Precision studies of scattering processes at colliders provide powerful indirect constraints on new physics. We study the helicity structure of scattering amplitudes in the SM and in the context of an effective Lagrangian description of BSM dynamics. Our analysis reveals a novel set of helicity selection rules according to which, in the majority of 2 → 2 scattering processes at high energy, the SM and the leading BSM effects do not interfere. In such situations, the naive expectation that dimension-6 operators represent the leading BSM contribution is compromised, as corrections from dimension-8 operators can become equally (if not more) important well within the validity of the effective field theory approach.

Conventional approaches to probing axions and axion-like particles (ALPs) typically rely on a coupling to photons. However, if this coupling is extremely weak, ALPs become invisible and are effectively decoupled from the Standard Model. Here we show that such invisible axions, which are viable candidates for dark matter, can produce a stochastic gravitational wave background in the early universe. This signal is generated in models where the invisible axion couples to a dark gauge boson that experiences a tachyonic instability when the axion begins to oscillate. Incidentally, the same mechanism also widens the viable parameter space for axion dark matter. Quantum fluctuations amplified by the exponentially growing gauge boson modes source chiral gravitational waves. For axion decay constants f 10 17 GeV, this signal is detectable by either pulsar timing arrays or space/ground-based gravitational wave detectors for a broad range of axion masses, thus providing a new window to probe invisible axion models.

It is well known that in noncentral heavy-ion collisions a transient strong magnetic field is generated in the direction perpendicular to the reaction plane. The maximal strength of this field is estimated to be $eB \sim m^2_{\pi} \sim 0.02 \text{GeV}^2$ at the RHIC and $eB \sim 15 m^2_{\pi} \sim 0.3 \text{GeV}^2$ at the LHC. We investigate the effects of a strong magnetic field on $B$ and $D$ mesons, focusing on the changes of the energy levels and the masses of the bound states. Using the Color Evaporation Model we discuss the possible changes in the production of $J/\psi$ and $\Upsilon$.Comment: 18 pages, 7 figure

In this paper, we extend the well-known QCD sum rules used in the calculation of the mass of heavy mesons to estimate the modification of the charged B-meson mass, m B , in the presence of an external Abelian magnetic field, eB. Two simplifying limits were considered: the weak field limit, in which the external field satisfies eB ≪ m 2 (with m being any of the masses involved); and the strong field limit, in which the field strength is small in comparison to the bottom quark mass (or the B-meson mass) squared, but it is large compared to the mass of the light quarks, i.e., m 2 u;d ≪ eB ≪ m 2 b;B . We found that m B decreases with the magnetic field in both of these limits.