The primary goal of the meeting is to discuss complementary aspects of elementary particle phenomenology both within the standard model and beyond: those relevant for the third and high luminosity runs of the Large Hadron Collider and possible future high energy colliders; in high intensity experiments measuring neutrino oscillations, quark/lepton number, flavour and CP violation; in astroparticle observatories probing the matter-energy content of the early and present universe. Planned topics to be covered include Higgs boson and electroweak physics, top quark physics, flavour phenomena and CP violation, neutrino physics, dark matter as well as other particle dynamics in the early universe. The program will consist of plenary talks covering recent theoretical advances in the field as well as a small number of experimental reviews.
I will report on the recent strategies for the determination of the genuine Standard Model predictions for several branching ratios for rare K and B decays. Subsequently constraints on Z' models following from these strategies will be discussed and a new mixing matrix for Z' interactions with quarks that is analogous to the CKM matrix will be presented.
Anomalies in the flavor sector have attracted significant attention in recent years. Of particular interest for this talk are those in the muon and electron magnetic dipole moments: the so-called g-2 anomalies. The present status of these could point towards the requirement for new physics that couples differently to leptons and muons. I will review the status of scalar leptoquark models as candidates for ameliorating these anomalies, focussing specifically on leptoquarks which have couplings to both left- and right-handed charged fermions as these can have an enhanced effect. We consider the case in which the electron and muon sectors are decoupled, and Yukawa couplings are specified using an up-type quark mass-diagonal basis. This allows us to identify a previously overlooked region of parameter space, where strong constraints from lepton flavor violating decays may be avoided. Whether or not these anomalies linger as the experimental landscape develops is an open question. Nonetheless, I will briefly outline why models capable of generating this type of signature are well-motivated for further study. This talk will be based on arXiv:2002.12544 and arXiv:2110.03707.
In this talk, recent advances in the theoretical description of axions and their interactions are presented. We start by recalling the principle of reparametrization invariance, based on the Goldstone boson nature of the axion. Using this principle as a tool, we discuss first the axion coupling to gauge bosons, and show that they are actually not driven by the anomalies. Then we describe the entanglement of the axion PQ symmetry with baryon and lepton numbers, and how this can be used phenomenologically for example to explain the neutron lifetime puzzle. Finally, we study how dark matter axions interact with SM fermions, and show that a direct EDM-like coupling for all charged fermions has been missed up to now. Being a prediction of the Dirac theory analogous to the g=2 magnetic moments, these EDMs would be rather large, possibly to the point of making the electron, neutron or atom EDMs our best probes for relic QCD axions over large swaths of parameter space.
While the axion was originally introduced to “wash out” CP violation from strong interactions, new sources of CP violation beyond QCD (needed to explain the matter-antimatter asymmetry) might manifest themselves via a tiny scalar axion-nucleon component. The latter can be experimentally probed in axion-mediated force experiments, as suggested long ago by J.E. Moody and F. Wilczek. In the present contribution, I will review CP-violating axion searches and highlight the special role of the QCD axion as a low-energy probe of high-energy sources of CP violation.
We study the impact of running effects on QCD axion phenomenology. Focusing on variants of DFSZ model, it is possible to suppress simultaneously both the axion couplings to nucleons and electrons, realising the so-called astrophobic axion scenarios, wherein the tight bounds from SN1987A and from stellar evolution of red giants and white dwarfs are greatly relaxed. This suppsression is not spoiled once renormalization group effects are included in the running of axion couplings. Given that astrophobic axion models generally feature flavour violating axion couplings, we also assess the impact of renormalization group effects on axion-mediated flavour violating observables.
I will discuss the possibility that the axion Peccei-Quinn symmetry is spontaneously broken after the beginning of inflation. This scenario interpolates between pre-inflationary and post-inflationary axion DM cosmology with significant phenomenological differences from both. In particular, large inflationary fluctuations are produced only at scales not constrained by CMB, avoiding the strongest isocurvature constraints. Nonetheless such large fluctuations lead to the formation of axion mini-clusters and are also constrained from Lyman-α forest and future CMB spectral distortion measurements. These aspects are common to a broad class of models where DM is produced by inflationary fluctuations: I will also comment on the generic features of such a scenario.
The 2021 measurement by the Fermilab experiment confirmed the 4 sigma discrepancy with the theory estimate based on the world average from the g-2 Theory Initiative. Since then, new lattice QCD results have been published and tend to reduce this tension.
In this talk, I will present some recent lattice calculations of the hadronic contributions to the muon g-2 and I will discuss their impact on the discrepancy with the experimental measurement.
We discuss the current status of the exclusive $b \to c \ell\nu$ decay modes and review the situation with hadronic uncertainties as well as with the problems related to a reliable extraction of $|V_{cb}|$. We also discuss the lepton flavor universality both in the decays of mesons and in the decays of baryons, and emphasize the importance of studying the angular distribution of these decay modes in order to test for the presence of BSM physics at low energies.
We present our predictions for lifetimes, lifetime ratios and
semileptonic decay widths of single-charm (bottom) and double-charm
baryons within the Heavy Quark Expansion (HQE) framework, including all
known corrections. In contrast to earlier findings, our results
accommodate the experimentally-favoured hierarchy of the singly charmed
baryons. In the double-charm sector, we find a good agreement with the
experimental value for the lifetime of $\Xi_{cc}^{++}$, and give predictions for the remaining two unmeasured lifetime ratios. Furthermore, we find an excellent agreement between the data and the experiment for the case of single-bottom baryons.
In this talk, I will revisit the Standard Model (SM) predictions for $\mathcal{B}(B \to K^{(\ast)}\nu\bar{\nu})$ and discuss the opportunities that open up when combining its partial decay with that of $\mathcal{B}(B → K^{(\ast)}\mu\mu)$. I will argue that the differential measurement of $B \to K\nu\bar{\nu}$ decays allow for an useful cross-check of the shape of the vector form-factor ($f_+(q^2)$), which is only computed at high-$q^2$ on the lattice and extrapolated to the physical region. I will then show that the ratios $\mathcal{B}(B \to K^{(\ast)}\mu{\mu})/\mathcal{B}(B \to K^{(\ast)}\nu\bar{\nu})$ allow for a clean extraction of $C_9^{\mu\mu}$, which is independent of the $B\to K^{(\ast)}$ form-factors to a first approximation. Lastly, I will show that the same ratio also proves to be more sensitive to the presence of New Physics in many plausible extensions of the SM.
Motivated by the direct discovery of gravitational waves (GWs) from black holes and neutron stars, there is a growing interest in investigating GWs from other sources. Among them, GWs from cosmic strings are particularly fascinating since they naturally appear in a large class of grand unified theories (GUTs). Remarkably, a series of pulsar-timing arrays (PTAs) might have already observed GWs in the nHz regime, hinting towards forming a cosmic string network in the early universe, which could originate from phase transition associated with the seesaw scale emerging from GUT. In this talk, I show that if these observations from PTAs are confirmed, GWs from cosmic strings, when combined with fermion masses, gauge coupling unification, and proton decay constraints, the parameter space of the minimal SO(10) GUT becomes exceedingly restrictive. The proposed minimal model is highly predictive and will be fully tested in a number of upcoming gravitational wave observatories.
We present the latest progress in analyzing the minimal potentially realistic non-supersymmetric $\mathrm{SO}(10)$ GUT model, whose scalar sector consists of representations $45+126+10$. Although the model is expected to give a robust proton decay prediction, any analysis is hampered by tachyonic instabilities present in the tree-level scalar potential. The one-loop corrected effective potential indicates that in the perturbative regime the only phenomenologically viable breaking pattern to the Standard Model is through an intermediate $\mathrm{SU}(4)\times\mathrm{SU}(2)\times\mathrm{U}(1)$ symmetry. Most recent developments, however, show that this region of parameter space does not admit a suitable fine-tuning associated to the EW-scale Higgs doublet, implying that the model is perturbatively not viable.
I will briefly discuss two ideas in dark matter model building. They first is that axion dark matter may be connected with neutrino mass generation, baryogenesis and flavour-dependent Higgs Yukawa couplings. The second arises within a continuing search for a good theory of the dark matter mass scale in the asymmetric dark matter paradigm. In particular, I will present some recent results on how a dark QCD sector may be relevant, building on an infrared fixed point idea proposed by Bai and Schwaller.
In this talk, we consider the phenomenology of electrically neutral complex vector particles V with a mass below the GeV-scale, but with higher dimensional form factor interactions to the SM photon. The astrophysics, cosmology and direct detection phenomenology will be presented.
The latest experimental results from CMS collaboration on Heavy Neutral Leptons will be presented. Various HNL production and decay modes are considered to guide the searches. The analysis of the full Run II data leads to stringent constraints on neutrino mass model parameters.
I discuss the interplay of terrestrial and cosmological neutrino mass determinations and highlight the exciting prospects for cosmological observations. Then I discuss a mechanism to modify neutrino evolution in the early Universe, to make "large" neutrino masses consistent with cosmology, and present a simple seesaw scenario to realise such a mechanism in a UV complete model.
Direct searches at fixed target experiments and searches for neutrinoless double beta (0νββ) decay can be used to probe the Majorana vs. pseudo-Dirac nature of a Heavy Neutral Lepton (HNL) pair. Firstly, I will outline a phenomenological parametrisation relating the active-sterile mixing strengths to the neutrino oscillation data, assuming that the HNL pair generates masses for two light neutrinos. I will then consider the possible constructive or destructive interference of the HNL pair with the light neutrino contribution in 0νββ decay and the production and decay of HNLs in fixed target experiments. Finally, I will explore how signals at LEGEND-1000 and DUNE constrain the HNL parameter space; in particular, the mass splitting between the HNL pair.
CP violation breaking is accidentally small in the SM: flavour invariants measuring CP violation in SMEFT are constructed and consequences on various flavour assumptions on their sizes are scrutinised.
The LHCb combined measurements of $\Delta a_{\rm CP} = a_{\rm CP} (D\to K^+K^-)- a_{\rm CP} (D\to \pi^+\pi^-)$ and $a_{\rm CP} (D\to K^+K^-)$ are in tension with predictions employing the Standard Model and U-spin symmetry of QCD. I discuss explanations in terms of new physics and propose test of these explanations in other $D$ decay modes.
Rare charm decays provide unique and complementary insights on flavor and BSM physics. We discuss status and progress in null test searches from theory on decays of charm mesons and baryons into invisibles, photons and leptons and where flavor experiments are currently pushing this frontier. We also discuss CP-violation together with sizable U-spin violation seen in hadronic 2-body decays.
In this talk I review vector-like quarks in leptons in flavour physics and EW precision observables in light of the W mass and the Cabibbo angle anomaly.
We emphasize the analogy between Vector-Like Quarks (VLQ) and Right Handed Neutrinos, illustrating how VLQ lead to naturally supressed FCNC and naturally small violations of 3x3 unitarity in the CKM matrix. VLQ provide a simple solution to the puzzle of eventual lack of unitarity in the first line of the CKM matrix and also provide a framework to have a realistic model with spontaneous CP violation with a complex CKM matrix, generated by real Yukawa couplings.
We strengthen the cosmological bound on the axion mass, by solving the momentum-dependent Boltzmann equations for axion-pion scatterings and by using a phenomenological production rate derived from pion-pion scattering data, overcoming the breakdown of chiral perturbation theory. Using present cosmological datasets we obtain m_a < 0.24 eV. To further improve the bound and exploit the reach of upcoming cosmological surveys, reliable non-perturbative calculations above the QCD crossover are needed.
We discuss examples of three Higgs doublet models which can provide good dark matter candidates. The emphasis is on models with S_3 symmetry, with or without spontaneous CP violation. Some aspects of the Weinberg potential will also be discussed.
I discuss the impact of triple-leptoquark interactions on matter stability for two specific proton decay topologies that arise at the tree- and one-loop level if and when they coexist. I furthermore demonstrate that the one-loop level topology is, in such an instance, much more relevant than the tree-level one despite the usual loop-suppression factor. To support that claim I present detailed analysis of the triple-leptoquark interaction effects on the proton stability within one representative scenario, where the scenario in question simultaneously features a tree-level topology that yields three-body proton decay $p \rightarrow e^+ e^+ e^-$ and a one-loop level topology that induces two-body proton decays $p \rightarrow \pi^0 e^+$ and $p \rightarrow \pi^+ \bar \nu $.
Rare b hadron decays are considered excellent probes of new semileptonic four-fermion interactions of microscopic origin. However, the same interactions also correct the high-mass Drell-Yan tails. In this work, we revisit the first statement in the context
of this complementarity and chart the space of short-distance new physics that could show up in rare b decays. We analyze the latest b → ql+l− measurements, where q = d or s and l = e or μ, including the most recent LHCb RK(∗) update, together with the latest charged and neutral current high-mass Drell-Yan data, pp → lν and pp → l+l−. We implement a sophisticated interpretation pipeline within the flavio framework, allowing us to investigate the multidimensional SMEFT parameter space thoroughly and efficiently. To showcase the new functionalities of flavio, we construct several explicit models featuring either a Z′ or a leptoquark, which can explain the tension in b → sμ+μ− angular distributions and branching fractions while predicting lepton flavor universality (LFU) ratios to be SM-like, as indicated by the recent data. Those models are then confronted against the global likelihood, including the high-mass Drell-Yan, either finding tensions or compatibility.
Light quark Yukawa couplings are notoriously difficult to measure: the HL-LHC will be able to constrain the first generation couplings only by a factor of few hundred times their SM value.
I will discuss Higgs pair production and the Higgs off-shell measurement as potential probes of light quark Yukawa couplings. For the Higgs pair production process I will discuss also how interpretable machine learning might be of use for constraining the up and down Yukawa couplings.
The Drell-Yan processes $pp\to\ell\nu$ and $pp\to\ell\ell$ at high transverse momentum can provide important probes of semileptonic transitions that are complementary to low-energy flavor physics observables. We parametrize possible New Physics (NP) contributions to these processes in terms of form-factors, and derive the corresponding bounds by recasting the latest ATLAS and CMS run 2 searches for mono- and di-lepton resonances. Moreover, we study the validity limit of the Standard Model Effective Field Theory (SMEFT) in this regime by comparing the limits obtained for specific tree-level mediators and their EFT equivalent. Both analyses are performed using HighPT, a new Mathematica package for automatic extraction of high-$p_T$ bounds.
Leptonic decays of neutral B mesons provide an excellent probe of physics beyond the Standard Model, due to the absence of tree-level flavour-changing neutral currents in the Standard Model and the corresponding smallness of the branching ratio. We present a Two-Higgs-Doublet model in which flavour-changing neutral Higgs couplings to up-type quarks can lift part of the SM suppression. The model contains three Yukawa spurions, allowing to systematically suppress FCNC couplings in the down-type quark sector. Within this model, the leading contributions to the scalar and pseudoscalar Wilson coefficients are calculated through next-to-leading order in QCD. Several experimental constraints from other $|\Delta B| = 1$ and $|\Delta B| = 2$ processes are discussed.
Measurements of the branching ratios of $B \to D^{(*)}\tau\bar\nu/B \to D^{(*)}\ell\bar\nu$ and $B_c\to J/\psi\, \tau\bar\nu/B_c\to J/\psi\, \ell\bar\nu$ by the BaBar, Belle and LHCb collaborations consistently point towards an abundance of taus compared to channels with light leptons. However, the ratio $\Lambda_b \to\Lambda_c \tau\bar\nu/\Lambda_b \to\Lambda_c \ell\bar\nu$ shows a relative deficit in taus. The aim of this talk is to critically address whether data still points towards a coherent pattern of deviations, in particular in light of the sum rule relating these decays in a model-independent way. We find that no common new physics explanation of all ratios is possible within $2\sigma$ or $1.5\sigma$, depending on the ${\cal R}(\Lambda_c)$ normalization to light lepton channels.
We derive a closed-form false vacuum decay rate at one loop for a single real scalar field in the thin wall limit. We obtain the bounce solution, together with the Euclidean action, counter-terms and RG running, and we extract the functional determinant via the Gel’fand-Yaglom theorem. Our procedure is valid for a generic spacetime dimension D, and we provide an explicit finite renormalized decay rate in D=3,4.
We present two lattice studies: The $\bar bb\bar qq$ systems with various quantum numbers using static bottom quarks and $\bar cc \bar qq$ systems with $I(J^{PC})=1(1^{+\pm})$.
Only one set of quantum numbers that couples to $Z_b$ and $\Upsilon\;\pi$ was explored on the lattice before; these studies found an attractive potential between $B$ and $\bar B^*$ resulting in a bound state below the threshold. The first study ($\bar bb\bar qq$) considers the other three sets of quantum numbers. Eigen-energies are extracted as a function of separation between $b$ and $\bar b$. The resulting eigen-energies do not show any sizable deviation from noninteracting energies of the systems $\bar bb+\bar qq$ and $\bar bq+\bar qb$, so no significant attraction or repulsion is found.
Our second study ($\bar cc \bar qq$) is the first study for four-quark states with $I(J^{PC})=1(1^{+\pm})$, a non-zero total momentum and two different lattice volumes. Our preliminary lattice results show that the energy shifts for eigenstates dominated by $D\bar{D}^*$ are very small in the $1^{++}$ channel and consistent with zero in the $1^{+-}$ channel. Our future plan is to determine the scattering amplitude for the coupled $J/\psi\pi - D\bar{D}^*$ scattering close to the $D\bar{D}^*$ threshold that reproduces experimental results and lattice spectra.
I'll review the current state of affairs in Cosmology. Data from Planck and from Stage III spectroscopic and photometric experiments have firmly established the flat $\Lambda$CDM as the standard cosmological model. Many parameters are now measured with the percent level precision. Nevertheless, some tensions remain, the strongest being the Hubble parameter tension between expansion rate of the Universe as constrained by cosmological probes and direct measurements. I will review the outcomes of community planning processes and describe the upcoming experiments such as CMB-S4 and MegaMapper. Finally, I will briefly discuss the new observation windows opened by gravitational waves, intensity mapping and lunar exploration.
The early Universe is usually assumed to be thermalised, homogeneous and isotropic, with only small fluctuations. However many new physics scenarios violate these assumptions: Phase transitions or displaced scalar fields lead to large deviations from thermal equilibrium, while topological defects like strings and domain walls represent large anisotropies. This talk will give an overview of these phenomena, and discuss their observable imprint in the form of gravitational waves and of CMB spectral distortions. Some recent progress in the study of phase transitions in strongly coupled theories will also be discussed.
I will show how first order phase transitions (PT) in the early universe, with relativistic bubble walls, constitute particle accelerators and colliders. These `bubbletrons' offer novel opportunities of observational access to very high energy scales, in addition to the gravitational waves from the PT. As two examples, I will discuss: i) non-adiabatic production of dark matter which is so fast to leave an imprint in the matter power spectrum, for dark matter masses of 10^8-10^9 GeV and a weak-scale PT; ii) production of relics beyond the GUT scale without the need for the universe to ever reach those temperatures.
A non-minimal dark sector could explain why WIMP dark matter has evaded detection so far. Based on the extensively studied example of a simplified t-channel dark matter model involving a colored mediator, we demonstrate that the Sommerfeld effect and bound state formation must be considered for an accurate prediction of the relic density and thus also when inferring the experimental constraints on the model. We find that parameter space thought to be excluded by LHC searches and direct detection experiments remains viable. Moreover, we point out that the search for bound state resonances at the LHC offers a unique opportunity to constrain a wide range of dark matter couplings inaccessible to prompt and long-lived particle searches.
We critically analyse the future of composite dynamics via the impact of non standard model Higgs on the (non) observed g-2 and W-mass anomalies.
The ultimate dream of unification models consists in combining both gauge and Yukawa couplings into one unified coupling. This is achieved by using a supersymmetric exceptional ${\rm E}_6$ gauge symmetry together with asymptotic unification in compact five-dimensional space-time. The ultraviolet fixed point requires exactly three fermion generations: one in the bulk, and the two light ones localised on the ${\rm SO}(10)$ boundary in order to cancel gauge anomalies. A second option allows to preserve baryon number and to lower the compactification scale down to the typical scales of the intermediate Pati-Salam gauge theory.
Subtle, but long-known, field-theoretical aspects require a more refined treatment of gauge theories involving a Brout-Englert-Higgs effect. This refinement can be analytically done using the Fröhlich-Morchio-Strocchi mechanism. In the standard model, this leads to slight, but in principle detectable, quantitative changes in observables. For many theories beyond the standard model, the effects are more drastic, and call in to question the viability of various models. Both aspects have significant implications for future colliders.
I will discuss how dark matter long range interactions with itself or with the baryons leave unique signatures in precision cosmological observables. I will present exquisitely sensitive probes of these interactions in galactic surveys and in 21cm cosmology and discuss the challenges of the theory predictions.
Nuclear reactions in the solar core can produce light and weakly coupled beyond the standard model particles that subsequently reach the Earth. We analyze the second step of the proton-proton chain, and we investigate the flux of monochromatic 5.49 MeV massive spin-one particles. Focusing on two benchmark scenarios, which correspond to different communication mechanisms with the visible sector, we evaluate the expected flux on the Earth. Finally, we explore the sensitivity reach of the next-generation large underground neutrino oscillation experiment Jiangmen Underground Neutrino Observatory (JUNO).
Sterile neutrinos are well-motivated extension of the Standard Model. In this talk I will focus on the interaction between sterile neutrinos and light active neutrinos through the magnetic moment portal. I will show that strong constraints can be derived from SN1987A through the non-observation of active neutrinos and photons produced from sterile neutrino decays. Furthermore, sensitivity projections for several present
and near-future experiments such as Fermi-LAT, e-ASTROGAM, DUNE and Hyper-Kamiokande will be shown for the future galactic supernova event.
The Tunneling Potential Formalism is an alternative to the Euclidean bounce for calculating tunneling actions, that control the decay of metastable vacua. In this talk I will discuss how this formalism can be extended to study other problems, from bubble-of-nothing decays to ungauged Q-balls and more.
The quantum tunneling in quantum field theory has attracted theoretical and phenomenological interests for a long time. Although it has been nearly established in the absence of gravity, there are subtleties in the presence of gravity. We re-formulated quantum tunneling with the Wheeler-deWitt equation and found that there is a possibility that a system may experience both Euclidean and Lorentzian evolution simultaneously. It allows us to consider a new class of tunneling processes having Euclidean evolution in one region and Lorentzian evolution in the others. We found that such a process can have a much higher tunneling rate than that of the well-known process with the Coleman-De Luccia bounce. We also found that the processes exist even in the decoupling limit of gravity and remain important at a low energy scale.
The limitations of symmetry-based solutions to naturalness problems have led to seeking answers from the early universe. In this talk I will give an overview of cosmological solutions to naturalness problems, focusing on models of cosmological relaxation and self-organised localisation.
We perform a comprehensive scan of the parameter space of a general singlet scalar
extension of the Standard Model to identify the regions which can lead to a strong first-
order phase transition, as required by the electroweak baryogenesis mechanism. We find
that taking into account bubble nucleation is a fundamental constraint on the parameter
space and present a conservative and fast estimate for it so as to enable efficient param-
eter space scanning. The allowed regions turn out to be already significantly probed by
constraints on the scalar mixing from Higgs signal strength measurements. We also con-
sider the addition of new neutrino singlet fields with Yukawa couplings to both scalars
and forming heavy (pseudo)-Dirac pairs, as in the linear or inverse Seesaw mechanisms
for neutrino mass generation. We find that their inclusion does not alter the allowed pa-
rameter space from early universe phenomenology in a significant way. Conversely, there
are allowed regions of the parameter space where the presence of the neutrino singlets
would remarkably modify the collider phenomenology, yielding interesting new signatures
in Higgs and singlet scalar decays.
The Large Hadron Collider (LHC) at CERN has enabled us to explore the frontiers of particle physics and understand the fundamental nature of the universe. In this talk, I will present a comprehensive overview of high pT physics analyses conducted in Run 2 of the LHC by both the ATLAS and CMS experiments. These analyses cover a broad range of topics, including measurements of the Higgs boson, searches for new physics beyond the Standard Model, and investigations into the properties of known particles.
In addition to presenting recent results, I will also provide a future outlook on High Energy Collider Physics, including the prospects for the High Luminosity LHC and future collider facilities.
We study the direct-detection rate for axial-vectorial dark matter scattering off nuclei in an SU(2) × U(1) invariant effective theory and compare it against the LHC reach. Current constraints from direct detection experiments are already bounding the mediator mass to be well into the TeV range for WIMP-like scenarios. This motivates a consistent and systematic exploration of the parameter space to map out possible regions where the rates could be suppressed. We do indeed find such regions and proceed to construct consistent UV models that generate the relevant effective theory. We then discuss the corresponding constraints from both collider and direct-detection experiments on the same parameter space. We find a benchmark scenario, where even for future XENONnT experiment, LHC constraints will have a greater sensitivity to the mediator mass.
Entropy production is a necessary ingredient for addressing the over-population of thermal relics. It is widely employed in particle physics models for explaining the origin of dark matter. A longlived particle that decays to the known particles, while dominating the universe, plays the role of the dilutor. We point out the impact of its partial decay to dark matter on the primordial matter power spectrum. For the first time, we derive a stringent limit on the branching ratio of the dilutor to dark matter from large scale structure observation using the SDSS data. This offers a novel tool for testing models with a dark matter dilution mechanism. We apply it to the left-right symmetric model and show that it firmly excludes a large portion of parameter space for right-handed neutrino warm dark matter.
TBA
We study the prospects of leptogenesis in the framework of the minimal flipped SU(5) gauge model in which the heavy Majorana neutrino mass scale is connected to the scale of unification via two-loop radiative effects. We argue that, in spite of a lower-than-usual seesaw scale, a successful thermal leptogenesis can take place in several regimes yielding a firm upper limit on the absolute light neutrino mass scale.