scholarly journals Complex-Mass Definition and the Structure of Unstable Particle’s Propagator

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Vladimir Kuksa
Keyword(s):  
Spectral Function ◽  
Unstable Particle ◽  
Unstable Particles ◽  
Spinor Fields ◽  
Complex Mass ◽  
Special Case ◽  
Mass Definition

The propagators of unstable particles are considered in framework of the convolution representation. Spectral function is found for a special case when the propagator of scalar unstable particle has Breit-Wigner form. The expressions for the dressed propagators of unstable vector and spinor fields are derived in an analytical way for this case. We obtain the propagators in modified Breit-Wigner forms which correspond to the complex-mass definition.

scholarly journals Moving Unstable Particles and Special Relativity

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Eugene V. Stefanovich
Keyword(s):  
Special Relativity ◽  
Reference Frame ◽  
Unstable Particle ◽  
Internal Variables ◽  
Dirac Theory ◽  
Decay Probability ◽  
Unstable Particles ◽  
Interacting Systems

In Poincaré-Wigner-Dirac theory of relativistic interactions, boosts are dynamical. This means that, just like time translations, boost transformations have a nontrivial effect on internal variables of interacting systems. In this respect, boosts are different from space translations and rotations, whose actions are always universal, trivial, and interaction-independent. Applying this theory to unstable particles viewed from a moving reference frame, we prove that the decay probability cannot be invariant with respect to boosts. Different moving observers may see different internal compositions of the same unstable particle. Unfortunately, this effect is too small to be noticeable in modern experiments.

scholarly journals FACTORIZED FORMULA FOR THE CROSS-SECTION OF TWO-PARTICLE SCATTERING

2008 ◽  
Vol 23 (27n28) ◽  
pp. 4509-4516 ◽  
Author(s):  
V. I. KUKSA
Keyword(s):  
Cross Section ◽  
Intermediate State ◽  
Factorization Method ◽  
Phenomenological Analysis ◽  
Unstable Particle ◽  
Specific Structure ◽  
Particle Scattering ◽  
Unstable Particles ◽  
The Cross ◽  
Exact Factorization

We applied the factorization method to the processes of two-particle scattering with an unstable particle in the intermediate state. It was shown, that in the framework of this method, the cross-section can be represented in the universal factorized form for an arbitrary set of particles. An exact factorization is caused by a specific structure of unstable particles propagators. Phenomenological analysis of the factorization effect is performed.

scholarly journals OpenLoops 2

2019 ◽  
Vol 79 (10) ◽  
Author(s):  
Federico Buccioni ◽  
Jean-Nicolas Lang ◽  
Jonas M. Lindert ◽  
Philipp Maierhöfer ◽  
Stefano Pozzorini ◽  
...  
Keyword(s):  
Scattering Amplitudes ◽  
Open Loop ◽  
The Other ◽  
Automated System ◽  
Special Treatment ◽  
Reduction Algorithm ◽  
Original Algorithm ◽  
Unstable Particles ◽  
Complex Mass ◽  
Gram Determinant

Abstract We present the new version of OpenLoops, an automated generator of tree and one-loop scattering amplitudes based on the open-loop recursion. One main novelty of OpenLoops 2 is the extension of the original algorithm from NLO QCD to the full Standard Model, including electroweak (EW) corrections from gauge, Higgs and Yukawa interactions. In this context, among several new features, we discuss the systematic bookkeeping of QCD–EW interferences, a flexible implementation of the complex-mass scheme for processes with on-shell and off-shell unstable particles, a special treatment of on-shell and off-shell external photons, and efficient scale variations. The other main novelty is the implementation of the recently proposed on-the-fly reduction algorithm, which supersedes the usage of external reduction libraries for the calculation of tree–loop interferences. This new algorithm is equipped with an automated system that avoids Gram-determinant instabilities through analytic methods in combination with a new hybrid-precision approach based on a highly targeted usage of quadruple precision with minimal CPU overhead. The resulting significant speed and stability improvements are especially relevant for challenging NLO multi-leg calculations and for NNLO applications.

scholarly journals Can vanishing mass-on-shell interactions generate a dip at colliders?

2015 ◽  
Vol 30 (20) ◽  
pp. 1550120 ◽  
Author(s):  
Yang Bai ◽  
Wai-Yee Keung
Keyword(s):  
Gauge Boson ◽  
New Physics ◽  
Unstable Particle ◽  
Particle Interactions ◽  
Gauge Bosons ◽  
Complex Mass ◽  
Vector Bosons ◽  
Effective Operators

We categorize new physics signatures that manifest themselves as a “dip” structure at colliders. One potential way to realize a dip is to require interactions to be zero when all particles are mass on-shell, but not if one or more are mass off-shell. For three particle interactions, we have found three interesting cases: one massive gauge boson with two identical scalars; one massless gauge boson with two different scalars; one massive gauge boson with two identical massless gauge bosons. For each case, we identify the relevant effective operators to explore its dip signature at the LHC. Unfortunately, the unstable particle with a vanishing mass-on-shell interaction has a complex mass which is coincident with the complex pole in its propagator. As a result, a contact-like amplitude without a dip is produced. Some interesting collider signatures for “fermion-phobic” vector bosons are also discussed.

scholarly journals QFT Derivation of the Decay Law of an Unstable Particle with Nonzero Momentum

2018 ◽  
Vol 2018 ◽  
pp. 1-7 ◽  
Author(s):  
Francesco Giacosa
Keyword(s):  
Fourier Transform ◽  
Probability Distribution ◽  
Spectral Function ◽  
Rest Frame ◽  
Unstable Particle ◽  
Future Research ◽  
Quantum Field ◽  
Theoretical Derivation ◽  
Decay Products ◽  
Time Dilatation

We present a quantum field theoretical derivation of the nondecay probability of an unstable particle with nonzero three-momentum p. To this end, we use the (fully resummed) propagator of the unstable particle, denoted as S, to obtain the energy probability distribution, called dSp(E), as the imaginary part of the propagator. The nondecay probability amplitude of the particle S with momentum p turns out to be, as usual, its Fourier transform: aSp(t)=∫mth2+p2∞dEdSp(E)e-iEt (mth is the lowest energy threshold in the rest frame of S and corresponds to the sum of masses of the decay products). Upon a variable transformation, one can rewrite it as aSp(t)=∫mth∞dmdS0(m)e-imth2+p2t [here, dS0(m)≡dS(m) is the usual spectral function (or mass distribution) in the rest frame]. Hence, the latter expression, previously obtained by different approaches, is here confirmed in an independent and, most importantly, covariant QFT-based approach. Its consequences are not yet fully explored but appear to be quite surprising (such as the fact that the usual time-dilatation formula does not apply); thus its firm understanding and investigation can be a fruitful subject of future research.

scholarly journals A category mistake in observational claims regarding ultrashort-lived unstable particles

2018 ◽  
Vol 33 (38) ◽  
pp. 1850227
Author(s):  
Marcoen J. T. F. Cabbolet
Keyword(s):  
Higgs Boson ◽  
Standard Model ◽  
Particle Physics ◽  
Empirical Support ◽  
Unstable Particle ◽  
Category Mistake ◽  
Unstable Particles ◽  
The Standard Model ◽  
Physics Literature ◽  
General Note

The physics literature contains many claims that ultrashort-lived unstable particles, such as a Higgs boson, have been observed. These claims are a matter of applying the [Formula: see text]-convention in particle physics. This paper, however, shows that by applying this [Formula: see text]-convention a category mistake is made, by which a pure reasoning is passed off as an observation. Not only are these two fundamentally different primitive notions at the very basis of science, but the pure reasoning in question is also weaker than an observation: what we have in each case is that the existence of the ultrashort-lived unstable particle is inferred to the best explanation, but that does absolutely not merit the stronger claim that the particle in question has been “observed”. Consequently, the observational claims in question will thus have to be dismissed as overstatements. On a general note, this demonstrates that the empirical support for the Standard Model of particle physics is significantly less than hitherto thought.

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