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.
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:
Any particle that is charged under SU (3) C and U (1) EM can mediate the gg → γγ process through loops. Near the threshold for the new particle pair production, gauge boson exchanges necessitate the resummation of ladder diagrams. We discuss the leading log order matching of the one-loop result with non-relativistic effective theory resummed result. We show how the diphoton invariant mass spectrum varies depending on decay width, color representation and electric charge of the new particle. The exclusion limits on the product of SU (3) C and U (1) EM charges of the new scalar or fermion particle are obtained from current LHC data. *
Any new particle charged under SU (3)C and carrying electric charge will leave an imprint in the di-photon invariant mass spectrum as it can mediate gg → γγ process through loops. The combination of properties of loop functions, threshold resummation and gluon pdfs can result in a peak-like feature in the di-photon invariant mass around twice the mass of a given particle even if the particle is short-lived and thus it doesn't form a narrow bound state. Using recent ATLAS analysis, we set upper limits on the combined SU (3)C and electric charge of new particles and indicate future prospects. We also discuss the possibility that the excess of events in the di-photon invariant mass spectrum around 750 GeV originates from loops of a particle with mass around 375 GeV.Introduction. As demonstrated by discoveries of the Z boson and the Higgs boson, a resonance is the cleanest signal of a new particle as long as its branching ratios to visible modes are nonzero. However, many popular models including minimal supersymmetric standard model or models with various top-partners predict particles that can be produced in pairs. For the pair production, the searches highly depend on decay modes of a given particle and there are known scenarios in well motivated models which are difficult to see directly even if production cross sections are sizable. In principle, a model can always be constructed in which a new particle cascade decays to complex final states consisting of soft particles and possibly missing energy, or the particle has a large number of possible final states with small branching ratios to individual ones. Signatures that are less model dependent or do not depend on decay modes at all are therefore an integral part of searches for new physics.
We discuss an extension of the standard model by fields not charged under standard model gauge symmetry in which the electroweak symmetry breaking is driven by the Higgs quartic coupling itself without the need for a negative mass term in the potential. This is achieved by a scalar field S with a large coupling to the Higgs field at the electroweak scale which is driven to very small values at high energies by the gauge coupling of a hidden symmetry under which S is charged. This model can remain perturbative all the way to the Planck scale. The Higgs boson is fully standard-model-like in its couplings to fermions and gauge bosons. However, the effective cubic and quartic self-couplings of the Higgs boson are significantly enhanced.
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