* I suspect that ultimately the speed of light is an average value, but at the ultimate quantum level, only an average value, and that deviations of the speed of light above or below the speed of light does not give rise to the phenomena associated with a tachyon in standard General Relativity, because the variation in the speed of light arises due to the space-time medium being slightly inhomogeneous at subatomic distance scales and hence to slight local variations in the true speed of light, rather than to true propagation of a particle in excess of the speed of light. I suspect this mostly due to the form of the path integral in the photon propagator in quantum electrodynamics which requires consideration of such paths and from the notion in loop quantum gravity that the dimensional and local nature of space-time is emergent, rather than a fundamental assumption of the theory.
* I suspect that space-time is ultimately local and real, but is not causal. In other words, I suspect that a real particle actually takes some particular path from point A to point B, but that sometimes events in the future influence events in the past, rather than visa versa. I suspect this mostly because quantum entanglement effects between two non-local effects always take place within the same light-cone connected at the point of entanglement. This suspicion also comes from the guess that deja vous is sometimes a result of genuine premonitions and not merely psychological hallucination.
* I suspect that H. Nikolic's construction of an energy-momentum tensor for the gravitational field in General Relativity (something that is commonly claimed not to exist), by using second as well as first derivatives to construct it, is correct, and is critically important to development of quantum gravity. This also means that total energy-momentum conservation does not need to be defined using a pseudo-tensor as a substitute.
* I suspect that dark matter phenomena are mostly a function of graviton self-interaction (as described in the previous post at this blog), of a cutoff in graviton wavelength that is a function of the size of the universe (something suggested by Lubos Motl in a post considering MOND theory), or of non-luminous ordinary matter emitted on the axis of the central black holes of galaxies and other kinds of non-luminous ordinary matter found in abundance only in galactic clusters (or some combination of the these sources), and that there is not, in fact, a non-Standard Model dark matter particle. But, this is not a strong expectation. If also believe that there is a reasonable probability that there would be a singlet massive dark matter fermion in the gravitational sector (perhaps a spin-1/2 sterile neutrino or a spin-3/2 gravitino), and that if there is one that it probably has a mass on the order of a 2 keV.
* I suspect that the Standard Model particle set, apart from a graviton (and possibly a singlet dark matter fermion, is complete) and that no new fundamental particles or forces (with the exceptions of a possible graviton and a light singlet dark matter fermion) will be discovered.
* I suspect that Mach's principle (i.e. the collective gravitational pull of all other mass-energy in the universe on each particle of mass-energy) explains inertia, rather than the Higgs field, which imparts mass to the Standard Model fermions, but is not the source of mass for the vast majority of the rest mass of the proton and the neutron which makes up the bulk of the rest mass in the universe that is not attributable to dark matter. Thus, inertia mass and gravitational mass are identical because inertia arises from gravity. Note that inertia, via the formula F=ma impacts the second derivative of position (i.e. acceleration), rather than the first derivative of position (i.e. velocity). So, that bosons with zero rest mass maintain a constant velocity (equal to c, the speed of light), does not contradict this formula so long as additional force impacts relativistic mass-energy, rather than speed.
* I suspect that neutrinos have Dirac mass arising from interactions with the weak force bosons (W+, W- and Z bosons) and the Higgs boson, rather than Majorana mass. I suspect this mostly because the non-identity of neutrinos and anti-neutrinos was the primary reason that they were hypothesized to exist in the first place, and because none of the Standard Model forces would interact with right handed neutrinos. Likewise, most right handed neutrino theories call for right handed neutrinos to have different masses than left handed neutrinos contrary to all other right handed version of Standard Model particles which have the same mass regardless of whether they are left handed, right handed, and regardless of their matter or anti-matter character.
* I suspect that the neutrino masses have a normal hierarchy, and that the mass of the electron neutrino is on the order of 1 meV or less.
* I suspect that there is a great deal of CP violation in the PMNS matrix.
* I suspect that no light sterile neutrinos of a mass necessary to explain the reactor anomaly exists, and that any difference between the measured value of the effective number of cosmological neutrinos, Neff and the theoretically predicted value with the three Standard Model neutrinos of 3.05 is due to experimental measurement error. A sufficiently heavy sterile reactor neutrino with a mass ca. 1 eV would not be inconsistent with cosmological measures of Neff, but would contradict cosmological measurements of the maximum sum of the combined neutrino mass states. The latest reactor measurements also tend to disfavor a four flavor oscillation model.
* I suspect that the anomaly in the radius of muonic hydrogen is due to experimental measurement error in the measurement of ordinary hydrogen, and conceptual theory errors in comparing the two. Similarly, I suspect that the anomalous magnetic moment of the muon relative to the theoretically predicted value in QED is due to an underestimate of systemic error in the relevant measurements.
* I suspect that two times the rest mass of the Higgs boson is exactly equal to twice the W boson rest mass plus the Z boson rest mass, subject only to a possible definitional adjustment for μ, the energy scale at which these masses are determined (this is a natural corollary to the fact that: "In the Standard Model, the Higgs field consists of four components, two neutral ones and two charged component fields. Both of the charged components and one of the neutral fields are Goldstone bosons, which act as the longitudinal third-polarization components of the massive W+, W–, and Z bosons. The quantum of the remaining neutral component corresponds to (and is theoretically realised as) the massive Higgs boson." The W and Z bosons are intimately related to the Higgs boson in the electroweak interaction, for example, with mass squared terms of these particles with the right signs and coefficients as the proposed simple relationship appearing in the kinetic term of the electroweak Lagrangian.
* I also suspect that the Higgs boson mass is a mass that implies a vacuum that is metastable, or a vacuum that is precisely on the bound between vacuum stability and vaccuum metability once quantum gravity effects are considered (see also here), and that it is a mass that maximizes photon decays. It also very nearly minimizes the second loop terms in the MS mass to pole mass conversion. It is not, however, a mass that causes the square of the masses of the Standard Model fermions to be exactly equal to the masses of the Standard Model bosons, although these are quite close to each other and might be equal as some energy scale given the running of the Standard Model particle masses.
* I suspect that the Higgs boson has exactly the properties predicted in the Standard Model for a Higgs boson mass of the magnitude measured, and that there are no additional Higgs bosons. This conclusion is strongly supported by experimental data to date.
* I suspect that the sum of the square of the rest masses of the fundamental particles is precisely equal to square of the Higgs vacuum expectation value, for a properly defined set of rest masses of these particles. Put another way, the sum of the Yukawa couplings to the Higgs field (or the equivalent in the case of the Higgs boson and weak force bosons) is unitary (i.e. exactly equal to 1.00).
* I suspect that all deviations between the Standard Model and actual physics at energy scales approaching the Planck scale are due to corrections for quantum gravity effects.
* I suspect that the discrepancy between the strength of the scalar dark energy field implied by the cosmological constant, and the strength of the Higgs vacuum expectation value, may arise because the Higgs vev is best understood as a short range field emitted by massive Standard Model fundamental particles that is absent in truly empty space, rather than as a scalar field that actually permeates the entire vacuum as a background field with which Standard Model fundamental particles interact.
* I suspect that a simultaneous solution for all six quarks of a generalization of Koide's rule that takes into account all of the quarks into which a quark can transform in an appropriate manner explains the relative masses of the six Standard Model quarks, and that Koide's rule is exact for the charged leptons subject only to deviations arising from the differences in the interactions of charged leptons with flavor oscillating neutrinos in W boson interactions with charged leptons. I also suspect that the relative neutrino masses fit a generalization of Koide's rule. I suspect that these Koide's rule relationships between the relative masses of the fundamental particles in the Standard Model arise dynamically from the weak force W boson interactions of quarks and leptons, with the Koide's ratio of 2/3rd representing a division of mass between a source particle, an intermediate particle, and its decay product, in the simple case, that is equidistant between a degenerate state of three equal masses and a maximally unequal state with two zero masses and one non-zero mass.
* I suspect that the difference between the masses of the neutrinos and the masses of the charged leptons is at some fundamental level tied to the relative strengths of the electromagnetic force which acts on all charged particles but not on the neutrinos, and the weak force, which acts on all massive Standard Model fundamental particles. The average ratio of charged lepton mass and neutrino mass might be equal to the ratio of the weak force coupling strength to the electromagnetic coupling strength, and a Koide's rule-like relationship might explain the relative masses of the three mass states. For example, the weak force is on the order of 1011 times weak than the electromagnetic force, while by comparison, the mass of the tau leptons is roughly 3.5*1010 times the mass of the heaviest neutrino mass eigenstate in a normal hierarchy with a lighest neutrino mass eigenstate of less than 1 meV. And, with those assumptions the mass of the muon is roughly 1.3*109 times the middle neutrino mass eigenstate. Perhaps, for example, only charged massive fermions interact directly with the Higgs field (as in the original Standard Model with massless neutrinos), and neutrinos acquire their masses indirectly, via W and Z boson interactions between charged leptons that acquire mass directly from the Higgs field, and neutrinos, that is roughly proportionate to the strength of these interactions. These interactions via the weak force might fulfill a role similar to hypothetical see-saw interactions between hypothetical right handed neutrinos and the Standard Model neutrinos. The slightly smaller ratio of interaction might flow from the fact that there are three separate weak fields (W+, Z and W-) interacting between the particles that add together to generate the neutrino masses. An alternative analysis arising from the same general observation considers the possibility that particle masses arise from self-interactions of particles with themselves.
* I suspect that QCD has no CP violation in the high energy perturbative QCD regime because gluons have zero rest mass and a massless force carrying boson does not experience time in general relativity (the same is true of photons and gravitons). But, since gluons appear to dynamically acquire mass in the low energy infrared regime when confined in hadrons, there might be CP violation in the low energy non-perturbative regime of QCD.
* I would not be surprised if the CP violation that the Standard Model explains as a CP violating phase of the CKM matrix (and probably the PMNS matrix as well) is actually an analytically distinct phenomena from the CKM matrix, and were related to each other. But, the small magnitude of CP violation effects in most CKM matrix elements relative to the magnitude of the non-CP violating effects, masks those effects in most contexts.
* I would not be surprised if the CKM matrix (apart from the CP violating phase) can be accurately parameterized with a single experimentally determined parameter, λ, with the value given to it in the Wolfenstein parameterization.
* I suspect that following the Big Bang at t=0+ε, that the universe was matter dominated and that this is balanced by an anti-matter universe on the other side of the Big Bang in which time seems to move in the opposite direction that is anti-matter dominated. Thus, I suspect that no baryon number violating or lepton number violating process sufficient to explain the baryon asymmetry of the universe will be discovered. In particular, this implies that neither proton decay, nor neutrinoless double beta decay, will ever be observed.
* I suspect that lepton flavor violation is as rare as it is predicted to be in the Standard Model in charged leptons (see also here and here), which arises only when induced by neutrino flavor oscillation. Note also that the GIM mechanism suppresses flavor changing neutral currents and charged lepton flavor violation in the Standard Model. A lack of charged lepton flavor violation largely follows from a conclusion that neutrinos have Dirac mass.
* I suspect that indications of violations of lepton universality will turn out to be statistical flukes or due to systemic errors.
* Juan Ramón González Álvarez argues that a field theory with a spin-2 graviton (presumably operating in the Minkowski space-time of special relativity) is not quite equivalent to the purely geometrical approach of classical General Relativity, but the differences between the two are quite subtle. These inconsistencies have long been a formidable barrier to unifying the Standard Model and General Relativity, in an analysis also driven in part by dissatisfaction with the energy-matter conservation pseudo-tensor of General Relativity. I wouldn't be at all surprised if reality actually involves a spin-2 graviton acting in a flat Minkowski space-time, rather than the curved space-time of General Relativity, in part because at the level of cosmology, space-time is remarkably flat.
* I suspect that there are only four space-time dimensions, although this may be an emergent property of space-time. Put another way, I suspect that models with Standard Model interactions limited to a four dimensional brane, while gravity operates in more dimensions, or a model with compactified extra dimensions (such as a Kaluza-Klein model), is not an accurate description of reality.
* I would not be surprised if the Standard Model force coupling constants converge due to slight tweaks in their beta functions at high energies that arise from subtle theoretical considerations or due to quantum gravity effects (e.g. asymptotic safety considerations). Weinberg had thought that there would be a unification of coupling constants in the Standard Model back in 1981, but subsequent data suggested otherwise.
For example, the QCD coupling constant beta function is, in part, a function of the effective number of quark flavors in the model. And, while usually, only five quark flavors of QCD hadronize, since the top quark has a lifetime about 1/10th of the typical hadronization time in QCD, theoretically, a small percentage of top quarks should live long enough to hadronize for a brief moment. This, in turn, might cause the number of effective hadronizing flavors in QCD in the real world to be 5.1 rather than 5, which might slightly impact the beta function of the QCD coupling constant αs at energies in excess of twice of the top quark mass (ca. 346 GeV). Current experimental measurements are not precise enough to distinguish a distinction between the beta function of 5 flavor QCD and 5.1 flavor QCD (the strong force coupling constant itself is known to a precision of roughly 0.6% in the weighted average although individual measurements vary by up to 3% or more from each other). Yet, a tweak of this magnitude could easily cause the strong force coupling constant to get 78% rather than 75% weaker between 1 TeV and a bit more than 1012 GeV as it would need to for there to be a gauge coupling constant unification at 1012 GeV where the electromagnetic coupling constant and weak force coupling constant converge in the Standard Model. A tweak of this nature, incidentally, would also make SUSY models, in which the three gauge coupling constants always do converge, less attractive because this feature would be replicated in the Standard Model.
Footnote: There is a nice power point summary of flavor physics in the Standard Model here.