Physics Letters B 802 (2020) 135258
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Physics Letters B
www.elsevier.com/locate/physletb
Dark matter, dark photon and superfluid He-4 from effective field
theory
Andrea Caputo
a
, Angelo Esposito
b,∗
, Emma Geoffray
b
, Antonio D. Polosa
c
, Sichun Sun
c
a
Instituto de Fisica Corpuscular, Universidad de Valencia and CSIC, Edificio Institutos Investigacion, Catedratico Jose Beltran 2, Paterna, 46980 Spain
b
Theoretical Particle Physics Laboratory (LPTP), Institute of Physics, EPFL, 1015 Lausanne, Switzerland
c
Dipartimento di Fisica and INFN, Sapienza Università di Roma, P.le Aldo Moro 2, I-00185 Roma, Italy
a r t i c l e i n f o a b s t r a c t
Article history:
Received
14 November 2019
Received
in revised form 11 January 2020
Accepted
23 January 2020
Available
online 27 January 2020
Editor: A.
Ringwald
Keywords:
Light
dark matter
Effective
theory
Helium
Phonon
Dark
photon
We consider a model of sub-GeV dark matter whose interaction with the Standard Model is mediated
by a new vector boson (the dark photon) which couples kinetically to the photon. We describe the
possibility of constraining such a model using a superfluid He-4 detector, by means of an effective theory
for the description of the superfluid phonon. We find that such a detector could provide bounds that
are competitive with other direct detection experiments only for ultralight vector mediator, in agreement
with previous studies. As a byproduct we also present, for the first time, the low-energy effective field
theory for the interaction between photons and phonons.
© 2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
1. Introduction
To understand the origin and nature of dark matter has been
a central topic in both theoretical and experimental physics for a
long time. In particular, if considered as a new kind of particle,
the presence of dark matter would constitute one of the strongest
evidences for physics beyond the Standard Model. A large share of
the efforts so far has been devoted to the study of the so-called
Weakly Interacting Massive Particle, i.e. dark matter particles with
masses of order 100 GeV and interaction strengths comparable to
the weak interactions. These searches did not lead to any positive
result, yet.
This
provides a strong motivation to look into different mass
regions, and several efforts have been devoted to the study of
sub-GeV dark matter, as proposed by different models — see
e.g. [1–14]. To detect such particles experimentally one needs de-
vices
with energy thresholds below the eV, and several propos-
als
have been put forth, ranging from superconductors [15–17],
polar materials [18–20], Dirac materials [21–23], and many oth-
ers [24–36].
Among
these, the concept of employing a detector based on
superfluid He-4 was first presented in [37–39], and then further
*
Corresponding author.
E-mail
address: angelo.esposito@epfl.ch (A. Esposito).
developed in [40–43]. In particular, the interaction of the dark
matter with the bulk of the detector can produce collective excita-
tions,
which could then be detected [44,45], allowing a sensitivity
to dark matter as light as the keV. If the dark matter interacts with
the Standard Model via a scalar mediator, such a detector could
provide very promising bounds. In [42,43]the problem has been
formulated in terms of a relativistic effective field theory (EFT) for
superfluids [46–48], which allows to describe the interactions of
the He-4 phonon with itself and with the dark matter in a simple
way, starting from a standard action principle. Such an approach
has already been proved to be successful in a number of phe-
nomenological
applications — see e.g. [49–54].
In
this paper we continue this program by studying the case of
a sub-GeV dark matter charged under some new U
d
(1) group and
interacting with the Standard Model via a new vector mediator
(the dark photon) which mixes kinetically with the photon [55,56].
To
this end, we write down the most general relativistic low-
energy
EFT for the interaction between the photon and the bulk
of He-4 which, to the best of our knowledge, appears here for the
first time. With this at hand, we study the process of emission of
a single phonon by the passing dark matter and discuss the result
in the context of the present direct, cosmological and astrophysical
constraints for the dark photon mass and coupling. In agreement
with [41], we find that a He-4 detector could be competitive with
the current bounds for ultra-light dark photons.
https://doi.org/10.1016/j.physletb.2020.135258
0370-2693/
© 2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by
SCOAP
3
.