Third Family Quark-Lepton Unification at the TeV Scale

We construct a model of quark-lepton unification at the TeV scale based on an $SU(4)$ gauge symmetry, while still having acceptable neutrino masses and enough suppression in flavor changing neutral currents. An approximate $U(2)$ flavor symmetry is an artifact of family-dependent gauge charges leading to a natural realization of the CKM mixing matrix. The model predicts sizeable violation of PMNS unitarity as well as a gauge vector leptoquark $U_1^\mu = ({\bf 3}, {\bf 1}, 2/3)$ which can be produced at the LHC -- both effects within the reach of future measurements. In addition, recently reported experimental anomalies in semi-leptonic $B$-meson decays, both in charged $b \to c \tau \nu$ and neutral $b \to s \mu \mu$ currents, can be accommodated.Comment: 9 pages, 5 tables. Version accepted for publication in PL

Ricci Reheating

We present a model for viable gravitational reheating involving a scalar field directly coupled to the Ricci curvature scalar. Crucial to the model is a period of kination after inflation, which causes the Ricci scalar to change sign thus inducing a tachyonic effective mass $m^{2} \propto -H^2$ for the scalar field. The resulting tachyonic growth of the scalar field provides the energy for reheating, allowing for temperatures high enough for thermal leptogenesis. Additionally, the required period of kination necessarily leads to a blue-tilted primordial gravitational wave spectrum with the potential to be detected by future experiments. We find that for reheating temperatures $T_{\rm RH} \lesssim 1$ GeV, the possibility exists for the Higgs field to play the role of the scalar field.Comment: 9 pages, 6 figure

Audible Axions

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 $f \gtrsim 10^{17}$ 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.Comment: 8 pages, 4 figures. References added, version submitted to JHE

Deconstructed Hypercharge: A Natural Model of Flavour

The flavour puzzle is one of the greatest mysteries in particle physics. A `flavour deconstruction' of the electroweak gauge symmetry, by promoting at least part of it to the product of a third family factor (under which the Higgs is charged) times a light family factor, allows one to address the flavour puzzle at a low scale due to accidentally realised $U(2)^5$ flavour symmetries. The unavoidable consequence is new heavy gauge bosons with direct couplings to the Higgs, threatening the stability of the electroweak scale. In this work, we propose a UV complete model of flavour based on deconstructing only hypercharge. We find that the model satisfies finite naturalness criteria, benefiting from the smallness of the hypercharge gauge coupling in controlling radiative Higgs mass corrections and passing phenomenological bounds. Our setup allows one to begin explaining flavour at the TeV scale, while dynamics solving the large hierarchy problem can lie at a higher scale up to around 10 TeV - without worsening the unavoidable little hierarchy problem. The low-energy phenomenology of the model is dominated by a single $Z'$ gauge boson with chiral and flavour non-universal couplings, with mass as light as a few TeV thanks to the $U(2)^5$ symmetry. The natural parameter space of the model will be probed by the HL-LHC and unavoidably leads to large positive shifts in the $W$-boson mass, as well as an enhancement in $\text{Br}(B_{s,d} \to \mu^+ \mu^-)$. Finally, we show that a future electroweak precision machine such as FCC-ee easily has the reach to fully exclude the model.Comment: 28 pages, 3 figures, 1 appendix. Version accepted for publication in JHE

Spatial extension of stochastic Pi calculus

We introduce a spatial extension of stochastic pi-calculus that provides a formalism to model systems of discrete, connected locations. We define the extended stochastic semantics and also give deterministic semantics in terms of a system of ordinary differential equations. We describe two simple examples, one based on a standard epidemic model and one modelling resistance in plant tissues