The regime of dark matter (DM) freeze-in at stronger coupling interpolates between freeze-in and freeze-out. It relies on Boltzmann-suppressed dark matter production, implying that the Standard Model bath temperature never exceeds the dark matter mass. In this work, we study this regime in the context of sterile neutrino dark matter, which can be sufficiently long-lived for a tiny sterile-active mixing. The sterile neutrino is assumed to couple to a real singlet scalar, providing for a thermal production mechanism of the former. We find that DM mass can range from GeV to tens of TeV consistently with all the constraints. The most interesting aspect of the consequent freeze-in phenomenology is that the sterile neutrino dark matter can be probed efficiently by both direct detection experiments and invisible Higgs decay at the LHC.

Estonia

Niko Koivunen

Finland

Oleg Lebedev

Martti Raidal

Probing sterile neutrino freeze-in at stronger coupling

The Belle II collaboration has recently observed the rare decay  $$B^+\rightarrow K^+ \nu \bar{\nu }$$  <math> <mrow> <msup> <mi>B</mi> <mo>+</mo> </msup> <mo>→</mo> <msup> <mi>K</mi> <mo>+</mo> </msup> <mi>ν</mi> <mover> <mrow> <mi>ν</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> </mrow> </math>  , finding an excess with respect to the Standard Model prediction. We explore the possibility that the data entails long-distance interactions induced by a massless dark photon,  $$\gamma _{\scriptscriptstyle {D}}$$  <math> <msub> <mi>γ</mi> <mstyle> <mi>D</mi> </mstyle> </msub> </math>  . This couples at the tree-level to an invisible, dark sector and to the Standard Model via higher-dimensional operators, such as the chromomagnetic-dipole coupling that we use to explain the excess. As the process  $$B^+\rightarrow K^+ \gamma _{\scriptscriptstyle {D}}$$  <math> <mrow> <msup> <mi>B</mi> <mo>+</mo> </msup> <mo>→</mo> <msup> <mi>K</mi> <mo>+</mo> </msup> <msub> <mi>γ</mi> <mstyle> <mi>D</mi> </mstyle> </msub> </mrow> </math>   is forbidden by angular momentum conservation, the transition mediated by the off-shell dark photon yields a three-body final state comprising a pair of dark fermions that show as a missing energy continuum in the detector, faking the neutrino signature. We show that the Belle II data is explained for perturbative values of the parameters of the model. This scenario predicts new contributions to the neutral B meson decays  $$B^0\rightarrow K^* \gamma _{\scriptscriptstyle {D}}$$  <math> <mrow> <msup> <mi>B</mi> <mn>0</mn> </msup> <mo>→</mo> <msup> <mi>K</mi> <mo>∗</mo> </msup> <msub> <mi>γ</mi> <mstyle> <mi>D</mi> </mstyle> </msub> </mrow> </math>  , in which the emission of a on-shell dark photon is allowed, yielding a monochromatic missing energy signature. Analogously, an excess due to the emission of a dark photon is predicted for the  $$B^0_s\rightarrow \phi + E_\textrm{miss}$$  <math> <mrow> <msubsup> <mi>B</mi> <mi>s</mi> <mn>0</mn> </msubsup> <mo>→</mo> <mi>ϕ</mi> <mo>+</mo> <msub> <mi>E</mi> <mtext>miss</mtext> </msub> </mrow> </math>   decay that could be scrutinized next at the LHCb experiments.

Italy

Emidio Gabrielli

Luca Marzola

Kristjan Müürsepp

Explaining the  $$B^+\rightarrow K^+ \nu \bar{\nu }$$  <math> <mrow> <msup> <mi>B</mi> <mo>+</mo> </msup> <mo>→</mo> <msup> <mi>K</mi> <mo>+</mo> </msup> <mi>ν</mi> <mover> <mrow> <mi>ν</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> </mrow> </math>   excess via a massless dark photon

The CMS experiment at CERN has reported a possible signal for a resonance at 146 GeV decaying into the eμ final state which, presently, is the only experimental hint for lepton flavour violation in any low- and high-energy experiment. The Froggatt-Nielsen mechanism naturally predicts the existence of new scalars, the flavons, with flavour off-diagonal couplings. We study this framework in the context of the CMS result and find that the minimal, purely leptophilic model is too restricted to match the claimed signal. Thereafter we show how models with additional flavon couplings to quarks can explain the claimed signal while satisfying all the existing constraints on lepton flavour violation.

Production and decays of 146 GeV flavons into eμ final state at the LHC

We study a non-supersymmetric SO(10) Grand Unification Theory with a very high energy intermediate symmetry breaking scale in which not only gauge but also Yukawa coupling unification are enforced via suitable threshold corrections and matching conditions. For gauge unification, we focus on a few symmetry breaking patterns with the intermediate gauge groups  $$\text {SU}(4)_{\textrm{C}} \times \text {SU}(2)_{\textrm{L}} \times \text {SU}(2)_{\textrm{R}}$$  <math> <mrow> <mtext>SU</mtext> <msub> <mrow> <mo>(</mo> <mn>4</mn> <mo>)</mo> </mrow> <mtext>C</mtext> </msub> <mo>×</mo> <mtext>SU</mtext> <msub> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> <mtext>L</mtext> </msub> <mo>×</mo> <mtext>SU</mtext> <msub> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> <mtext>R</mtext> </msub> </mrow> </math>   (Pati–Salam) and  $$\text {SU}(3)_{\textrm{C}} \times \text {SU}(2)_{\textrm{L}} \times \text {SU}(2)_{\textrm{R}}\times \text {U}(1)_{{\textrm{B}}-{\textrm{L}}}$$  <math> <mrow> <mtext>SU</mtext> <msub> <mrow> <mo>(</mo> <mn>3</mn> <mo>)</mo> </mrow> <mtext>C</mtext> </msub> <mo>×</mo> <mtext>SU</mtext> <msub> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> <mtext>L</mtext> </msub> <mo>×</mo> <mtext>SU</mtext> <msub> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> <mtext>R</mtext> </msub> <mo>×</mo> <mtext>U</mtext> <msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> <mrow> <mtext>B</mtext> <mo>-</mo> <mtext>L</mtext> </mrow> </msub> </mrow> </math>   (minimal left-right symmetry) assuming an additional global U(1) Peccei–Quinn symmetry, and having the Standard Model supplemented by a second Higgs doublet field at the electroweak scale. We derive the conditions as well as the approximate analytical solutions for the unification of the gauge coupling constants at the two-loop level and discuss the constraints from proton decay on the resulting high scale. Specializing to the case of the Pati–Salam intermediate breaking pattern, we then impose also the unification of the Yukawa couplings of third generation fermions at the high scale, again at the two-loop level. In the considered context, Yukawa unification implies a relation between the fermion couplings to the 10- and 126-dimensional scalar representations of the SO(10) group. We consider one such possible relation which is obtainable in an  $$\text {E}_6$$  <math> <msub> <mtext>E</mtext> <mn>6</mn> </msub> </math>   model where the previous two scalar fields are part of a single multiplet. Taking into account some phenomenological features such as the absence of flavor changing neutral currents at tree-level, we derive constraints on the parameters of the low energy model, in particular on the ratio of the two Higgs doublets vacuum expectation values  $$\tan \beta $$  <math> <mrow> <mo>tan</mo> <mi>β</mi> </mrow> </math>  .

Spain

Abdelhak Djouadi

Renato Fonseca

Ruiwen Ouyang

Non-supersymmetric SO(10) models with Gauge and Yukawa coupling unification

We consider the classically scale invariant Higgs-dilaton model of dynamical symmetry breaking extended with an extra scalar field that plays the role of dark matter. The Higgs boson is light near a critical boundary between different symmetry breaking phases, where quantum corrections beyond the usual Gildener-Weinberg approximation become relevant. This implies a tighter connection between dark matter and Higgs phenomenology. The model has only three free parameters, yet it allows for the observed relic abundance of dark matter while respecting all constraints. The direct detection cross section mediated by the Higgs boson is determined by the dark matter mass alone and is testable at future experiments.

Kristjan Kannike

Aleksei Kubarski

Alessandro Strumia

Venno Vipp

Dark matter-induced multi-phase dynamical symmetry breaking

The recently proposed multiphase criticality principle in Coleman-Weinberg models can provide a new explanation for the hierarchy between the electroweak and new physics scales. When applied to the Standard Model, a Higgs boson as light as the pseudo-Goldstone boson of broken-scale invariance occurs. The suppressed mixing between the two light fields still carries information about the large scale of symmetry breaking, albeit up to logarithmic corrections. In this work we probe this scenario with the present LHC data and assess the impact of future lepton and hadron colliders. Our results show that the multiphase criticality can easily explain the apparent absence of new physics at the energy scales tested in current experiments.

Katri Huitu

India

Subhadeep Mondal

Multiphase critical Higgs boson at colliders

We discuss the possibility of unifying in a simple and economical manner the Yukawa couplings of third generation fermions in a non-supersymmetric SO(10) model with an intermediate symmetry breaking, focusing on two possible patterns with intermediate Pati-Salam and minimal left-right groups. For this purpose, we assume a minimal Yukawa sector at high energy, starting with two Higgs bi-doublets at the intermediate scale which then simply reduce to a two Higgs doublet model at the electroweak scale. We first enforce gauge coupling unification at the two-loop level by including the threshold corrections in the renormalization group running which are generated by the heavy fields that appear at the intermediate symmetry breaking scale. We then study the running of the Yukawa couplings of the top quark, bottom quark and tau lepton at two-loops in these two breaking schemes, when the appropriate matching conditions are imposed. We find that the unification of the third family Yukawa couplings can be achieved while retaining a viable spectrum, provided that the ratio of the vacuum expectation values of the two Higgs doublet fields is large, <math><mi>tan</mi><mo>⁡</mo><mi>β</mi><mo>≈</mo><mn>60</mn></math>.

Yukawa coupling unification in non-supersymmetric SO(10) models with an intermediate scale

We show that the physical conditions which induce the Thakurta metric, recently studied by Bœhm et al. in the context of time-dependent black hole masses, correspond to a single accreting compact object in the entire Universe filled with isotropic non-interacting dust. In such a case, accretion physics is not local but tied to the properties of the whole Universe. We show that radiation, primordial black holes or particle dark matter cannot produce the specific energy flux required for supporting the mass growth of the compact objects described by the Thakurta metric. In particular, this solution does not apply to black hole binaries. We conclude that compact dark matter candidates and their mass growth cannot be described by the Thakurta metric, and thus existing constraints on the primordial black hole abundance from the LIGO-Virgo and the CMB measurements remain valid.

Gert Hütsi

Tomi Koivisto

Ville Vaskonen

Hardi Veermäe

Cosmological black holes are not described by the Thakurta metric: LIGO-Virgo bounds on PBHs remain unchanged

We introduce a new way of modeling the physics beyond the Standard Model by considering fake, strictly off-shell degrees of freedom: the fakeons. To demonstrate the approach and exemplify its reach, we re-analyze the phenomenology of the Inert Doublet Model under the assumption that the second doublet is a fakeon. Remarkably, the fake doublet avoids the most stringent Z-pole constraints regardless of the chosen mass scale, thereby allowing for the presence of new effects well below the electroweak scale. Furthermore, the absence of on-shell propagation prevents fakeons from inducing missing energy signatures in collider experiments. The distinguishing features of the model appear at the loop level, where fakeons modify the Higgs boson h → γγ decay width and the Higgs trilinear coupling. The running of Standard Model parameters proceeds as in the usual Inert Doublet Model case. Therefore, the fake doublet can also ensure the stability of the Standard Model vacuum. Our work shows that fakeons are a valid alternative to the usual tools of particle physics model building, with the potential to shape a new paradigm, where the significance of the existing experimental constraints towards new physics must necessarily be reconsidered.

Damiano Anselmi

Carlo Marzo

Aurora Melis

Marco Piva

Phenomenology of a fake Inert Doublet Model

The principle of multiple point criticality (PMPC), which allowed the prediction of the Higgs boson mass before its discovery, has so far been applied to radiatively generated vacua. If this principle is fundamental, following from some presently unknown underlying physics, the PMPC must apply to all vacua, including the multiple vacua of multi-scalar models dominated by tree-level terms. We first motivate this idea and then exemplify it by applying the PMPC to various realizations of singlet scalar dark matter models. We derive constraints on the dark matter properties from the requirement of degenerate vacua and show that some scalar dark matter models are ruled out by the PMPC, while in others the allowed parameters space is constrained.