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Lunar laser ranging accurately measures the distance between an observatory on Earth and a retroreflector on the Moon. Illustration not to scale.
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Existing capabilities in laser ranging, optical interferometry and metrology, in combination with precision frequency standards, atom-based quantum sensors, and drag-free technologies, are critical for the space-based tests of fundamental physics; as a result, of the recent progress in these disciplines, the entire area is poised for major advances...
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Space combined with a range of advanced technologies enables vitally important Fundamental Physics experiments that are impossible to perform on the ground. These in situ controlled experiments expand our understanding of nature in ways that are critically different from space based observational missions. In the following we describe recent work f...
The Satellite Test of the Equivalence Principle (STEP) will advance experimental limits on violations of Einstein's equivalence principle from their present sensitivity of two parts in 1013 to one part in 1018 through multiple comparison of the motions of four pairs of test masses of different compositions in a drag-free earth-orbiting satellite. W...
For the first time the AEgIS (Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy) experiment will measure the Earth's local gravitational acceleration g on antimatter through the evaluation of the vertical displacement of an antihydrogen horizontal beam. This will be a model independent test of the Weak Equivalence Principle at the base...
The AEgIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) experiment is designed with the objective to test the weak equivalence principle with antimatter by studying the free fall of antihydrogen in the Earth's gravitational field. A pulsed cold beam of antihydrogen will be produced by charge exchange between cold Ps excited in Rydb...
The GAUGE (GrAnd Unification and Gravity Explorer) mission proposes to use a drag-free spacecraft platform onto which a number of experiments are attached. They designed to address a number of key issues at the interface between gravity and unification with the forces of nature. The equivalence principle is to be probed with both a high-precision t...
Citations
... The dark photon in particular is a well-motivated candidate for dark matter and it has several possible production mechanisms, including a misalignment mechanism [22], arising naturally in certain string theories [23], tachyonic couplings to misaligned axions [24], and quantum flucuations during the inflationary epoch [25]. Constraints on the couplings of such particles to the Standard Model come from equivalence principle tests, such as of the Eöt-Wash group [26,27] and Lunar Laser Ranging groups [28,29]. Near future constraints will come from GW measurements, for example from black hole superradiance [30][31][32][33]. ...
The superradiant growth of massive vector fields in rotating black hole spacetimes has garnered significant attention in recent literature. However, the majority of these studies overlook the influence of a cosmological constant, which likely constitutes the primary energy content of our universe. In this paper, we extend recent research by incorporating a cosmological constant into the Einstein+Proca system and numerically evolving the resulting equations of motion. Utilizing the newly released GRBoondi numerical relativity code, designed specifically for the numerical evolution of (generalized) Proca fields, we discover that parameters causing a growing instability in the $\Lambda = 0$ scenario transition to a decaying state when $\Lambda > 0$. This results in a more intriguing phenomenology. These simulations pave the way for future full Einstein+Proca simulations to explore the secular decay of the resultant cloud from gravitational emission.
... Corresponding author of channels, including the misalignment mechanism in a non-minimal coupling to gravity [23], quantum fluctuations during inflation [24] and appearing naturally in the string theories [1]. Ones have carried out various kinds of experimental detection schemes to probe the ultralight particles, such as testing equivalence principle, where the constraints on the coupling effects of the ultralight particles to standard model are implemented by the Eöt-Wash group [25] and the Lunar Laser Ranging groups [26,27]. It may be advantageous that the GW detectors improve the limits on the ultralight fields. ...
The future space-borne gravitational wave detector, Laser Interferometer Space Antenna (LISA), has the potential of detecting the fundamental fields, such as the charge and mass ultra-light scalar field. In this paper we study the effect of lighter vector field on the gravitational waveforms from extreme mass-ratio inspirals (EMRI) system, consisting of a stellar-mass object and the massive black hole (MBH) in the Einstein-Proca theory of a massive vector field coupling to gravity. Using the perturbation theory, we compute the energy fluxes including the contributions of the Proca field and the gravitational field, then obtain the adiabatic inspiraling orbits and corresponding waveforms. Our results demonstrate that the vector charge and mass carried by the secondary body lead to detectable effects on EMRI waveform, and LISA has the potential to measure the mass of the Proca field with greater precision.
... Extensive experimental efforts have been devoted to searching for the effects of the fifth force across a wide range of distances and couplings [5]. One notable aspect of the fifth force searches is the exploration of the composition-dependent interactions [6], which could lead to violations of the weak equivalence principle (WEP) [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. The isospin-violating mediators, which have different couplings to neutrons and protons, are an intriguing type of compositiondependent interaction in fifth-force experiments and also of great interest in dark matter direct detection [23][24][25][26]. ...
... The parameter space of the isospin-violating mediators with mass ≲ 10 −11 eV is constrained by a number of experiments, including WEP, motions of asteroids [55,56] and planets [18,57], and black hole superradiance (BHSR) [58]. The dominant WEP experiments include the Eöt-Wash (EW) torsion balance experiment [9,10], the lunar laser ranging (LLR) experiments [19][20][21][22], and the MICROSCOPE experiment [11][12][13][14][15]. Note that the signals in the WEP experiments depend on the charges of both the test mass and the attractor (gravity source). ...
... While substituting different test masses can be relatively straightforward, changing attractors often presents more of a challenge due to the limited number of nearby celestial bodies. The most commonly used attractors include the Earth [9][10][11][12][13][14][15] and the Sun [10,[19][20][21][22]. Another critical factor in the fifth force experiments is the distance. ...
A bstract
Gravitational wave (GW) signals arising from binary neutron star mergers offer new, sensitive probes to ultralight mediators. Here we analyze the GW signals in the GW170817 event detected by the LIGO/Virgo collaboration to impose constraints on the ultralight isospin-violating mediator that has different couplings to protons and neutrons. Neutron stars, which primarily consist of neutrons, are the ideal places to probe the isospin-violating mediator. Such a mediator can significantly alter the dynamics of the binary neutron star mergers, through both the long-range Yukawa force and the new dipole radiation. We compute the gravitational waveform by taking into account the new physics effects due to the isospin-violating mediator and use the Bayesian inference to analyze the gravitational wave data in the GW170817 event. We find that although the current fifth force experiments (including MICROSCOPE and EW) often provide more stringent constraints than the GW170817 data, in the parameter space where the isospin-violating force is completely screened by the Earth (namely, the Earth is charge neutral under this force), the GW170817 data offer the leading constraints: the upper bound on the neutron coupling is f n ≲ 10 ⁻¹⁹ in the mediator mass range of ≃ (3 × 10 ⁻¹⁶ , 5 × 10 ⁻¹⁴ ) eV.
... Other production mechanisms include tachyonic couplings to a misaligned axion [45] and quantum fluctuations during inflation [46]. Constraints on the couplings of such particles to the standard model come from equivalence principle tests, such as of the Eöt-Wash group [47,48] and Lunar Laser Ranging groups [49][50][51]. Near future constraints will come from GW measurements, for example from black hole superradiance [52][53][54][55]. Current constraints in the literature coming from superradiance suggest LISA would be able to constrain the mass of the vector field in the range 1×10 −16 eV to 6×10 −16 eV [56]. ...
The advent of gravitational wave astronomy has seen a huge influx of new predictions for potential discoveries of beyond the Standard Model fields. The coupling of all fundamental fields to gravity, together with its dominance on large scales, makes gravitational physics a rich laboratory to study fundamental physics. This holds especially true for the search for the elusive dark photon, a promising dark matter candidate. The dark photon is predicted to generate instabilities in a rotating black hole spacetime, birthing a macroscopic Bose-Einstein condensate. These condensates can especially form around super massive black holes, modifying the dynamical inspiralling process. This then opens another window to leverage future space-borne gravitational wave antennas to join the hunt for the elusive dark matter particle. This study builds a preliminary model for the gravitational waveform emitted by such a dressed extreme mass-ratio inspiral. Comparing these waveforms to the vacuum scenario allows projections to the potential constrainability on the dark photon mass by space-borne gravitational wave antennas. The superradiant instability of a massive vector field on a Kerr background is calculated and the modification to the dynamics of an inspiralling solar mass-scale compact object is determined with approximations on the backreaction effect of the cloud on the compact object. The end result is the projection that the LISA mission should be able to constrain the dark photon mass using extreme mass ratio inspirals in the range $[1.8 \times 10^{-17}, 4.47 \times 10^{-16}]$ eV.
... But regardless of its empirical success, it demonstrates that the predictions made by LNR theories are not necessarily being calculated correctly in present studies. The notable example is the LLR study of changing G [Turyshev, 2007]. The analysts assume GTR to be the correct background theory, and carefully make calculations and models for the GTR-based theory. ...
... Instead, perhaps it has gained a new momentum after the discovery of accelerating universe. The present cosmological picture emerging out of SN Ia observations [40,41] reveals that the present universe is accelerating. Some kind of exotic repulsive force in the form of vacuum energy is supposed to be responsible for this acceleration which started about 7 Gyr ago. ...
... Suppose that two dimensionless numbers are randomly chosen first (e.g. and D), and they turn out to be 10 3 and 10 40 . This gives a range of expectations for further numbers we "randomly" select. ...
In his [1937, 1938], Paul Dirac proposed his “Large Number Hypothesis” (LNH), as a speculative law, based upon what we will call the “Large Number Coincidences” (LNC’s), which are essentially “coincidences” in the ratios of about six large dimensionless numbers in physics. Dirac’s LNH postulates that these numerical coincidences reflect a deeper set of law-like relations, pointing to a revolutionary theory of cosmology. This led to substantial work, including the development of Dirac’s later [1969/74] cosmology, and other alternative cosmologies, such as Brans-Dicke modifications of GTR, and to extensive empirical tests. We may refer to the generic hypothesis of “Large Number Relations” (LNR’s), as the proposal that there are lawlike relations of some kind between the dimensionless numbers, not necessarily those proposed in Dirac’s early LNH.
Such relations would have a profound effect on our concepts of physics, but they remain shrouded in mystery. Although Dirac’s specific proposals for LNR theories have been largely rejected, the subject retains interest, especially among cosmologists seeking to test possible variations in fundamental constants, and to explain dark energy or the cosmological constant. In the first two sections here we briefly summarise the basic concepts of LNR’s. We then introduce an alternative LNR theory, using a systematic formalism to express variable transformations between conventional measurement variables and the true variables of the theory. We demonstrate some consistency results and review the evidence for changes in the gravitational constant G.
The theory adopted in the strongest tests of Ġ/G, by the Lunar Laser Ranging (LLR) experiments, assumes: Ġ/G = 3(dr/dt)/r – 2(dP/dt)/P – (dm/dt)/m, as a fundamental relationship. Experimental measurements show the RHS to be close to zero, so it is inferred that significant changes in G are ruled out. However when the relation is derived in our alternative theory it gives: Ġ/G = 3(dr/dt)/r – 2(dP/dt)/P – (dm/dt)/m – (dR/dt)/R. The extra final term (which is the Hubble constant) is not taken into account in conventional derivations. This means the LLR experiments are consistent with our LNR theory (and others), and they do not really test for a changing value of G at all. This failure to transform predictions of LNR theories correctly is a serious conceptual flaw in current experiment and theory.
... If m φ H(v), ignoring the initial misalignment still gives parametrically the correct result, since it can give at most an O(1) correction on top of the EW-induced misalignment. Therefore modulo O(1) factors, we get [62][63][64][65][66][67][68][69][70] and stellar cooling constraints [71]. The red solid line shows the target given by φ − reproducing the observed dark matter relic density. ...
... In figure 8 we show this ultralight DM target and current constraints on our parameter space. The bounds include tests of the equivalence principle [59][60][61], tests of the Newtonian and Casimir potentials (5th force) [62][63][64][65][66][67][68][69][70] and stellar cooling [71]. Future probes of φ − dark matter, including torsion balance experiments [75], atom interferometry [76], optical/optical clock comparisons and nuclear/optical clock comparisons [77], resonant mass detectors (DUAL and SiDUAL [78]) and gravitational-wave detectors [79,80] are orders of magnitude too weak to probe our parameter space. ...
A bstract
We present a cosmological solution to the electroweak hierarchy problem. After discussing general features of cosmological approaches to naturalness, we extend the Standard Model with two light scalars very weakly coupled to the Higgs and present the mechanism, which we recently introduced in a companion paper to explain jointly the electroweak hierarchy and the strong-CP problem. In this work we show that this solution can be decoupled from the strong-CP problem and discuss its possible implementations and phenomenology. The mechanism works with any standard inflationary sector, it does not require weak-scale inflation or a large number of e-folds, and does not introduce ambiguities related to eternal inflation. The cutoff of the theory can be as large as the Planck scale, both for the Cosmological Constant and for the Higgs sector. Reproducing the observed dark matter relic density fixes the couplings of the two new scalars to the Standard Model, offering a target to future axion or fifth force searches. Depending on the specific interaction of the scalars with the Standard Model, the mechanism either yields rich phenomenology at colliders or provides a novel joint solution to the strong-CP problem. We highlight what predictions are common to most realizations of cosmological selection of the weak scale and will allow to test this general framework in the near future.
... In Fig. 9 we also show laboratory and astrophysical constraints on ϕ DM. They include tests of the equivalence principle [142][143][144][145], tests of the Newtonian and Casimir potentials (5th force) [146][147][148][149][150][151][152][153][154], stellar cooling [155], and black hole super-radiance [156,157]. Fifth force and equivalence principle constraints were translated on bounds on the trilinear coupling of a scalar coupled to the Higgs boson in [160,161]. ...
... FIG. 9. Laboratory and astrophysical constraints on scalars coupled to the Higgs boson via the trilinear interaction κm ϕ P n ϕ i¼1 ϕ i jHj 2 = ffiffiffiffiffi n ϕ p [we neglect unimportant Oð1Þ factors introduced by the mixing of the two Higgses]. The bounds include tests of the equivalence principle [142][143][144][145], tests of the Newtonian and Casimir potentials (5th force) [146][147][148][149][150][151][152][153][154], stellar cooling [155], and black hole super-radiance [156,157]. The pink solid line shows the target given by the scalars being dark matter. ...
Does the value of the Higgs mass parameter affect the expectation value of local operators in the Standard Model? For essentially all local operators the answer to this question is “no”, and this is one of the avatars of the hierarchy problem: Nothing is “triggered” when the Higgs mass parameter crosses zero. In this article, we explore settings in which Higgs mass parameters can act as a “trigger” for some local operators OT. In the Standard Model, this happens for OT=Tr(GG˜). We also introduce a “type-0” two Higgs doublet model, with a Z4 symmetry, for which OT=H1H2 is triggered by the Higgs masses, demanding the existence of new Higgs states necessarily comparable to or lighter than the weak scale, with no wiggle room to decouple them whatsoever. Surprisingly, this model is not yet entirely excluded by collider searches, and will be incisively probed by the high-luminosity run of the LHC, as well as future Higgs factories. We also discuss a possibility for using this trigger to explain the origin of the weak scale, invoking a landscape of extremely light, weakly interacting scalars ϕi, with a coupling to OT needed to make it possible to find vacua with small enough cosmological constant. The weak scale trigger links the tuning of the Higgs mass to that of the cosmological constant, while coherent oscillations of the ϕi can constitute dark matter.
... Below 0.1 eV, laboratory tests of gravity and gravity-like forces provide highly restrictive constraints, including high precision tests of the inverse-square law (gravity ∝ r −2 ) [57,58] and of the equivalence principle via torsion-balance experiments [59] and lunar laser-ranging (LLR) measurements [59,60]. Besides, measurements of the Casimir effect [61] could set a limit that is slightly stronger than that from the inverse-square law when 0.05 m Z /eV 0.1, which is not presented in figure 2. Also not presented here is the bound from black hole superradiance [62], which would only enter the lower left corner in figure 2. We refer to our previous work [24] for more detailed discussions on the long-range force searches and present only the dominant constraints from torsion-balance tests of the inverse-square law and the equivalence principle. ...
A bstract
We consider a generic dark photon that arises from a hidden U(1) gauge symmetry imposed on right-handed neutrinos ( ν R ). Such a ν R -philic dark photon is naturally dark due to the absence of tree-level couplings to normal matter. However, loop-induced couplings to charged leptons and quarks are inevitable, provided that ν R mix with left-handed neutrinos via Dirac mass terms. We investigate the loop-induced couplings and find that the ν R -philic dark photon is not inaccessibly dark, which could be of potential importance to future dark photon searches at SHiP, FASER, Belle-II, LHC 14 TeV, etc.
... Despite the small value of the loop-induced coupling, the magnitude coincides with the sensitivity of current precision tests of gravity. For long-range forces mediated by ultralight bosons coupled to electrons or quarks, experimental tests of the strong (based on the lunar laser-ranging technology [9]) and weak (e.g., torsion-balance experiments [10,11]) equivalence principles are sensitive to Yukawa/gauge couplings spanning from 10 −20 to 10 −24 . Very recently, gravitational waves from black hole (BH) and neutron star (NS) binary mergers have been detected by the LIGO/VIRGO collaboration [12,13], providing novel methods to test theories of gravity as well as other long-range forces [14][15][16][17][18][19][20][21][22][23][24]. ...
... (4.3), the value of y φ depends on neutrino masses and the Yukawa couplings of φ to ν R . Since there are many free parameters in Y R and M ν (where Majorana phases, the Dirac CP phase, the lightest neutrino mass are still unknown), we would like to simply parametrize y φ as follows: [56], tests of gravitational inverse-square law (orange) [57], lunar laser-ranging (LLR, green) measurements [9,56], and black hole superradiance (hatched bands) [15]. ...
... In addition, precision measurements of binary pulsar systems are also sensitive to the muonic force (orange curves) [24]. pulses is also sensitive to new long-range forces [9]. These two bounds, reviewed in ref. [56], are presented in figure 3 and overlap with the theoretically most favored region (red lines). ...
A bstract
Right-handed neutrinos ( ν R ) are often considered as a portal to new hidden physics. It is tempting to consider a gauge singlet scalar ( ϕ ) that exclusively couples to ν R via a ν R ν Rϕ term. Such a ν R -philic scalar does not interact with charged fermions at tree level but loop-induced effective interactions are inevitable, which are systematically investigated in this work. The magnitude of the loop-induced couplings coincidentally meets the current sensitivity of fifth-force searches. In particular, the loop-induced coupling to muons could be tested in the recent LIGO observations of neutron star mergers as there might be a sizable Yukawa force in the binary system mediated by the ν R -philic scalar.
... Despite the small value of the loop-induced coupling, the magnitude coincides with the sensitivity of current precision tests of gravity. For long-range forces mediated by ultra-light bosons coupled to electrons or quarks, experimental tests of the strong (based on the lunar laser-ranging technology [8]) and weak equivalence principles (e.g., torsion-balance experiments [9,10]) are sensitive to Yukawa/gauge couplings spanning from 10 −20 to 10 −24 . Very recently, gravitational waves from black hole (BH) and neutron star (NS) binary mergers have been detected by the LIGO/VIRGO collaboration [11,12], providing novel methods to test theories of gravity as well as other long-range forces [13][14][15][16][17][18][19][20][21][22][23]. ...
... So far, the Eöt-Wash torsion-balance experiment has performed WEP tests with the highest precision [9,10], leading to the most stringent constraint on y φee in the regime of very small m φ . In addition, the lunar laser-ranging (LLR) technology which is able to measure the varying distance between the moon and the earth to high precision using laser pulses is also sensitive to new long-range forces [8]. These two bounds, reviewed in Ref. [52], are presented in Fig. 4 and overlap with the theoretically most favored region (red lines). ...
... But all these bounds are significantly higher than the largest expected values of y φee -see Ref. [34] for a recent compilation of these bounds. [52], tests of gravitational inverse-square law (orange) [53], lunar laser-ranging (LLR, green) measurements [8,52], and black hole superradiance (hatched bands) [14]. ...
Right-handed neutrinos ($\nu_{R}$) are often considered as a portal to new hidden physics. It is tempting to consider a gauge singlet scalar $(\phi)$ that exclusively couples to $\nu_{R}$ via a $\nu_{R}\nu_{R}\phi$ term. Such a $\nu_{R}$-philic scalar does not interact with charged fermions at tree level but loop-induced effective interactions are inevitable, which are systematically investigated in this work. The magnitude of the loop-induced couplings coincidentally meets the current sensitivity of fifth-force searches. In particular, the loop-induced coupling to muons could be tested in the recent LIGO observations of neutron star mergers as there might be a sizable Yukawa force in the binary system mediated by the $\nu_{R}$-philic scalar.
