Dark matter and naturalness

Abstract

The Standard Model of particle physics is governed by Poincaré symmetry, while all other symmetries, exact or approximate, are essentially dictated by theoretical consistency with the particle spectrum. On the other hand, many models of dark matter exist that rely upon the addition of new added global symmetries in order to stabilize the dark matter particle and/or achieve the correct abundance. In this work we begin a systematic exploration into truly natural models of dark matter, organized by only relativity and quantum mechanics, without the appeal to any additional global symmetries, no fine-tuning, and no small parameters. We begin by reviewing how singlet dark sectors based on spin 0 or spin 1 2 should readily decay, while pure strongly coupled spin 1 models have an overabundance problem. This inevitably leads us to construct chiral models with spin 1 2 particles charged under confining spin 1 particles. This leads to stable dark matter candidates that are analogs of baryons, with a confinement scale that can be naturally O(100)TeV. This leads to the right freeze-out abundance by annihilating into massless unconfined dark fermions. The minimal model involves a dark copy of SU (3) × SU (2) with 1 generation of chiral dark quarks and leptons. The presence of massless dark leptons can potentially give rise to a somewhat large value of ∆N eff during BBN. In order to not upset BBN one may either appeal to a large number of heavy degrees of freedom beyond the Standard Model, or to assume the dark sector has a lower reheat temperature than the visible sector, which is also natural in this framework. This reasoning provides a robust set of dark matter models that are entirely natural. Some are concrete realizations of the nightmare scenario in which dark matter may be very difficult to detect, which may impact future search techniques. *

Glueball scattering cross section in lattice SU(2) Yang-Mills theory

“…In this section, we shall show that the glueball DM is very natural among composite DM scenarios [241][242][243][244][245]251,253,266, and dark gauge theories. The assumption of the existence of dark gauge sectors is indeed a reasonable answer to the problem of the ad hoc gauge group of the SM, since they may naturally arise in many contexts such as in string or grand unification theories [236,237,245,[255][256][257][258][259][260][261][262][263][264][265][266].…”

“…In this context, an additional Yang-Mills theory (YMT), which does not or very weakly interacts with the SM particles, is an attractive candidate, since the lightest particle of the spectrum is a glueball , fulfilling the conditions required for being DM [236][237][238][239][240][241][242][243][244][245][246][247][248][249][250][251][252][253][254]. This "dark" YMT may naturally be generated in grand unification frameworks [236,237,245,[255][256][257][258][259][260][261][262][263][264][265][266], and it is possible to experimentally detect them by observing the gravitational wave background [246,[267][268][269][270][271][272][273][274][275][276][277]...…”

Chiral Symmetry and the Cosmological Constant

“…In particular, this opens the possibility of confinement, such that dark matter today is in the form of dark baryons. This idea has been explored in, e.g., [20,21]. With primordial baryons, the cosmological evolution is similar that of the "superheavy dark matter" scenario [42,43,44,45,46,47,48]: the primordial abundance of dark matter redshifts like matter, such that the number of particles per Hubble volume grows with the scale factor during radiation domination, and can provide all the dark matter in the universe today.…”

“…A simple scenario for dark matter that can arise in this way is a model of dark baryons, see e.g. [20,21].…”

Composite dark matter from strongly-interacting chiral dynamics

“…Models of this kind with DM candidates appeared for example in refs. [25][26][27]. In this class of theories the masses of all the dark states are generated dynamically, since no fermion mass term is allowed by gauge invariance.…”