Implications of tachyonic phase transition in classically scale invariant general U(1) X models

summary

The gist

The gist: Gravitational waves from tachyonic phase transitions in classically scale-invariant general U(1)X models can probe regions with small gauge couplings and heavy Z′ bosons that are

In short

The study explores gravitational wave (GW) signals from a 'tachyonic phase transition' in a specific theoretical model called the classically scale-invariant U(1)X extension of the Standard Model. This model involves new gauge bosons and neutrinos. The research shows that GWs can probe regions with small gauge couplings and heavy Z' bosons, demonstrating how gravitational wave observations complement traditional collider searches.

Key concepts

U(1)X Extension: This is a theoretical extension of the Standard Model that adds a new symmetry, U(1X). It introduces extra particles like right-handed neutrinos and a new gauge boson called Z'. The model is designed to be classically scale-invariant, meaning its fundamental parameters are not fixed at the beginning.
Tachyonic Phase Transition: This describes a specific type of phase transition where the effective potential for a scalar field becomes unstable, leading to an inhomogeneous excitation. This instability generates fluctuations in the scalar field that can produce a characteristic stochastic gravitational wave background signal during the transition.
Complementarity of Probes: This concept highlights how different experimental methods, like particle colliders (LEP, LHC) and gravitational wave observatories (LISA, DECIGO), can test the same underlying physics in different ways. The paper demonstrates that GWs can reach parameter spaces inaccessible to colliders, showing their complementary nature.

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This episode discusses

The paper

Implications of tachyonic phase transition in classically scale invariant general U(1) X models · Read on arXiv

Arindam Das a,b Katsuya Hashino c Yuta Orikasa d Masanori Tanaka e

Institute for Academic Innovation, Hokkaido University · Department of Physics, Hokkaido University · National Institute of Technology, Fukushima College · Institute of Experimental and Applied Physics, Czech Technical University in Prague · Center for High Energy Physics, Peking University

We investigate the complementarity between collider searches and gravitational-wave (GW) observations in the classically scale-invariant general U(1) X extension of the Standard Model. The U(1) X scale is generated radiatively through the Coleman-Weinberg mechanism, while the electroweak scale is induced through the Higgs portal, without explicit mass terms in the scalar potential. Three right-handed neutrinos are introduced to ensure anomaly cancellation and acquire Majorana masses upon U(1) X symmetry breaking, which also generates the mass of the neutral gauge boson Z'. In the strongly supercooled regime, a tachyonic U(1) X phase transition can produce a stochastic GW background. Assuming three heavy Majorana neutrinos, we study their effects on the phase-transition dynamics and reheating, and estimate the resulting GW signals. We identify the regions of the U(1) X gauge coupling and Z' mass accessible to future GW observatories, including LISA and DECIGO, and compare them with existing LEP and LHC constraints. We find that GWs from tachyonic phase transitions can probe regions with small gauge couplings and heavy Z' bosons that are difficult to access through collider searches, demonstrating the complementarity of these probes.

Transcript

Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: Today's paper: "Implications of tachyonic phase transition in classically scale invariant general U(1) X models".

Jocelyn: The gist:

Vera: First, who's behind it and why it matters.

Paper summary: Vera: To recap what we just covered, the paper "Implications of tachyonic phase transition in classically scale invariant general U(one X models" explores how gravitational waves from a tachyonic phase transition can be detected by looking at the U(one X gauge coupling and Z prime mass <ref:2610.11192#pg1,Implications of tachyonic phase transition in classically scale invariant general U(1>.

Jocelyn: It sets out that this specific model has its U(one X scale generated radiatively through the Coleman-Weinberg mechanism, and the electroweak scale comes from a Higgs portal coupling <ref:2610.11192#pg1,generated radiatively through the Coleman-Weinberg mechanism>.

Subrahmanyan: They introduce three right-handed neutrinos to ensure anomaly cancellation, and these neutrinos acquire Majorana masses upon U(one X symmetry breaking, which also generates the mass of the neutral gauge boson Z prime <ref:2610.11192#pg1>.

Vera: The core focus is on the phase transition dynamics, suggesting that in this setup, there's a possibility that the U(one X phase transition can occur after the QCD phase transition <ref:2610.11192#pg1>.

Jocelyn: If that happens, it implies all quarks don't get their current masses before U(one X breaks, which suggests the QCD phase transition would be first-order <ref:2610.11192#pg1>.

Subrahmanyan: The paper also discusses a new kind of phase transition called the tachyonic phase transition, which can happen if the U(1B-L and EW symmetry breaking aren't induced even after the QCD phase transition <ref:2610.11192#pg1>.

Vera: During this tachyonic phase transition, an inhomogeneous scalar field excitation forms, and its dynamics might leave a characteristic stochastic gravitational wave signal.

Jocelyn: The connection to gravitational waves comes from the tensor perturbation carried out by that inhomogeneous scalar field formed during the tachyonic phase transition.

Subrahmanyan: The spatial part of the scalar energy-momentum tensor is written as Tij = partial i phi partial j phi plus delta ij one/two phi dot squared minus one/two a squared (nabla phi) squared minus Veff(phi) <ref:2610.11192#pg2>.

Vera: Since PiTTij is quadratic in terms of delta phi which gets exponentially amplified during the tachyonic phase transition, the GW source is enhanced much faster than the scalar mode functions themselves.

Jocelyn: The peak frequency at production, f star, is set by the characteristic scale of those scalar inhomogeneities, estimated as f star ∼ k star a star ∼ delta m QCD.

Conclusion: Vera: So to wrap up this discussion on "Implications of tachyonic phase transition in classically scale invariant general U(one X models," we're talking about how this model links the physics we see in particle accelerators to what telescopes can detect with gravitational waves <ref:2610.11192#pg1,Implications of tachyonic phase transition in classically scale invariant general U(1>.

Jocelyn: The paper shows that GWs from these tachyonic phase transitions can probe regions with small gauge couplings and heavy Z prime bosons that are hard for collider searches to access, which is a demonstration of complementarity.

Subrahmanyan: Specifically, if the mass of the new gauge boson Z prime and the U(one X gauge coupling are between one hundred six GeV and one hundred seven GeV for mZ prime and between zero point zero zero one and zero point two five for gX, then DECIGO might test that GW signal.

Vera: And the paper also points out that in the parameter region where gX is greater than zero point two five, you can explore those signals by observing gravitational waves produced by vacuum bubbles nucleated by first-order phase transitions.

Jocelyn: This means that the complementarity between colliders and GW observations is useful for testing this model thoroughly, showing how these two probes work together to explore different parameter spaces.

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