We investigate the Domain-Wall Standard Model (DWSM), a five-dimensional framework in which all Standard Model (SM) particles are localized on a domain wall embedded in a non-compact extra spatial dimension. A distinctive feature of this setup is the emergence of a Nambu–Goldstone (NG) boson, arising from the spontaneous breaking of translational invariance in the extra dimension due to the localization of SM chiral fermions. This NG boson couples via Yukawa interactions to SM fermions and their Kaluza–Klein (KK) excitations. We study the phenomenology of this NG boson and derive constraints from astrophysical processes (supernova cooling), Big Bang Nucleosynthesis (BBN), and collider searches for KK-mode fermions at the Large Hadron Collider (LHC). The strongest limits arise from LHC data: we reinterpret existing mass bounds on squarks and sleptons in simplified supersymmetric models (assuming a massless lightest neutralino), as well as limits on exotic hadrons containing long-lived squarks or long-lived charged sleptons in the regime of extremely small Yukawa couplings. From this analysis, we obtain a conservative lower bound of 1 TeV on the masses of KK-mode quarks and charged leptons. Finally, we discuss the prospects for producing KK-mode fermions at future high-energy lepton colliders and outline strategies to distinguish their signatures from those of sfermions.

United States

Puja Das

Nobuchika Okada

Digesh Raut

Desmond Villalba

Nambu–Goldstone boson phenomenology in domain-wall standard model

Smooth hybrid inflation is a hybrid inflation model that is free from topological defects and predicts the density perturbation with the spectral index of about 0.97. We show that the prediction on the spectral index is robust regardless the power of nonrenormalizable terms and meets with the latest results reported by Atacama Cosmology Telescope. Viable scenarios for baryogenesis and dark matter are also discussed.

Japan

Osamu Seto

Smooth hybrid inflation in light of ACT DR6 data

We investigate several phenomenological implications of the Weak Gravity Conjecture (WGC). We find that the WGC implies that the SM neutrinos must be electrically neutral, that the electric charge in the SM must be quantized, and that the photon must be massless. In addition, we use the WGC to set lower bounds on the electric charge of milli-charged particles (mCP), the gauge coupling of several <math altimg='si1.svg'><mi>U</mi><mo stretchy='false'>(</mo><mn>1</mn><mo stretchy='false'>)</mo></math> extensions of the SM, their kinetic mixing parameter with the SM <math altimg='si2.svg'><mi>U</mi><msub><mrow><mo stretchy='false'>(</mo><mn>1</mn><mo stretchy='false'>)</mo></mrow><mrow><mtext>EM</mtext></mrow></msub></math>, and the axion couplings to photons and fermions. We also set an upper bound on the lifetime of the proton.

India

Fayez Abu-Ajamieh

Sudhir K. Vempati

Implications of the weak gravity conjecture on charge, kinetic mixing, the photon mass, and more

We consider a classically conformal <inline-formula><tex-math id='TM0001' notation='LaTeX'>$U(1)$</tex-math></inline-formula> gauge extension of the Standard Model (SM), in which the <inline-formula><tex-math id='TM0002' notation='LaTeX'>$U(1)$</tex-math></inline-formula> gauge symmetry is radiatively broken by the Coleman&#8211;Weinberg mechanism. This breaking triggers the electroweak (EW) symmetry breaking through a mixed quartic coupling between the <inline-formula><tex-math id='TM0003' notation='LaTeX'>$U(1)$</tex-math></inline-formula> Higgs field and the SM Higgs doublet. For two Higgs boson mass eigenstates after the symmetry breaking, <inline-formula><tex-math id='TM0004' notation='LaTeX'>$h_1$</tex-math></inline-formula> (SM-like Higgs boson) and <inline-formula><tex-math id='TM0005' notation='LaTeX'>$h_2$</tex-math></inline-formula> (SM singlet-like Higgs boson), we calculate the Higgs boson trilinear coupling ( <inline-formula><tex-math id='TM0006' notation='LaTeX'>$g_{h_{1} h_{2} h_{2}}$</tex-math></inline-formula>) in the model by setting the Higgs boson mass spectrum to be <inline-formula><tex-math id='TM0007' notation='LaTeX'>$M_{h_1} &gt; 2 M_{h_2}$</tex-math></inline-formula>. For a common Higgs mass spectrum and mixing angle between two Higgs fields, we find that <inline-formula><tex-math id='TM0008' notation='LaTeX'>$g_{h_{1} h_{2} h_{2}}$</tex-math></inline-formula> in the classically conformal model is highly suppressed compared to that calculated for the conventional Higgs potential, where the <inline-formula><tex-math id='TM0009' notation='LaTeX'>$U(1)$</tex-math></inline-formula> and EW symmetry breaking originate from the negative squared masses for the Higgs fields at the tree-level. Thus, this coupling suppression is a striking nature of the radiative origin of EW symmetry breaking. We then consider how to distinguish this origin at the proposed International Linear Collider (ILC) via precise measurements of anomalous SM Higgs boson couplings and the search for anomalous SM Higgs boson decay <inline-formula><tex-math id='TM0010' notation='LaTeX'>$h_1 \rightarrow h_2 h_2$</tex-math></inline-formula> followed by <inline-formula><tex-math id='TM0011' notation='LaTeX'>$h_2 \rightarrow b \bar{b}$</tex-math></inline-formula>. We conclude that once the anomalous couplings are measured at the ILC, the observation of the anomalous Higgs boson decay is promising in the conventional Higgs potential, while this decay process is highly suppressed and undetectable for the classically conformal model.

Victor Baules

Experimentally Distinguishable Origin for Electroweak Symmetry Breaking

We propose a novel pathway to generate the electroweak scale (EW) via nonperturbative dynamics of a dark gauge sector based on the SU(N) gauge group. Imposing the scale invariance of the theory, we investigate the electroweak symmetry breaking (EWSB) which is triggered dynamically via the condensation of gauge fields. Instead of the usual dimension-4 triggered breaking, a dimension 6 term (with Wilson coefficient compatible with Standard Model Effective Field Theory (SMEFT) bounds) coupling the Higgs boson and the Yang-Mills field quadratic term in the Lagrangian provides feedback from the gauge to the Higgs sector. We provide a novel method to estimate a nonperturbative EW scale generation using the exact solution of a truncated set of the background equations of motion in Yang-Mills theory in terms of Jacobi elliptic functions and the exact beta-function valid in the strongly coupled regimes via the Dyson-Schwinger approach. Particularly, we find an analytical result for the renormalization group equation (RGE) of the gauge coupling in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi><mi>U</mi><mo stretchy="false">(</mo><mi>N</mi><mo stretchy="false">)</mo></math> sector in the strongly coupled regime. The dynamics studied in this paper pave the way to a more realistic model building with possible resolution to the hierarchy problem and, in general, dynamical generation of scales.

Italy

Marco Frasca

Poland

Anish Ghoshal

Nonperturbative origin of the electroweak scale: RGE in strongly-coupled dark gauge theories via the Dyson-Schwinger approach

We investigate the discovery potential at the MATHUSLA experiment of a long-lived particle (LLP), which is the heavier state of inelastic scalar dark matter (DM) in the third-generation-philic <inline-formula><tex-math id='TM0002' notation='LaTeX'>$U(1)$</tex-math></inline-formula> ( <inline-formula><tex-math id='TM0003' notation='LaTeX'>$U(1)_{X_3}$</tex-math></inline-formula>) extension of the Standard Model. Since the heavier state and DM state form a complex scalar charged under the <inline-formula><tex-math id='TM0004' notation='LaTeX'>$U(1)_{X_3}$</tex-math></inline-formula>, it is natural that the heavier state <italic>P</italic> is almost degenerate with the DM state and is hence long-lived. We find that the third-generation-philic right-handed <inline-formula><tex-math id='TM0006' notation='LaTeX'>$U(1)$</tex-math></inline-formula>, <inline-formula><tex-math id='TM0007' notation='LaTeX'>$U(1)_{R_3}$</tex-math></inline-formula>, model is the most interesting, because third-generation-philic models are less constrained by the current experimental results and right-handed <inline-formula><tex-math id='TM0008' notation='LaTeX'>$U(1)$</tex-math></inline-formula> interactions leave visible final decay products without produing neutrinos. For a benchmark of the model parameters consistent with the current phenomenological constraints, we find that the travel distance of the LLP can be <inline-formula><tex-math id='TM0009' notation='LaTeX'>$\mathcal {O}(100)$</tex-math></inline-formula>&#160;m and the LLP production cross section&#160;at the 14 TeV LHC can be <inline-formula><tex-math id='TM0010' notation='LaTeX'>$\mathcal {O}(10)$</tex-math></inline-formula> fb. Thus, we conclude that the LLP can be discovered at MATHUSLA with a sufficiently large number of LLP decay events inside the MATHUSLA detector.

Discovery Potential of a Long-Lived Partner of Inelastic Dark Matter at MATHUSLA in the <italic>U</italic>(1) <italic>X</italic>3 Extension of the Standard Model

We study the possibility of the highest energy neutrino event with 220 PeV energy, detected recently by the KM3NeT experiment to be originating from heavy dark matter (DM) decay. Considering a heavy right handed neutrino (RHN) DM for illustrative purposes, we show that DM mass of 440 PeV, can explain the observed flux. The required DM lifetime to produce the best-fit value of the neutrino flux saturates the existing gamma-ray bounds. Due to the large uncertainty in the flux, it is possible to explain the KM3NeT event from RHN DM decay at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>3</mn><mi>σ</mi></math> confidence level (CL) while being in agreement with gamma-ray bounds and nonobservation of similar events at IceCube. While we consider a gauged <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi><mo>−</mo><mi>L</mi></math> scenario where DM relic can be generated due to other interactions, we also briefly discuss some alternate DM possibilities where the gamma-ray bounds can be alleviated compared to the minimal RHN DM discussed here.

Debasish Borah

Nayan Das

China

Prantik Sarmah

Possible origin of the KM3-230213A neutrino event from dark matter decay

Why matter and dark matter contents of the Universe are of the same order of magnitude, is one of the puzzles of modern cosmology. At the face of it, this would seem to point toward a basic similarity between matter and dark matter, suggesting perhaps the widely discussed mirror world picture as an ideal setting for a discussion of this issue. Here we outline a new and simple mirror world scenario to explain this puzzle. Our model uses the Affleck-Dine mechanism to generate baryon asymmetry and dark matter relic density leading to an asymmetric dark matter picture. We find that, for a certain parameter range of the model, the mirror electron is the unique possibility for dark matter whereas, in the complementary parameter range, the mirror baryons constitute the dark matter. In either case, the mirror photon must have mass in the MeV range for consistency with observations. For the case of mirror electron dark matter, the model predicts a lower bound on the amount of dark radiation, i.e., <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Δ</mi><msub><mi>N</mi><mrow><mi>eff</mi></mrow></msub><mo>≥</mo><mn>0.007</mn></math>.

Rabindra N. Mohapatra

Matter-dark matter coincidence and the mirror world

We propose a generalized formulation of the Scalar Weak Gravity Conjecture (SWGC) based on the analogy with the derivation of the Gauge Weak Gravity Conjecture (GWGC). We discuss some phenomenological implications of this Generalized SWGC, including the scale of New Physics (NP) when applied to the SM Higgs sector, and the bounds on the axion's couplings to fermions and to the photon when it is applied to the axion. The Generalized SWGC constraints rule out most of the parameter space of axion-nucleon couplings, leaving only a tiny region.

The generalized scalar weak gravity conjecture and its implications

We use the weak gravity conjecture (WGC) to investigate the impact of charge dequantization arising from non-local QED on the scale of non-locality of neutrinos. We find this scale to be $$\lesssim 49$$ TeV as implied by direct bounds and $$\lesssim 15$$ TeV as implied by cosmological bounds, which could be probed in future colliders. We also investigate the electric force and potential in non-local QED and use them to reformulate the weak gravity conjecture (WGC) in non-local QED.