scholarly journals Long-Lived Heavy Quarks: A Review

2013 ◽  
Vol 2013 ◽  
pp. 1-17 ◽  
Author(s):  
Mathieu Buchkremer ◽  
Alexander Schmidt
Keyword(s):  
Standard Model ◽  
Bound States ◽  
Experimental Situation ◽  
Heavy Quarks ◽  
The Past ◽  
Analysis Methods ◽  
Detector Acceptance ◽  
The Standard Model

We review the theoretical and experimental situation for long-lived heavy quarks, or bound states thereof, arising in simple extensions of the Standard Model. If these particles propagate large distances before their decay, they give rise to specific signatures requiring dedicated analysis methods. In particular, vector-like quarks with negligible couplings to the three known families could have eluded the past experimental searches. While most analyses assume prompt decays at the production vertex, novel heavy quarks might lead to signatures involving displaced vertices, new hadronic bound states, or decays happening outside of the detector acceptance. We perform reinterpretations of existing searches for short- and long-lived particles, and give suggestions on how to extend their reach to long-lived heavy quarks.

scholarly journals Testing the mechanism of lepton compositeness

2021 ◽  
Vol 10 (3) ◽  
Author(s):  
Vincenzo Afferrante ◽  
Axel Maas ◽  
René Sondenheimer ◽  
Pascal Törek
Keyword(s):  
Gauge Theory ◽  
Standard Model ◽  
Gauge Invariance ◽  
Bound States ◽  
Lattice Gauge Theory ◽  
Higgs Field ◽  
Left Handed ◽  
Lattice Gauge ◽  
The Standard Model ◽  
Weyl Fermions

Strict gauge invariance requires that physical left-handed leptons are actually bound states of the elementary left-handed lepton doublet and the Higgs field within the standard model. That they nonetheless behave almost like pure elementary particles is explained by the Fr"ohlich-Morchio-Strocchi mechanism. Using lattice gauge theory, we test and confirm this mechanism for fermions. Though, due to the current inaccessibility of non-Abelian gauged Weyl fermions on the lattice, a model which contains vectorial leptons but which obeys all other relevant symmetries has been simulated.

Lattice QCD Results and Prospects

2003 ◽  
Vol 18 (supp01) ◽  
pp. 1-26
Author(s):  
Richard Kenway
Keyword(s):  
Standard Model ◽  
Lattice Qcd ◽  
Strong Interaction ◽  
Bound States ◽  
Leading Edge ◽  
Beyond The Standard Model ◽  
Quark Masses ◽  
The Standard Model ◽  
Quark Flavour ◽  
Computationally Intensive

In the Standard Model, quarks and gluons are permanently confined by the strong interaction into hadronic bound states. The values of the quark masses and the strengths of the decays of one quark flavour into another cannot be measured directly, but must be deduced from experiments on hadrons. This requires calculations of the strong-interaction effects within the bound states, which are only possible using numerical simulations of lattice QCD. These are computationally intensive and, for the past twenty years, have exploited leading-edge computing technology. In conjunction with experimental data from B Factories, over the next few years, lattice QCD may provide clues to physics beyond the Standard Model. These lectures provide a non-technical introduction to lattice QCD, some of the recent results, QCD computers, and the future prospects.

scholarly journals QCD THEORY

2005 ◽  
Vol 20 (22) ◽  
pp. 5234-5243
Author(s):  
W. J. STIRLING
Keyword(s):  
Standard Model ◽  
Quantum Chromodynamics ◽  
High Energy ◽  
New Physics ◽  
Status Report ◽  
The Past ◽  
The Standard Model

Quantum Chromodynamics is an established part of the Standard Model and an essential part of the toolkit for searching for new physics at high-energy colliders. I present a status report on the theory of QCD and review some of the important developments in the past year.

scholarly journals Quantum stabilization of cosmic strings

2015 ◽  
Vol 30 (27) ◽  
pp. 1530022 ◽  
Author(s):  
H. Weigel ◽  
M. Quandt ◽  
N. Graham
Keyword(s):  
Standard Model ◽  
Top Quark ◽  
Cosmic String ◽  
Bound States ◽  
Degrees Of Freedom ◽  
Energy Levels ◽  
Binding Energies ◽  
Fermion Mass ◽  
The Standard Model ◽  
A Charge

In the standard model, stabilization of a classically unstable cosmic string may occur through the quantum fluctuations of a heavy fermion doublet. We review numerical results from a semiclassical expansion in a reduced version of the standard model. In this expansion, the leading quantum corrections emerge at one loop level for many internal degrees of freedom. The resulting vacuum polarization energy and the binding energies of occupied fermion energy levels are of the same order, and must therefore be treated on equal footing. Populating these bound states lowers the total energy compared to the same number of free fermions and assigns a charge to the string. Charged strings are already stabilized for a fermion mass only somewhat larger than the top quark mass. Though obtained in a reduced version, these results suggest that neither extraordinarily large fermion masses nor unrealistic couplings are required to bind a cosmic string in the standard model. Furthermore, we also review results for a quantum stabilization mechanism that prevents closed Nielsen–Olesen-type strings from collapsing.

scholarly journals A TORSIONAL MODEL OF LEPTONS

2012 ◽  
Vol 27 (34) ◽  
pp. 1250199 ◽  
Author(s):  
LUCA FABBRI
Keyword(s):  
Standard Model ◽  
Bound States ◽  
Weak Interactions ◽  
Specific Mass ◽  
The Standard Model

Quite recently it was shown that torsion induces interactions among leptons that are identical to the weak interactions of leptons of the Weinberg Standard Model, if it is in terms of leptonic bound states that the bosonic sector is built; here we obtain the partially conserved axial currents showing that they are the same of the Standard Model, if the composite mediators have specific mass relationships: we show that their masses are indeed the measured ones, if reasonable approximations are taken.

scholarly journals Long-lived heavy neutral leptons at the LHC: four-fermion single-NR operators

2022 ◽  
Vol 2022 (1) ◽  
Author(s):  
Rebeca Beltrán ◽  
Giovanna Cottin ◽  
Juan Carlos Helo ◽  
Martin Hirsch ◽  
Arsenii Titov ◽  
...  
Keyword(s):  
Field Theory ◽  
Standard Model ◽  
Effective Field Theory ◽  
New Physics ◽  
Effective Field ◽  
High Luminosity ◽  
The Past ◽  
The Standard Model ◽  
Model Independent

Abstract Interest in searches for heavy neutral leptons (HNLs) at the LHC has increased considerably in the past few years. In the minimal scenario, HNLs are produced and decay via their mixing with active neutrinos in the Standard Model (SM) spectrum. However, many SM extensions with HNLs have been discussed in the literature, which sometimes change expectations for LHC sensitivities drastically. In the NRSMEFT, one extends the SM effective field theory with operators including SM singlet fermions, which allows to study HNL phenomenology in a “model independent” way. In this paper, we study the sensitivity of ATLAS to HNLs in the NRSMEFT for four-fermion operators with a single HNL. These operators might dominate both production and decay of HNLs, and we find that new physics scales in excess of 20 TeV could be probed at the high-luminosity LHC.

scholarly journals Collider signatures of coannihilating dark matter in light of the B-physics anomalies

2021 ◽  
Vol 2021 (11) ◽  
Author(s):  
Michael J. Baker ◽  
Darius A. Faroughy ◽  
Sokratis Trifinopoulos
Keyword(s):  
Dark Matter ◽  
Standard Model ◽  
Bound States ◽  
B Physics ◽  
Search Strategy ◽  
Dark Matter Candidate ◽  
Final States ◽  
Dark Sector ◽  
Decay Modes ◽  
The Standard Model

Abstract Motivated by UV explanations of the B-physics anomalies, we study a dark sector containing a Majorana dark matter candidate and a coloured coannihilation partner, connected to the Standard Model predominantly via a U1 vector leptoquark. A TeV scale U1 leptoquark, which couples mostly to third generation fermions, is the only successful single-mediator description of the B-physics anomalies. After calculating the dark matter relic surface, we focus on the most promising experimental avenue: LHC searches for the coloured coannihilation partner. We find that the coloured partner hadronizes and forms meson-like bound states leading to resonant signatures at colliders reminiscent of the quarkonia decay modes in the Standard Model. By recasting existing dilepton and monojet searches we exclude coannihilation partner masses less than 280 GeV and 400 GeV, respectively. Since other existing collider searches do not significantly probe the parameter space, we propose a new dedicated search strategy for pair production of the coloured partner decaying into bbττ final states and dark matter particles. This search is expected to probe the model up to dark matter masses around 600 GeV with current luminosity.

scholarly journals BOUND-STATE/ELEMENTARY-PARTICLE DUALITY IN THE HIGGS SECTOR AND THE CASE FOR AN EXCITED "HIGGS" WITHIN THE STANDARD MODEL

2013 ◽  
Vol 28 (28) ◽  
pp. 1350103 ◽  
Author(s):  
AXEL MAAS
Keyword(s):  
Elementary Particle ◽  
Standard Model ◽  
Cross Sections ◽  
Bound States ◽  
Weak Interactions ◽  
Higgs Sector ◽  
Bound State ◽  
Leading Order ◽  
Expectation Value ◽  
The Standard Model

Though being weakly interacting, QED can support bound states. In principle, this can be expected for the weak interactions in the Higgs sector as well. In fact, it has been argued long ago that there should be a duality between bound states and the elementary particles in this sector, at least in leading order in an expansion in the Higgs quantum fluctuations around its expectation value. Whether this remains true beyond the leading order is being investigated using lattice simulations, and support is found. This provides a natural interpretation of peaks in cross-sections as bound states. This would imply that (possibly very broad) resonances of Higgs and W and Z bound states could exist within the Standard Model.

LIMITS FROM LEP 2 ON POSSIBLE ENHANCEMENT OF Re ∊′/∊ DUE TO ANOMALOUS GAUGE BOSON COUPLINGS

2001 ◽  
Vol 16 (supp01b) ◽  
pp. 669-671
Author(s):  
FRANCESCO TERRANOVA
Keyword(s):  
Standard Model ◽  
Low Energy ◽  
Hadron Colliders ◽  
Anomalous Couplings ◽  
The Past ◽  
The Poor ◽  
The Standard Model ◽  
Energy Processes ◽  
The Impact ◽  
Gauge Boson Couplings

It has been shown in the past that the real part of the ∊′/∊ ratio is particularly sensitive to anomalous gauge couplings that modify the Standard Model Lagrangian. Due to the loose bounds on these couplings coming from low energy processes and to the poor sensitivity of hadron colliders to couplings such as [Formula: see text], it has been argued that anomalous couplings could still produce an enhancement of Re ∊′/∊ bringing this observable closer to the experimental value obtained by KTeV, NA31 and NA48. The impact of the new measurements done at LEP2 in these years is discussed and new severe constraints to this hypothesis are determined.

SEARCHES FOR THE STANDARD MODEL HIGGS BOSON AT THE CDF EXPERIMENT

2009 ◽  
Vol 24 (04) ◽  
pp. 617-656
Author(s):  
SONG-MING WANG
Keyword(s):  
Higgs Boson ◽  
Standard Model ◽  
High Energy Physics ◽  
High Energy ◽  
Electroweak Symmetry ◽  
The Past ◽  
The Standard Model ◽  
Using Data ◽  
Near Future ◽  
Energy Physics

The understanding of the dynamics behind the breaking of the electroweak symmetry is one of the most important goals in the field of high energy physics. In the Standard Model (SM) Higgs mechanism plays a key role in the symmetry breaking, one manifestation of which is spin-0 Higgs boson. Thus the search for the Higgs boson is one of the flag-ship analyses at the Tevatron. Over the past few years the CDF experiment has made significant improvements in its sensitivity on the search for the SM Higgs boson. In this paper we summarize CDF's most recent results on the searches for the SM Higgs boson production at the Tevatron using data samples of integrated luminosities up to 3 fb-1. We also present the Tevatron's latest combined results on the SM Higgs boson search, and discuss the possibility that it could be found at the Tevatron in the near future.

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