A scalar-extended U(1) L mu-L tau explanation of the LUX-ZEPLIN 248 keV excess

summary

Video file (mp4)

The gist

The gist The recently observed dark matter (DM) nuclear recoil event at an energy of 248 ± 23 (stat.) ± 23 (syst.) keV at the LUX-ZEPLIN (LZ) experiment, favoring an inelastic scattering

In short

The paper proposes extending a U(1)Lµ-Lτ model with two complex scalar fields, $\Phi$ and $S$, to explain a 248 keV dark matter nuclear recoil event at LZ. This extension introduces a trilinear interaction that generates the necessary mass splitting between DM particles, leading to an inelastic scattering scenario that matches the observed excess.

Key concepts

U(1)L$\mu$-L$\tau$ Model
This is a theoretical framework based on an extended gauge symmetry ($U(1)$) involving lepton number conservation related to muons and taus. It introduces new interactions mediated by a gauge boson, $Z_{\mu\tau}$, which couples to these leptons, serving as the mediator for the dark matter interaction.
Inelastic DM Scattering
This describes a specific type of dark matter interaction where the incoming DM particle scatters inelastically with a nucleus. In this model, it arises because there is a mass splitting ($\delta m$) between two scalar fields, allowing for energy exchange during the scattering process.
Scalar Sector Dynamics
The model introduces two new complex scalar fields, $\Phi$ and $S$, with specific charges under the gauge symmetry. The spontaneous breaking of this symmetry by $S$ generates a mass for the new gauge boson ($Z_{\mu\tau}$) and causes a mass splitting between the real and imaginary parts of $\Phi$, which is key to generating the DM mass difference.

Terminology used across episodes

This episode discusses

The paper

A scalar-extended U(1) L mu-L tau explanation of the LUX-ZEPLIN 248 keV excess · Read on arXiv

Dipankar Pradhan, Abhik Sarkar

Institute of Physics, Sachivalaya Marg, Bhubaneswar, Odisha · Homi Bhabha National Institute, BARC Training School Complex, Mumbai · Laboratoire de Physique Subatomique et de Cosmologie, Université Grenoble-Alpes

The recently observed dark matter (DM) nuclear recoil event at an energy of 248 plus or minus 23,(stat.) plus or minus 23,(syst.), keV at the LUX-ZEPLIN (LZ) experiment, favoring an inelastic scattering interpretation, has motivated various beyond the Standard Model (BSM) scenarios aimed at explaining the observed excess. In particular, this provides an opportunity to probe models that naturally accommodate inelastic DM scattering. In this work, we explore one such possibility by extending the U(1) L μ-L τ model with two complex scalar fields, Φ and S, carrying charges-1 and +2, respectively, under the U(1) L μ-L τ gauge symmetry. These charge assignments allow a trilinear interaction between the two scalar fields, which is crucial for generating the DM mass splitting. Following the spontaneous breaking of the U(1) L μ-L τ symmetry, with S acquiring a vacuum expectation value and generating a mass for the BSM gauge boson Z μτ, the real and imaginary components of Φ acquire a mass splitting. This naturally gives rise to an inelastic DM scattering scenario that can accommodate the LZ excess. We perform a likelihood-based assessment of the sensitivity of the model parameters to the observed event while consistently accounting for other relevant phenomenological constraints. Finally, we discuss the prospects for probing the viable parameter space at future experiments.

Transcript

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

Vera: Today's paper: "A scalar-extended U(1) L mu-L tau explanation of the LUX-ZEPLIN 248 keV excess".

Jocelyn: The gist The recently observed dark matter (DM) nuclear recoil event at an energy of 248 ± 23 (stat.) ± 23 (syst.) keV at the LUX-ZEPLIN (LZ) experiment,

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

Paper summary: Vera: So, what this paper is claiming is that this specific setup—the scalar-extended U(one) L mu-L tau model—provides a way to generate the mass splitting needed for that two hundred forty-eight keV recoil <ref:2610.12443#pg1>.

Jocelyn: They are proposing two complex scalars, and S, with charges-one and +two respectively, under the U(one) L mu-L tau symmetry <ref:2610.12443#pg1,charges $-1$ and $+2$, respectively, under the U(1>.

Subrahmanyan: The motivation is that this specific charge assignment allows for a trilinear interaction between these two scalars, which is key to generating the DM mass splitting.

Vera: Once the symmetry breaks because S gets a vacuum expectation value, it creates a massive gauge boson called Z mu tau, and this process also splits the masses of 's components.

Jocelyn: This mass splitting is what leads to the inelastic DM scattering that they claim can account for the LZ excess.

Subrahmanyan: They also point out that this U(one) L mu-L tau model has other signatures, like tree-level couplings of Z mu tau to muons and taus <ref:2610.12443#pg1>.

Vera: But they mention a big caveat: couplings to other Standard Model fermions only appear at the one-loop level, which suppresses those constraints.

Conclusion: Vera: So, looking at the title, "A scalar-extended U(one) L mu-L tau explanation of the LUX-ZEPLIN two hundred forty-eight keV excess," it’s clear they are connecting a specific particle model to a concrete observation in dark matter direct detection <ref:2610.12443#pg1,explanation of the LUX-ZEPLIN 248 keV excess>.

Jocelyn: They are taking the LZ event and trying to build a mechanism, using these extra scalar fields, to explain the energy of that recoil through inelastic scattering.

Subrahmanyan: The implication is that if this model works, it tells us something fundamental about how dark matter interacts with ordinary matter in a way that goes beyond simple elastic scattering.

Vera: It suggests we should look for these specific types of interactions in future experiments because the parameter space they've identified still has room to be explored.

Jocelyn: They conclude that this framework gives a well-motivated realization of inelastic dark matter, where the scalar sector naturally provides the small mass splitting required for that observed recoil.

Subrahmanyan: The paper suggests this is a promising avenue for testing whether dark matter has properties beyond what we see in simple elastic scattering scenarios.

More episodes

← Home