic coupling $\lambda$ becomes negative below the Planck scale, two vacua are not degenerate. We find that $M_h \gtrsim 131.5\,{\rm GeV}$ with $M_t \gtrsim 174\,{\rm GeV}$ is required by the realization of the MPCP. Therefore, the MPCP at the Planck scale cannot be realized in the SM and also the SM with gravity since $M_h \gtrsim 131.5\,{\rm GeV}$ is experimentally ruled out.

Measurements of top quark properties with the ATLAS detector

A selection of recent top quark measurements performed with the ATLAS detector is presented here, with data taken in 2011 and 2012 at centre-of-mass energies of 7 TeV and 8 TeV, respectively. The analyses cover the determination of the top pole mass by a cross-section measurement, the top/anti-top quark mass difference, the spin correlation and the charge asymmetry. No hints for physics beyond the Standard Model have been found but a great reduction of uncertainties compared to former results was achieved.

Planck scale boundary conditions in the standard model with singlet scalar dark matter

We investigate Planck scale boundary conditions on the Higgs sector of the standard model with a gauge singlet scalar dark matter. We will find that vanishing self-coupling and Veltman condition at the Planck scale are realized with the 126 GeV Higgs mass and top pole mass, 172 GeV $\lesssim M_t\lesssim$ 173.5 GeV, where a correct abundance of scalar dark matter is obtained with mass of 300 GeV $\lesssim m_S \lesssim$ 1 TeV. It means that the Higgs potential is flat at the Planck scale, and this situation can not be realized in the standard model with the top pole mass.

Another calculation of the Higgs mass and the top mass from the principles of H. B. Nielsen: $m_H\cong 163$ GeV for $M_t\cong 190$ GeV

We calculate the Higgs mass and the top mass starting from the principle that there are two, essentially degenerate minima in the Higgs effective potential; the second is at about the Planck energy scale M P = 1.2 × 1019 GeV. Thus the parameter of the quartic self-coupling λ h vanishes, as does β λH at M P. The new element is the addition of a quantum interaction term which couples the square of the Higgs field to the square of a pseudoscalar field, in the domain of the energy scale between about 1014 GeV and M P. We modify β λH at one loop. The pseudoscalar field which is introduced may be the field which is responsible for a spontaneous breakdown of discrete symmetry — for CP noninvariance at an energy scale of (1015–1016) GeV. The result is then a closer value for m H ≅ 163 GeV for the top pole-mass M t ≅ 190 GeV; both values are now close to the electroweak scale parameter \(\langle {\phi _H}\rangle /\sqrt 2 = 175{\text{ GeV}}\). In terms of dimensionless running coupling parameters, which determine the masses near to the electroweak scale, we get \(\sqrt {{\lambda _H}} \cong 0.06\) and \(gt/\sqrt 2 \cong 0.72\), values that are close to each other and close to unity.