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We conduct a comprehensive study on the sub-GeV millicharge dark matter produced through the freeze-in mechanism. We discuss in general the mixing mechanism, encompassing both kinetic mixing and mass mixing, between the $U(1)_X$ hidden…
The Higgs boson mass may arise from a portal coupling to a singlet field $\sigma$ which has a very large VEV $f \gg m_\text{Higgs}$. This requires a sector of "ultra-weak" couplings $\zeta_i$, where $\zeta_i \lesssim m_\text{Higgs}^2 /…
We argue that the lightest vector bound states of a confining hidden sector communicating with the Standard Model through the Higgs portal are stable and are viable candidates of dark matter. The model is based on an SU(2) gauge group with…
The scalar potential of the Minimal Supersymmetric Standard Model (MSSM) admits the existence of vacua with non-vanishing expectation values of electrically and color charged fields. If such minima are deep enough, the physical electroweak…
The effective field theory of dark energy is generalized to incorporate dark matter, which is modelled using a complex scalar field with a global $U(1)$ symmetry. The dark matter model used here has similarities to models of ultralight…
The standard model of elementary particles (SM), despite experimental completion at the LHC, needs to be extended for various physical reasons, including the cold dark matter (DM). Each extension comes with its scale and mechanism, and…
We discuss the parameter space of the Inert Doublet Model, a two Higgs doublet model with a dark matter candidate. An extensive set of theoretical and experimental constraints on this model is considered, where both collider as well as…
We investigate a dark sector coupled to the Standard Model (SM) through a kinetically mixed dark photon $U$ associated with a new $U(1)'$ gauge symmetry. Kinetic mixing $\varepsilon$ induces an effective coupling to the electromagnetic…
Dark sector may exist and interact with Standard Model (SM) through the $U(1)$ kinetic mixing. Through this portal-type interaction, dark photon from dark sector couples to SM fermions, and may explain the discrepancy between experimental…
We consider a two-Higgs doublet scenario containing three $SU(2)_L$ singlet heavy neutrinos with Majorana masses. The second scalar doublet as well as the neutrinos are odd under a $Z_2$ symmetry. This scenario not only generates Majorana…
Light scalar fields can naturally couple disformally to matter fields. Static, non-relativistic sources do not generate a classical field profile for a disformally coupled scalar, and so such scalars are free from the constraints on the…
We study supersymmetric scenarios where the dark matter is the gaugino of an unbroken hidden U(1) which interacts with the visible world only via a small kinetic mixing with the hypercharge. Strong constraints on the parameter space can be…
Starting from the previously constructed effective supergravity theory below the scale of U(1) breaking in orbifold compactifications of the weakly coupled heterotic string, we study the effective theory below the scale of supersymmetry…
We consider candidates for dark matter in models of gauge mediated supersymmetry breaking, in which the supersymmetry breaking sector is weakly coupled and calculable. Such models typically contain classically flat directions, that receive…
In a previous paper it was shown that a minimally coupled scalar field of mass $M \sim H_0$ can describe both components of the dark sector in a unified way. In the solution found, the dark energy component decays linearly with the Hubble…
Tiny values for gauge couplings of dark photons allow to suppress their kinetic mixing with ordinary photons. We point out that the Weak Gravity Conjecture predicts consequently low ultraviolet cut-offs where new degrees of freedom might…
Asymmetric symmetry breaking models dynamically break the G X G gauge symmetries of mirror models to distinct subgroups in the two sectors. The coincidental abundances of visible and dark matter, $\Omega_{DM} \simeq 5\Omega_{VM}$, motivates…
We explore the feasibility and astrophysical consequences of a new long-range U(1) gauge field ("dark electromagnetism") that couples only to dark matter, not to the Standard Model. The dark matter consists of an equal number of positive…
We study several aspects of supersymmetric models with a $U(1)_R$ symmetry where the Higgs doublet is identified with the superpartner of a lepton. We derive new, stronger bounds on the gaugino masses based on current measurements, and also…
In the presence of large extra dimensions, the fundamental Planck scale can be much lower than the apparent four-dimensional Planck scale. In this setup, the weak gravity conjecture implies a much more stringent constraint on the UV cutoff…