Utilizing gravitational-wave (GW) lensing opens a new way to understand the small-scale structure of the universe. We show that, in spite of its coarse angular resolution and short duration of observation, LIGO can detect the GW lensing induced by compact structures, in particular by compact dark matter (DM) or primordial black holes of 10 − 10 5 M , which remain interesting DM candidates. The lensing is detected through GW frequency chirping, creating the natural and rapid change of lensing patterns: frequency-dependent amplification and modulation of GW waveforms. As a highest-frequency GW detector, LIGO is a unique GW lab to probe such light compact DM. With the design sensitivity of Advanced LIGO, one-year observation by three detectors can optimistically constrain the compact DM density fraction fDM to the level of a few percent.Introduction. The GW from far-away binary mergers [1, 2] is a new way to see the universe with gravitational interaction. Not only is it revealing astrophysics of solar-mass black holes and neutron stars, but the GW can also carry information of intervening masses and the evolution of the universe through gravitational lensing. Having the long wavelength λ, the GW is usually expected to be lensed by heaviest structures (such as galaxies and their clusters) with large enough Schwarzschild radii, 2GM/c 2 = 2M λ 2 × 10 3 (100 Hz/f ) M . Their prototypical lensing signal is strongly time-delayed GW images [3,4] or statistical correlations [5].

If the mass of dark matter is generated from a cosmological phase transition involving the nucleation of bubbles, the corresponding bubble walls can filter out dark matter particles during the phase transition. Only particles with sufficient momentum to overcome their mass inside the bubbles can pass through the walls. As a result, the dark matter number density after the phase transition has a suppression factor expð−M χ =2γTÞ, where M χ is the dark matter mass, andγ and T are the Lorentz factor and temperature of the incoming fluid in the bubble wall rest frame, respectively. Under certain assumptions, we show that the filtering-out process can naturally provide a large suppression consistent with the observed dark matter density for a wide range of dark matter masses up to the Planck scale. Since the first-order phase transition is the decisive ingredient in our mechanism, a new connection is made between heavy dark matter scenarios and gravitational wave observations.

In the context of Twin Higgs models, we study a simple mechanism that simultaneously generates asymmetries in the dark and visible sector through the out-of-equilibrium decay of a TeV scale particle charged under a combination of baryon and twin baryon number. We predict the dark matter to be a 5 GeV twin baryon, which is easy to achieve because of the similarity between the two confinement scales. Dark matter is metastable and can decay to three quarks, yielding indirect detection signatures. The mechanism requires the introduction of a new colored particle, typically within the reach of the LHC, of which we study the rich collider phenomenology, including prompt and displaced dijets, multi-jets, monojets and monotops.

We examine the large volume compactification of Type IIB string theory or its F theory limit and the associated supersymmetry breakdown and soft terms. It is crucial to incorporate the loop-induced moduli mixing, originating from radiative corrections to the Kähler potential.We show that in the presence of moduli mixing, soft scalar masses generically receive a D-term contribution of the order of the gravitino mass m 3/2 when the visible sector cycle is stabilized by the D-term potential of an anomalous U(1) gauge symmetry, while the moduli-mediated gaugino masses and A-parameters tend to be of the order of m 3/2 /8π 2 . It is noticed also that a too large moduli mixing can destabilize the large volume solution by making it a saddle point. * In this picture, the uplifting potential is exponentially small as it arises from a SUSY breakdown at the tip of warped throat, and then small W 0 is required to tune the cosmological constant to a nearly vanishing value.Planck discussed in [8]. We also stress the importance of the D-terms along the visible sector 4-cycle in the LVS-models. They tend to dominate the soft scalar mass terms and give a contribution of the order of the gravitino mass m 3/2 . Gaugino masses and A-parameters do not receive D-term contributions, and generically tend to be loopsuppressed, being of the order of O(m 3/2 /8π 2 ). With these contributions from moduli mixings, if the gravitino mass were of the order of 10 11 GeV as conjectured in [8] (in order to accommodate the unification scale M GU T ∼ 10 16 GeV with W 0 ∼ O(1)), severe fine-tuning of the Kähler potential at the multi-loop level would be required to keep the soft terms in the TeV range.We would therefore argue that the gravitino mass should not exceed the (multi)-TeV range. This paper is organized as follows. In section 2, we revisit the LVS-scheme while incorporating the moduli redefinition discussed in [9]. We also include a discussion of the stability of the large volume solution in the presence of moduli mixing. Section 3 discusses the D-term stabilization of the visible sector cycle with an explicit scheme to stabilize the remained D-flat direction which is parameterized in this case by U(1) A -charged (but MSSM singlet) matter fields breaking a global Peccei-Quinn symmetry spontaneously. This scheme naturally generates an intermediate axion scale in LVS, and can be implemented in other scenarii with a high string scale close to the Planck scale. Section 4 is devoted to the discussion of supersymmtry breakdown and resulting soft terms, and conclusions and outlook will be given in section 5.

The axion is a light pseudoscalar particle postulated to solve issues with the Standard Model, including the strong CP problem and the origin of dark matter. In recent years, there has been remarkable progress in the physics of axions in several directions. An unusual type of axion-like particle termed the relaxion was proposed as a new solution to the weak scale hierarchy problem. There are also new ideas for laboratory, astrophysical, or cosmological searches for axions; such searches can probe a wide range of model parameters that were previously inaccessible. On the formal theory side, the weak gravity conjecture indicates a tension between quantum gravity and a trans-Planckian axion field excursion. Many of these developments involve axions with hierarchical couplings. In this article, we review recent progress in axion physics, with particular attention paid to hierarchies between axion couplings. We emphasize that the parameter regions of hierarchical axion couplings are the most accessible experimentally. Moreover, such regions are often where important theoretical questions in the field are addressed, and they can result from simple model-building mechanisms. Expected final online publication date for the Annual Review of Nutrition, Volume 41 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The dS swampland conjecture |∇V |/V ≥ c, where c is presumed to be a positive constant of order unity, implies that the dark energy density of our Universe can not be a cosmological constant, but mostly the potential energy of an evolving quintessence scalar field. As the dark energy includes the effects of the electroweak symmetry breaking and the QCD chiral symmetry breaking, if the dS swampland conjecture is applicable for the low energy quintessence potential, it can be applied for the Higgs and pion potential also. On the other hand, the Higgs and pion potential has the well-known dS extrema, and applying the dS swampland conjecture to those dS extrema may provide stringent constraints on the viable quintessence, as well as on the conjecture itself. We examine this issue and find that the pion dS extremum at cos(π 0 /f π ) = −1 implies c O(10 −2 − 10 −5 ) for arbitrary form of the quintessence potential and couplings, where the weaker bound (10 −2 ) is available only for a specific type of quintessence whose couplings respect the equivalence principle, while the stronger bound (10 −5 ) applies for generic quintessence violating the equivalence principle. We also discuss the possibility to relax this bound with an additional scalar field, e.g. a light modulus which has a runaway behavior at the pion dS extremum. We argue that such possibility is severely constrained by a variety of observational constraints which do not leave a room to significantly relax the bound. We make a similar analysis for the Higgs dS extremum at H = 0, which results in a weaker bound on c. * Electronic address: kchoi@ibs.re.kr † Electronic address:

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Abstract:The continuum clockwork is an extra-dimensional set-up to realize certain features of the clockwork mechanism generating exponentially suppressed or hierarchical couplings of light particles. We study the continuum clockwork in a general scheme in which large volume, warped geometry, and localization of zero modes in extra dimension are described by independent parameters. For this, we propose a generalized 5-dimensional linear dilaton model which can realize such set-up as a solution of the model, and examine the KK spectrum and the couplings of zero modes and massive KK modes to boundarylocalized operators for the bulk graviton, Abelian gauge bosons and periodic scalar fields. We discuss how those KK spectra and couplings vary as a function of the volume, warping and localization parameters, and highlight the behavior in the parameter region corresponding to the clockwork limit. We discuss also the field range of 4-dimensional axions originating from either 5-dimensional periodic scalar field or the 5-th component of an Abelian gauge field, and comment on the limitations of continuum clockwork compared to the discrete clockwork.