[Paper Review] Stable quarks of the 4th family?

K. M. Belotsky, Maxim Khlopov+1 more|ArXiv.org|Jun 5, 2008

Dark Matter and Cosmic Phenomena36 references14 citations

TL;DR

This paper proposes that metastable fourth-generation quarks—specifically the up-type quark (U)—could exist due to a new U(1) gauge symmetry (y-charge) that stabilizes them, enabling formation of exotic hadrons like doubly charged baryons and bound states with helium-4. These particles could evade current experimental limits, contribute to dark matter as a warm, nuclear-interacting form, and leave detectable signatures in cosmic rays, neutrino fluxes, and electromagnetic spectra.

ABSTRACT

Existence of metastable quarks of new generation can be embedded into phenomenology of heterotic string together with new long range interaction, which only this new generation possesses. We discuss primordial quark production in the early Universe, their successive cosmological evolution and astrophysical effects, as well as possible production in present or future accelerators. In case of a charge symmetry of 4th generation quarks in Universe, they can be stored in neutral mesons, doubly positively charged baryons, while all the doubly negatively charged "baryons" are combined with He-4 into neutral nucleus-size atom-like states. The existence of all these anomalous stable particles may escape present experimental limits, being close to present and future experimental test. Due to the nuclear binding with He-4 primordial lightest baryons of the 4th generation with charge +1 can also escape the experimental upper limits on anomalous isotopes of hydrogen, being compatible with upper limits on anomalous lithium. While 4th quark hadrons are rare, their presence may be nearly detectable in cosmic rays, muon and neutrino fluxes and cosmic electromagnetic spectra. In case of charge asymmetry, a nontrivial solution for the problem of dark matter (DM) can be provided by excessive (meta)stable anti-up quarks of 4th generation, bound with He-4 in specific nuclear-interacting form of dark matter. Such candidate to DM is surprisingly close to Warm Dark Matter by its role in large scale structure formation. It catalyzes primordial heavy element production in Big Bang Nucleosynthesis and new types of nuclear transformations around us.

Motivation & Objective

• To explore the cosmological and astrophysical viability of metastable fourth-generation quarks stabilized by a new U(1) gauge symmetry (y-charge).
• To analyze the production and relic abundance of U-quark hadrons in the early Universe, particularly under conditions of charge symmetry or asymmetry.
• To assess the detectability of these exotic hadrons in cosmic rays, accelerator experiments, and their potential role in dark matter and Big Bang nucleosynthesis.
• To evaluate constraints from anomalous isotopes (e.g., hydrogen, lithium) and nuclear binding effects with helium-4.
• To propose a novel dark matter candidate based on neutral, y-interacting U-hadron bound states with 4He, offering a warm dark matter-like behavior.

Proposed method

• Adopt a phenomenological model based on heterotic string theory with a new U(1) gauge symmetry (y-charge) conserved only by 4th-generation fermions.
• Model primordial production of U-quark hadrons during Big Bang Nucleosynthesis (BBN), assuming thermal freeze-out and subsequent cosmological evolution.
• Analyze binding of (UUD)++ and (ŪŪŪ)--- baryons with 4He nuclei into neutral, atom-like states, using Coulomb-like y-interaction to stabilize these systems.
• Use cosmological constraints on anomalous isotopes (e.g., 1H, 4He) and BBN to set bounds on U-quark lifetime and abundance.
• Estimate fluxes of U-hadrons in cosmic rays via spallation of high-energy cosmic rays on galactic matter, comparing with AMS02 and PAMELA sensitivity.
• Assess collider signatures: high-pT, low-velocity U-hadrons with charge-flipping effects in detectors, enabling efficient background rejection.

Experimental results

Research questions

• RQ1 Can a new U(1) gauge symmetry (y-charge) stabilize the lightest fourth-generation quark (U-quark), preventing decay and enabling long-lived hadrons?
• RQ2 What are the cosmological and astrophysical signatures of U-hadrons, particularly in cosmic ray fluxes and electromagnetic spectra?
• RQ3 How do nuclear binding effects with 4He nuclei suppress or stabilize exotic hadrons like (ŪŪŪ)--- and (UUD)++ in matter?
• RQ4 Can U-hadrons with electric charge +1 or -2 evade experimental limits on anomalous isotopes of hydrogen and helium?
• RQ5 Can a cosmological asymmetry in 4th-generation quarks lead to a viable, nuclear-interacting dark matter candidate via y-interaction-bound states with 4He?

Key findings

• The lightest 4th-generation quark (U) can be metastable with a lifetime exceeding the age of the Universe if stabilized by a new U(1) gauge symmetry (y-charge), enabling cosmological relic production.
• U-hadrons such as (UUD)++ and (ŪŪŪ)--- can bind with 4He nuclei to form neutral, atom-like states, evading detection in terrestrial matter and avoiding constraints from anomalous isotope searches.
• In the case of charge symmetry, U-hadrons with +1 charge would overproduce anomalous hydrogen unless their lifetime is less than ~10^6 years, suggesting a narrow window for detectability in accelerators.
• For charge asymmetry, the excess of (meta)stable anti-up quarks of the 4th generation bound with 4He form a novel dark matter candidate with warm dark matter-like properties, catalyzing primordial heavy element production.
• Cosmic ray fluxes of +2 charged U-baryons and -2 charged anti-U-baryons could be detectable by PAMELA and AMS02, with fluxes at or below future experimental sensitivity levels.
• LHC experiments have good discovery potential for U-quarks with masses up to 1.5 TeV, especially via high-pT, low-velocity signals with charge-flipping effects in detectors.