A
bstract
We discuss renormalization group equations (RGE) for the parameters of the Higgs sector in general Two-Higgs-Doublet Model (2HDM). We present the three-loop results but consider only ...contributions due to self-couplings of the Higgs doublets. We study the structure of RGE and express beta-functions in terms of reparametrization invariants with respect to higgs-basis rotations. The Cayley-Hamilton theorem is utilized to reduce both the number of independent tensor structures in matrix RGE and the number of invariants to a minimal set. As a by-product of our calculation we discovered that two-loop RGE of the scalar sector in general QFT with multiple higgses were not properly implemented in a number of public packages. The latter give rise to a wrong result when mixing in the scalar sector is allowed.
We perform a manifestly gauge-independent analysis of the vacuum stability in the standard model including two-loop matching, three-loop renormalization group evolution, and pure QCD corrections ...through four loops. All these ingredients are exact, except that light-fermion masses are neglected. We in turn apply the criterion of nullifying the Higgs self-coupling and its beta function in the modified minimal-subtraction scheme and a recently proposed consistent method for determining the true minimum of the effective Higgs potential that also avoids gauge dependence. Exploiting our knowledge of the Higgs-boson mass, we derive an upper bound on the pole mass of the top quark by requiring that the standard model be stable all the way up to the Planck mass scale and conservatively estimate the theoretical uncertainty. This bound is compatible with the Monte Carlo mass quoted by the Particle Data Group at the 1.3σ level.
In this Letter we consider renormalization of a class of scalar operators with fixed hypercharge Q within the Standard Model. We carry out explicit computation of the corresponding anomalous ...dimensions up to the three-loop order. In spite of the fact that our result is gauge-dependent, in the Landau gauge and in the limit of vanishing weak isospin coupling the expression can be matched to recent gauge-independent computation based on the large-charge method. Our result serves an important and non-trivial cross-check of new developments in large-charge expansion and applications of the latter to realistic gauge theories. We not only confirm the leading and subleading terms in perturbative Q expansion up to three loops, but also provide the expressions for sub-subleading coefficients that at the moment are not captured by the large-charge approach.
We investigate the possibility to constrain the intrinsic charm probability
w
c
c
¯
=
P
c
c
¯
/
p
using first ATLAS data on the associated production of prompt photons and charm-quark jets in
pp
...collisions at
s
=
8
TeV. The upper limit
w
c
c
¯
<
1.93
% is obtained at the 68 % confidence level. This constraint is primarily determined from the theoretical scale and systematical experimental uncertainties. Suggestions for reducing these uncertainties are discussed. The implications of intrinsic heavy quarks in the proton for future studies at the LHC are also discussed.
The effective renormalizable theory describing electromagnetic and strong interactions of quarks of five light flavors (nf=5QCD×QED) is considered as a low-energy limit of the full Standard Model. ...Two-loop relation between the running strong coupling constants αs defined in either theories is found by simultaneous decoupling of electroweak gauge and Higgs bosons in addition to the top-quark. The relation potentially allows one to confront “low-energy” determination of αs with a high-energy one with increased accuracy. Numerical impact of new O(αsα) terms is studied at the MZ scale. It is shown that the corresponding contribution, although being suppressed with respect to O(αs2) terms, is an order of magnitude larger than the three-loop QCD corrections O(αs3) usually taken into account in four-loop renormalization group evolution of αs. The dependence on the matching scale is also analyzed numerically.
The approach proposed earlier for describing the scattering of weakly interacting nonrelativistic massive neutral particles off nuclei is used as the basis to derive explicit expressions for the ...event counting rate expected in experiments aimed at directly detecting dark matter (DM) particles. These expressions make it possible to estimate the rates in question with allowance for both elastic (coherent) and inelastic (incoherent) channels of DM particle interaction with a target nucleus. Within this approach, the effect of a nonzero excitation energy of the nucleus involved is taken into account for the first time in calculating the contribution of inelastic processes. A correlation between the excitation energy and admissible values of the kinetic recoil energy of the excited nucleus constrains substantially the possibility of detection of the inelastic channel with some nuclei. In addition to the standard model of the DM distribution in the Milky Way Galaxy, the effect of some other models that allow significantly higher velocities of DM particles is considered. A smooth transition from the dominance of the elastic channel of the DM particle–nucleus interaction to the dominance of its inelastic channel occurs as the nuclear recoil energy
grows. If the DM detector used is tuned to detecting elastic-scattering events exclusively, then it cannot detect anything in the case where the nuclear recoil energy turns out to be below the the detection threshold. As
grows, such a detector loses the ability to see anything, since elastic processes quickly become nonexistent. Radiation associated with the deexcitation of the nucleus becomes the only possible signature of the interaction that occurred. In the case of a spin-independent interaction, the inelastic contribution becomes dominant rather quickly as
grows, while the differential event counting rate decreases insignificantly. If a DM particle interacts with nucleons via a spin-dependent coupling exclusively, detectors traditionally set up to detect an elastic spin-dependent DM signal will be unable to to see anything since the signal entirely goes through the inelastic channel. It looks like the sought interactions of DM particles may have a sizable intensity, but the instrument is unable to detect them.
Therefore, experiments aimed at directly detecting DM particles should be planned in such a way that it would be possible to detect simultaneously two signals—that of the recoil energy of the nucleus involved and that of gamma rays having a specific energy and carrying away its excitation. A experiment in this implementation will furnish complete information about the DM interaction that occurred.
We present the results for three-loop beta-functions for Yukawa couplings of heavy Standard Model fermions calculated within the unbroken phase of the model. The calculation is carried out with the ...help of the MINCER program in a general linear gauge, and the final result is independent of the gauge-fixing parameters. In order to calculate three-point functions, we made use of infrared rearrangement (IRR) trick. Due to the chiral structure of the SM a careful treatment of loops with fermions is required to perform the calculation. It turns out that gauge anomaly cancellation in the SM allows us to obtain the result by means of the semi-naive treatment of γ5.
We consider an observable very sensitive to the nonzero intrinsic charm (IC) contribution to the proton density. It is the ratio between the differential cross sections of the photon or Z-boson and ...c-jet production in the pp collision, γ(Z)+c, and the γ(Z) and the b-jet production. It is shown that this ratio can be approximately flat or increasing at large γ(Z) transverse momenta pT, and their pseudorapidities 1.5<η<2.4 if the IC contribution is taken into account. On the contrary, in the absence of the IC, this ratio decreases as pT grows. We also present the ratios of the cross sections integrated over pT as a function of the IC probability w. It is shown that these ratios are mostly independent on the theoretical uncertainties, and such predictions could therefore be much more promising for the search for the intrinsic charm signal at the LHC compared to the predictions for pT spectra, which significantly depend on these uncertainties.
In this letter we present our results for the four-loop beta-function of the strong coupling in the Standard Model of fundamental interactions. The expression is obtained from gluon self-energy ...diagrams in the background field gauge without application of special infra-red rearrangement tricks. We take top-Yukawa and self-Higgs interactions into account, but neglect electroweak gauge couplings. Ambiguities due to γ5 treatment are discussed and a particular “reading” prescription for odd Dirac traces is advocated.
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