Topological Leptogenesis

summary

The gist

The gist: Topological leptogenesis proposes a new mechanism to explain lepton asymmetry by introducing a gapped topological order sector that can cancel the baryon minus lepton (B − L) mixed

In short

Topological leptogenesis proposes a new mechanism for explaining lepton asymmetry by introducing a gapped topological order sector. This sector cancels the baryon minus lepton (B-L) mixed gauge-gravitational anomaly of the Standard Model. Dark matter arises from fractionalized excitations of this topological matter, and gravitational leptogenesis acts as an intermediate step.

Key concepts

Topological Leptogenesis: A new mechanism for generating lepton asymmetry using a hidden Beyond the Standard Model topological sector. This sector has a low-energy description governed by Topological Quantum Field Theory (TQFT) and topological order, allowing it to mediate the necessary particle decays.
Baryon minus Lepton Anomaly (B-L): A quantum anomaly in the Standard Model related to the continuous B minus L number symmetry. The paper suggests that a topological sector can cancel this mixed gauge-gravitational anomaly, which is crucial for generating the observed asymmetry.
Topological Order: A state of matter characterized by long-range entanglement and a gapped energy spectrum, often found in condensed matter systems. In this context, it describes the low-energy phase of the BSM sector that provides stable dark matter candidates.
Fractionalized Excitations (Anyons): Excitations above the topological order gap that possess fractionalized statistics, meaning they are neither standard bosons nor fermions. These anyon-like excitations can decay into Standard Model particles, contributing to the asymmetry generation.

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This episode discusses

The paper

Topological Leptogenesis · Read on arXiv

Juven Wang

London Institute for Mathematical Sciences · Center of Mathematical Sciences and Applications, Harvard University

In the standard lore, the baryon asymmetry of the present universe is attributed to the leptogenesis from the sterile right-handed neutrino with heavy Majorana mass decaying into the Standard Model's leptons at the very early universe -- called the Majorana fermion's leptogenesis; while the electroweak sphaleron causes baryogenesis at a later time. In this work, we propose a new mechanism, named topological leptogenesis, to explain the lepton asymmetry. Topological leptogenesis replaces some of the sterile neutrinos by introducing a new gapped topological order sector (whose low-energy exhibits topological quantum field theory with long-range entanglement) that can cancel the baryon minus lepton (B - L) mixed gauge-gravitational anomaly of the Standard Model. Then the Beyond-the-Standard-Model dark matter consists of topological quantum matter, such that the gapped non-particle excitations of extended line and surface defect with fractionalization and anyon charges can decay into the Standard Model particles. In addition, gravitational leptogenesis can be regarded as an intermediate step (between Majorana particle leptogenesis and topological non-particle leptogenesis) to mediate such decaying processes from the highly entangled gapped topological order excitations.

DOI: 10.1103/r763-lq1b

Transcript

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

Vera: I'm Vera.

Jocelyn: And I'm Jocelyn, here with Subrahmanyan.

Vera: Today's paper: "Topological Leptogenesis".

Jocelyn: The gist:

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

Paper summary: Vera: So to recap what we just heard about "Topological Leptogenesis," it's proposing a mechanism to explain lepton asymmetry by introducing a hidden Beyond-the-Standard-Model sector.

Jocelyn: They focus on this BSM topological sector, which is a Topological Quantum Matter sector whose low energy has Topological Quantum Field Theory, specifically in the sense of Schwarz-type Chern-Simons-Witten like theory.

Subrahmanyan: This topological order phase is at zero temperature and its excitations are fractionalized anyon like excitations with an energy E above the topological order gap, which they call DeltaTO.

Vera: These excitations, when their energy E is greater than or equal to the gap DeltaTO, can decay into Standard Model particles either through a topological discrete gauge interaction or via that mixed baryon minus lepton gauge-gravitational anomaly process.

Jocelyn: The core idea here is that this mechanism cancels the baryon minus lepton mixed gauge-gravitational anomaly of the Standard Model.

Subrahmanyan: They also point out that they prefer focusing on the U(one)Q minus NcL symmetry instead of just U(one)L because only that one has mixed anomaly-free with the Standard Model gauge group, while U(one)L alone does have a mixed anomaly with it, even though they are talking about lepton number violation <ref:2501.00607#pg1>.

Vera: So, to sum up the thesis of "Topological Leptogenesis," it's replacing some of the sterile neutrinos by this gapped topological order sector that cancels that mixed gauge-gravitational anomaly.

Jocelyn: And then, as a consequence, the Beyond-the-Standard-Model dark matter is actually this topological quantum matter itself.

Subrahmanyan: The paper connects this to how gravitational leptogenesis acts as an intermediate step between the Majorana particle leptogenesis and this topological non-particle leptogenesis.

Vera: It’s essentially suggesting that we might need these new topological sectors to handle the quantum anomalies in a way that makes the math consistent with what we see in our universe.

Jocelyn: So, it moves away from just having heavy sterile neutrinos as the sole source of asymmetry and introduces this entire topological structure.

Conclusion: Vera: So, looking at the whole paper "Topological Leptogenesis," the authors are proposing this new mechanism to explain lepton asymmetry through a topological sector.

Jocelyn: They argue that this approach deals with the quantum anomalies in a way that is consistent with Standard Model gauge groups.

Subrahmanyan: It seems like they are trying to find a way where you don't have to rely solely on heavy sterile neutrinos for baryogenesis or lepton asymmetry generation.

Vera: The paper suggests that this model introduces a new gapped topological order sector, and its dark matter candidate is this topological quantum matter.

Jocelyn: They also highlight the connection to gravitational leptogenesis as a possible bridge between different types of leptogenesis scenarios.

Subrahmanyan: It’s interesting because they are linking the structure of the Standard Model anomalies to a specific type of quantum field theory in five dimensions, which they call an invertible topological field theory.

Vera: The implication for us is that if this mechanism is correct, we need to look for experimental signatures from this topological matter.

Jocelyn: Because as the authors say, you can't just assume these mechanisms are working without looking for evidence in the lab or in space.

Subrahmanyan: So, the main point here is that this paper offers an alternative scenario to resolve some of the challenges presented by other leptogenesis models.

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